Teach-In Electronics

1. 50 Everyday Practical Electronics, November 2010 Teach-In 2011 By Mike and Richard Tooley 0ARTªª)NTRODUCTIONªTOªSIGNALSªINª ELECTRONICªCIRCUITSªANDªSYSTEMS /URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEªª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS

2. ªASªWELLªASªELECTRONICSªUNITSª OFªTHEªNEWª$IPLOMAªINª%NGINEERINGª ALSOªATª,EVELª ª4HEªSERIESªWILLªALSOªPROVIDEªTHEªMOREªEXPERIENCEDªREADERª WITHªANªOPPORTUNITYªTOª@BRUSHªUP ªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª %ACHªPARTªOFªOURª4EACH )NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARN

3. ª#HECK

4. ªUILD

5. ª)NVESTIGATEªANDª !MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORY

6. ª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDING

7. ªANDªUILDªWILLªGIVEª YOUªANªOPPORTUNITYªTOªBUILDªANDªTESTªSIMPLEªELECTRONICªCIRCUITSª)NVESTIGATEªWILLªPROVIDEªYOUªWITHªAªCHALLENGEª WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNING

8. ªANDªlNALLY

9. ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ª TO RECOGNISE SIGNALS FROM THE SHAPE OF THEIR WAVEFORMS EING ABLE TO lREADm AND INTERPRET A CIRCUIT DIAGRAM OR lSCHEMATICm IS AN ESSENTIAL SKILL REQUIRED OF EVERY ELEC TRONIC TECHNICIAN AND ENGINEER -ANY DIFFERENT PARTS AND DEVICES ARE USED IN ELECTRONIC CIRCUITS

10. AND IT IS IMPORTANT THAT YOU SHOULD BE ABLE TO RECOGNISE THEM

11. BOTH FROM THE SYMBOLS THAT WE USE TO REPRESENT THEM IN THEORETICAL CIRCUIT DIAGRAMS AND ALSO FROM THEIR PHYSICAL APPEARANCE ERS FORMS OF lBODY LANGUAGEm )N FACT

12. LIFE WOULD BE VERY DIFÚCULT WITHOUT SIGNALS q THINK ABOUT DRIVING A CAR OR MOTORBIKE IN HEAVY TRAFÚCØ )N THIS SECTION WE WILL LOOK AT HOW SIGNALS ARE USED IN ELECTRONICS

13. HOW THEY CAN BE CONVERTED FROM ONE FORM TO ANOTHER

14. AND HOW THEY ARE MEASURED )N ELECTRONICS

15. SIGNALS CAN TAKE MANY FORMS INCLUDING CHANGES IN VOLTAGE LEVELS

16. PULSES OF CURRENT

17. AND SEQUENCES OF BINARY CODED DIGITS OR CJUT 3IGNALS THAT VARY CONTINUOUSLY IN LEVEL ARE REFERRED TO AS ANALOGUE SIG NALS

18. WHILE THOSE THAT USE DISCRETE IE ÚXED LEVELS ARE REFERRED TO AS DIGITAL SIGNALS 3OME TYPICAL ANALOGUE AND DIGITAL SIGNALS ARE SHOWN IN IG .OTICE HOW THE DIGITAL SIGNAL EXISTS ONLY AS A SERIES OF DISCRETE VOLTAGE LEVELS

19. WHILE THE ANALOGUE SIGNAL VARIES CONTINUOUSLY FROM ONE VOLTAGE LEVEL TO ANOTHER 7($+,1 $ %52$'%$6(' ,1752'87,21 72 (/(7521,6 : % %'). THIS NEW 5FBDI*O SERIES BY INTRODUCING THE SIGNALS USED TO CONVEY INFORMATION IN ELECTRONIC CIRCUITS

20. AND THE UNITS THAT WE USE TO MEASURE THE QUANTITIES IN ELECTRONIC CIRCUITS 7E CONCLUDE THIS PART BY LOOKING AT SOME SIMPLE ELECTRONIC CIRCUITS THAT YOU CAN BUILD AND TEST USING #IRCUIT 7IZARD SOFTWARE SEE PAGES AND 3IGNALSªINªELECTRONICªCIRCUITSª ANDªSYSTEMS 4HIS ÚRST PART OF OUR 4EACH )N SERIES WILL PROVIDE YOU WITH AN INTRODUC TION TO THE SIGNALS THAT CONVEY JO GPSNBUJPO IN ELECTRONIC CIRCUITS 7E WILL ALSO INTRODUCE YOU TO SOME OF THE UNITS THAT ARE USED WHEN MEASURING ELECTRICAL QUANTITIES

21. SUCH AS CUR RENT

22. VOLTAGE AND FREQUENCY 9OU WILL LEARN ABOUT THE DIFFERENCE BETWEEN ANALOGUE AND DIGITAL SIGNALS AND HOW ,EARN 3IGNALSªANDªSIGNALªCONVERSION )N ALL FORMS OF COMMUNICATION SIG NALS ARE USED TO CONVEY INFORMATION 4HE SIGNALS THAT WE USE IN EVERYDAY LIFE CAN TAKE MANY FORMS

23. INCLUDING ÛASHING LIGHTS

24. SHOUTING

25. WAVING OUR HANDS

26. SHAKING OUR HEADS AND OTH

27. Everyday Practical Electronics, November 2010 51 Teach-In 2011 3IGNALS CAN ALSO BE QUITE EASILY CONVERTED FROM ONE FORM TO ANOTHER OR EXAMPLE

28. THE SIGNAL FROM THE STAGE MICROPHONE AT A LIVE RADIO BROADCAST WILL BE AN ANALOGUE SIGNAL AT THE POINT AT WHICH THE ORIGINAL SOUND IS PRODUCED IE ON STAGE !FTER APPROPRIATE PROCESSING WHICH MIGHT INVOLVE AMPLIÚCATION ANDOR REMOVAL OF NOISE AND OTHER UNWANTED SOUNDS IT MIGHT THEN BE CONVERTED TO A DIGITAL SIGNAL FOR RADIO TRANSMIS SION

29. AND THEN CONVERTED BACK TO AN ANALOGUE SIGNAL BEFORE BEING AMPLI ÚED AND SENT TO THE LOUDSPEAKER AT THE POINT OF RECEPTION ! DEVICE THAT CONVERTS AN ANALOGUE SIGNAL TO DIGITAL FORMAT IS CALLED AN BOBMPHVFUPEJHJUBM DPOWFSUFS !$#

30. WHILE ONE THAT CONVERTS A DIGITAL SIGNAL TO ANALOGUE IS REFERRED TO AS A EJHJUBMUPBOBMPHVF DPOWFSUFS $!# !N ELECTRONIC SYSTEM THAT USES BOTH ANALOGUE AND DIGITAL SIGNALS IS SHOWN IN IG %LECTRONICªUNITS ! NUMBER OF UNITS ARE COMMONLY USED IN ELECTRONICS

31. SO WE SHALL START BY INTRODUCING SOME OF THEM ,ATER

32. WE WILL BE PUT THESE UNITS TO USE WHEN WE SOLVESOMESIMPLECIRCUITPROBLEMS

33. BUT SINCE ITmS IMPORTANT TO GET TO KNOW THESE UNITS AND ALSO TO BE ABLE TO RECOGNISE THEIR ABBREVIATIONS AND SYMBOLS WE HAVE SUMMARISED THEM IN 4ABLE 0LEASE NOTEØ REQUENCY AND BIT RATE ARE VERY SIMILAR 4HEY BOTH INDICATE THE SPEED AT WHICH A SIGNAL IS TRANSMITTED

34. BUT BIT RATE IS USED FOR DIGITAL SIGNALS WHILE FRE QUENCY IS USED WITH ANALOGUE SIGNALS 'JH 5ZQJDBM BOBMPHVF BOE EJHJUBM TJHOBMT 'JH O FMFDUSPOJD TZTUFN UIBU VTFT CPUI BOBMPHVF BOE EJHJUBM TJHOBMT 4ABLE 3OMEªELECTRICALªQUANTITIESªANDªUNITSªOFªMEASUREMENT 3DUDPHWHU 8QLW $EEUHYLDWLRQ 1RWHV (OHFWULF SRWHQWLDO 9ROW 9 $ SRWHQWLDO RI 9 RQH 9ROW

35. DSSHDUV EHWZHHQ WZR SRLQWV ZKHQ D FXUUHQW RI $ RQH $PS

36. IORZV LQ D FLUFXLW KDYLQJ D UHVLVWDQFH RI : RQH 2KP

37. 1RWH WKDW HOHFWULF SRWHQWLDO LV DOVR VRPHWLPHV UHIHUUHG WR DV HOHFWURPRWLYH IRUFH (0)

38. RU SRWHQWLDO GLIIHUHQFH SG

39. (OHFWULF FXUUHQW $PSHUH $ $ FXUUHQW RI $ IORZV LQ DQ HOHFWULFDO FRQGXFWRU ZKHQ HOHFWULF FKDUJH LV EHLQJ WUDQVSRUWHG DW WKH UDWH RI RXORPE SHU VHFRQG (OHFWULF SRZHU :DWW : 3RZHU LV WKH UDWH RI XVLQJ HQHUJ $ SRZHU RI : RQH :DWW

40. FRUUHVSRQGV WR -RXOH RI HQHUJ EHLQJ XVHG HYHU VHFRQG (OHFWULFDO UHVLVWDQFH 2KP : $Q HOHFWULF FLUFXLW KDV D UHVLVWDQFH RI : ZKHQ D SG VHH DERYH

41. RI 9 LV GURSSHG DFURVV LW ZKHQ D FXUUHQW RI $ LV IORZLQJ LQ LW )UHTXHQF +HUW] +] $ VLJQDO KDV D IUHTXHQF RI +] RQH +HUW]

42. LI RQH FRPSOHWH FFOH RI WKH VLJQDO RFFXUV LQ D WLPH LQWHUYDO RI V RQH VHFRQG

43. %LW UDWH %LWV SHU VHFRQG ESV $ VLJQDO KDV D ELW UDWH RI ELW SHU VHFRQG LI RQH FRPSOHWH ELQDU GLJLW LV WUDQVPLWWHG LQ D WLPH LQWHUYDO RI V (or amp)

44. 52 Everyday Practical Electronics, November 2010 Teach-In 2011 0LEASE NOTEØ 4O AVOID CONFUSION BETWEEN THE SYMBOLS AND THE ABBREVIATIONS THAT WE USE FOR UNITS

45. THE FORMER ARE NORMALLY DISPLAYED IN ITALIC FONT OR EXAMPLE

46. A CAPITAL LETTER 6 IS USED AS BOTH THE ABBREVIATION FOR VOLTAGE AND FOR ITS UNIT SYMBOL THE 6OLT 7HEN USED AS A SYM BOL IN A FORMULA IT IS CONVENTIONALLY SHOWN IN ITALIC AS 7 AND WHEN USED AS SHORTHAND FOR VOLTS IT IS SHOWN IN NORMAL NON ITALIC FONT AS l6m -ULTIPLESªANDª SUB MULTIPLESª 5NFORTUNATELY

47. BECAUSE THE NUMBERS CAN BE VERY LARGE OR VERY SMALL

48. MANY OF THE ELECTRONIC UNITS CAN BE CUMBER SOME FOR EVERYDAY USE OR EXAMPLE

49. THE VOLTAGE PRESENT AT THE ANTENNA OF A MOBILE PHONE COULD BE AS LITTLE AS ONE TEN MILLIONTH OF A VOLT

50. OR 6 #ONVERSELY

51. THE RESISTANCE SEEN AT THE INPUT OF AN AUDIO AMPLIÚER STAGE COULD BE MORE THAN ONE HUNDRED THOUSAND OHMS

52. OR

53. : 4O MAKE LIFE A LOT EASIER WE USE A STANDARD RANGE OF MULTIPLES AND SUB MULTIPLES 4HESE USE A PREÚX LETTER IN ORDER TO ADD A MULTIPLIER TO THE QUOTED VALUE

54. AS SHOWN IN 4ABLE 0LEASE NOTEØ %XPONENT NOTATION IS OFTEN USEFUL WHEN PERFORMING CALCULATIONS USING VERY LARGE OR VERY SMALL NUMBERS 9OU CAN USE EXPONENT NOTATION BY PRESSING THE EXPONENT % OR ENGINEERING %.' BUTTON ON YOUR CALCULATOR #ONVERTINGªTOFROMªMULTIPLESª ANDªSUB MULTIPLES #ONVERTING TO AND FROM MULTIPLES AND SUB MULTIPLES IS ACTUALLY QUITE EASY

55. AS THE FOLLOWING EXAMPLES SHOW %XAMPLE $POWFSU )[ UP L)[ 4O DO THIS YOU JUST NEED TO MOVE THE DECIMAL POINT UISFF PLACES TO THE MFGU 4HIS IS THE SAME AS DIVIDING BY

56. BECAUSE THERE ARE

57. (Z IN K(Z -OVING THE DECIMAL POINT THREE PLACES TO THE LEFT TELLS US THAT

58. (Z K(Z K(Z %XAMPLE $POWFSU : UP .: 4O DO THIS YOU NEED TO MOVE THE DECIMAL POINT TJY PLACES TO THE MFGU 4HIS IS THE SAME AS DIVIDING BY

59. BE CAUSE THERE ARE

60. : IN -:

61. -OVING THE DECIMAL POINT SIX PLACES TO THE LEFT TELLS US THAT

62. : -: %XAMPLE $POWFSU 7 UP N7 4O DO THIS YOU NEED TO MOVE THE DECI MAL POINT UISFF PLACES TO THE SJHIU 4HIS IS THE SAME AS MULTIPLYING BY

64. M6 IN 6 -OVING THE DECIMAL POINT THREE PLACES TO THE RIGHT TELLS US THAT 6 M6 %XAMPLE $POWFSU LCQT UP .CQT 4O DO THIS YOU NEED TO MOVE THE DECI MAL POINT UISFF PLACES TO THE MFGU 4HIS IS THE SAME AS DIVIDING BY

66. KBPS IN -BPS -OVING THE DECIMAL POINT THREE PLACES TO THE LEFT TELLS US THAT

67. KBPS -BPS 0LEASE NOTEØ -ULTIPLYING BY

68. IS EQUIVALENT TO MOVING THE DECIMAL POINT THREE PLACES TO THE RIGHT

69. WHILE DIVIDING BY

70. IS EQUIVALENT TO MOVING THE DECIMAL POINT THREE PLACES TO THE LEFT 3IMILARLY

71. MULTIPLYING BY

72. IS EQUIVALENT TO MOVING THE DECIMAL POINT SIX PLACES TO THE RIGHT

73. WHILE DIVIDING BY

74. IS EQUIVALENT TO MOVING THE DECIMAL POINT SIX PLACES TO THE LEFT 7AVEFORMSªANDªWAVEFORMª MEASUREMENT ! GRAPH SHOWING THE VARIATION OF VOLTAGE OR CURRENT PRESENT IN A CIRCUIT 'JH 4PNF DPNNPO XBWFGPSNT Multiple Exponent notation Prefix Abbreviation Example u1,000,000,000 u Giga G 1.2GHz (1,200 million Hertz) u1,000,000 u Mega M 2.2M: (2.2 million Ohms) u1,000 u Kilo k 4kbs (4,000 bits per second) u1 u None none 220: (220 Ohms) u u Milli m 45mV (0.045 Volts) u u Micro P 33PA (0.000033 Amps) u u Nano n 450nW (0.00000045 Watts) 4ABLE 3OMEªCOMMONªMULTIPLESªANDªSUB MULTIPLES

75. Everyday Practical Electronics, November 2010 53 Teach-In 2011 %XAMPLE XBWFGPSN IBT B GSFRVFODZ PG )[ 8IBU JT UIF QFSJPEJD UJNF PG UIF XBWFGPSN (ERE WE MUST USE THE RELATIONSHIP U G WHERE G (Z (ENCE

76. U S OR MS %XAMPLE XBWFGPSN IBT B QFSJPEJD UJNF PG NT 8IBU JT JUT GSFRVFODZ (ERE WE MUST USE THE RELATIONSHIP G U WHERE U MS OR S (ENCE

77. G (Z !MPLITUDE 4HE AMPLITUDE OR QFBL WBMVF OF A WAVEFORM IS A MEASURE OF THE EXTENT OF ITS VOLTAGE OR CURRENT EXCURSION FROM THE RESTING VALUE USUALLY ZERO 4HE QFBLUPQFBL VALUE FOR A WAVE

78. WHICH IS SYMMETRICAL ABOUT ITS RESTING VALUE

79. IS TWICE ITS PEAK VALUE SEE IG 4HESE UNITS ARE USUALLY MORE CONVEN IENT TO USE WHEN TAKING MEASUREMENTS FROM A WAVEFORM DISPLAY 0ULSEªWAVEFORMS 7HEN DESCRIBING RECTANGULAR AND PULSE WAVEFORMS WE USE A DIFFERENT SET OF PARAMETERS SEE IG 4HESE INCLUDE /N TIME

80. TON 4HIS IS THE TIME FOR WHICH THE PULSE IS PRESENT AT ITS MAXIMUM AMPLITUDE 4HIS IS SOMETIMES REFERRED TO AS THE lNBSL UJNFm .OTE THAT WHEN A PULSE IS NOT PER FECTLYRECTANGULAR IE

81. WHENITTAKESSOME TIME TO CHANGE FROM ONE LEVEL TO THE OTHER

82. WE DEÚNE THE OFF TIME AS THE TIMEFORWHICHTHE PULSE AMPLITUDE REMAINS ABOVE OF ITS MAXI MUM VALUE /FF TIME

83. T/ 4HIS IS THE TIME FOR WHICH THE PULSE IS NOT PRESENT IE

84. ZERO VOLTAGEORCURRENT 4HIS IS SOMETIMES REFERRED TO AS THE lTQBDF UJNFm .OTE THAT

85. WHEN A PULSE IS NOT PER FECTLY RECTANGULAR AND TAKES SOME TIME TO CHANGE FROM ONE LEVEL TO AN OTHER

86. WE DEÚNE THE OFF TIME AS THE TIME FOR WHICH THE PULSE AMPLITUDE FALLS BELOW OF ITS MAXIMUM VALUE 0ULSE PERIOD

87. T 4HIS IS THE TIME FOR ONE COMPLETE CYCLE OF A REPETITIVE PULSE WAVEFORM 4HE PERIODIC TIME IS THUS EQUAL TO THE SUM OF THE ON AND OFF TIMES BUT ONCE AGAIN

88. NOTE THAT THIS IS ONLY VALID IF THE PULSE TRAIN IS REPETITIVE AND IS MEAN INGLESS IF THE PULSES OCCUR AT RANDOM INTERVALS 7HEN A PULSE TRAIN IS NOT PERFECTLY RECTANGULAR

89. THE PULSE PERIOD IS MEAS URED AT THE AMPLITUDE POINTS IS KNOWN AS A WAVEFORM 7AVEFORMS SHOW US HOW VOLTAGE OR CURRENT SIG NALS VARY WITH TIME 4HERE ARE MANY COMMON TYPES OF WAVEFORM ENCOUN TERED IN ELECTRONIC CIRCUITS

90. INCLUDING TJOF OR SINUSOIDAL

91. TRVBSF

92. USJBOHMF

93. SBNQ OR TBXUPPUI WHICH MAY BE EITHER POSITIVE OR NEGATIVE GOING

94. AND QVMTF #OMPLEX WAVEFORMS

95. LIKE SPEECH AND MUSIC

96. USUALLY COMPRISE MANY DIFFERENT SIGNAL COMPONENTS AT DIFFER ENT FREQUENCIES 0ULSE WAVEFORMS ARE OFTEN CATEGORISED AS EITHER REPETITIVE OR NON REPETITIVE THE FORMER COMPRISES A PATTERN OF PULSES THAT REPEATS REGU LARLY

97. WHILE THE LATTER COMPRISES PULSES WHICH EACH CONSTITUTE A UNIQUE EVENT 3OME COMMON WAVEFORMS ARE SHOWN IN IG REQUENCY 4HE FREQUENCY OF A REPETITIVE WAVE FORM IS THE NUMBER OF CYCLES OF THE WAVEFORM WHICH OCCUR IN UNIT TIME IE ONE SECOND REQUENCY IS EXPRESSED IN (ERTZ (Z

98. AND A FREQUENCY OF (Z IS EQUIVALENT TO ONE CYCLE PER SECOND (ENCE

99. IF A VOLTAGE HAS A FREQUENCY OF (Z

100. CYCLES OF IT WILL OCCUR IN EVERY SECOND 0ERIODIC TIME 4HE PERIODIC TIME OR PERIOD OF A WAVEFORM IS THE TIME TAKEN FOR ONE COMPLETE CYCLE OF THE WAVE SEE IG 4HE RELATIONSHIP BETWEEN PERIODIC TIME AND FREQUENCY IS THUS U G OR G U WHERE U IS THE PERIODIC TIME IN S AND G IS THE FREQUENCY IN (Z 'JH 0OF DZDMF PG B TJOFXBWF WPMUBHF TIPXJOH JUT QFSJPEJD UJNF 'JH 0OF DZDMF PG B TJOFXBWF WPMU BHF TIPXJOH JUT QFBL BOE QFBLUPQFBL WBMVFT 0ULSE REPETITION FREQUENCY

101. PRF 4HE PULSE REPETITION FREQUENCY PRF IS THE RECIPROCAL OF THE PULSE PERIOD (ENCE QSG U U/. U/ -ARK TO SPACE RATIO 4HE MARK TO SPACE RATIO OF A PULSE WAVE IS SIMPLY THE RATIO OF THE ON TO OFF TIMES (ENCE 'JH QVMTF XBWFGPSN TIPXJOH mPOn BOE mPGGn UJNFT

102. 54 Everyday Practical Electronics, November 2010 Teach-In 2011 REPLACE THE ENTIRE UNIT IN MUCH THE SAME WAY AS WE WOULD REPLACE A SET OF EXHAUSTED BATTERIES .BSL UP TQBDF SBUJP U/. U/ .OTE THAT

103. FOR A PERFECT SQUARE WAVE THE MARK TO SPACE RATIO WILL BE

104. BECAUSE U/. U/ $UTY CYCLE 4HE DUTY CYCLE OF A PULSE WAVE IS THE RATIO OF THE ON TIME TO THE ON PLUS OFF TIME AND IS USUALLY EXPRESSED AS A PERCENTAGE (ENCE %VUZ DZDMF U/. U/. U/ ¯ U/. U ¯ OR A PERFECT SQUARE WAVE

105. THE DUTY CYCLE WILL BE #ELLS

106. ªBATTERIESªANDªPOWERª SUPPLIES #ELLS AND BATTERIES PROVIDE THE POWER FOR A WIDE RANGE OF PORTABLE AND HAND HELD ELECTRONIC EQUIPMENT 4HERE ARE TWO BASIC TYPES OF CELL QSJNBSZ AND TFDPOEBSZ 0RIMARY CELLS PRODUCE ELECTRICAL ENERGY AT THE EXPENSE OF THE CHEMI CALS FROM WHICH THEY ARE MADE AND ONCE THESE CHEMICALS ARE USED UP

107. NO MORE ELECTRICITY CAN BE OBTAINED FROM THE CELL !N EXAMPLE OF A PRIMARY CELL IS AN ORDINARY 6 !! ALKALINE BATTERY )N SECONDARY CELLS

108. THE CHEMICAL ACTION IS REVERSIBLE 4HIS MEANS THAT THE CHEMICAL ENERGY IS CONVERTED INTO ELECTRICAL ENERGY WHEN THE CELL IS DISCHARGED

109. WHEREAS ELECTRICAL ENERGY IS CONVERTED INTO CHEMI CAL ENERGY WHEN THE CELL IS BEING CHARGED !N EXAMPLE OF A SECONDARY CELL IS A 6 !! NICKEL CADMIUM .I#AD BATTERY )N ORDER TO PRODUCE A BATTERY

110. IN DIVIDUAL CELLS ARE USUALLY CONNECTED IN SERIES WITH ONE ANOTHER

111. AS SHOWN IN IG 4HE VOLTAGE PRODUCED BY A BATTERY WITH N CELLS WILL BE O TIMES THE VOLTAGE OF ONE INDIVIDUAL CELL ASSUM ING THAT ALL OF THE CELLS ARE IDENTICAL URTHERMORE

112. EACH CELL IN THE BATTERY WILL SUPPLY THE SAME CURRENT 3ERIES CONNECTED CELLS ARE OFTEN USED TO FORM BATTERIES OR EXAMPLE

113. THE POPULAR 00

114. 00 AND 00 BATTERIES ARE MADE FROM SIX lLAYEREDm 6 PRIMARY ALKALINE CELLS

115. WHICH ARE EFFECTIVELY CONNECTED IN SERIES ! 6 CAR BAT TERY

116. ON THE OTHER HAND

117. USES SIX 6 LEAD ACID SECONDARY CELLS CONNECTED IN SERIES 7HERE AN ELECTRONIC CIRCUIT DERIVES ITS POWER FROM AN !# MAINS SUPPLY

118. WE SOMETIMES SHOW THE SUPPLY AS A BOX WITH TWO TERMINALS ONE MARKED POSITIVE AND ONE MARKED NEGATIVE 4REATING THE POWER SUPPLY AS A SEPARATE UNIT HELPS KEEP THE CIRCUIT SIMPLE )F THE POWER SUPPLY FAILS WE CAN SIMPLY 'JH 4PNF UZQJDBM DFMMT BOE CBUUFSJFT VTFE JO FMFDUSPOJD FRVJQNFOU 'JH 4ZNCPMT GPS DFMMT BOE CBUUFSJFT 'JH 4FSJFT BSSBOHFNFOU PG DFMMT 'JH CMPDL TDIFNBUJD SFQSFTFOUBUJPO PG UIF QPXFS TVQQMZ JO 'JH 'JH UZQJDBM QPXFS TVQQMZ

119. Everyday Practical Electronics, November 2010 55 Teach-In 2011 0LEASE NOTEØ 7E REFER TO THE OUTPUT VOLTAGE PRO DUCED BY A BATTERY OR A POWER SUPPLY AS AN ELECTROMOTIVE FORCE %- %LEC TROMOTIVE FORCE IS MEASURED IN VOLTS

120. 6 )N CONTRAST

121. WE REFER TO THE VOLTAGE DROP ACROSS AN ELECTRONIC COMPONENT SUCH AS A RESISTOR OR CAPACITOR AS A POTENTIAL DIFFERENCE PD 0OTENTIAL DIFFERENCE IS ALSO MEASURED IN VOLTS 6 4HE BEST WAY TO DISTINGUISH BE TWEEN %- AND PD IS TO REMEMBER THAT %- IS THE lCAUSEm AND PD IS THE lEFFECTm ! TYPICAL POWER SUPPLY WHICH HAS AN !# MAINS INPUT AND $# OUTPUT IS SHOWN IN IG IG SHOWS HOW WE CAN REPRESENT THE POWER SUP PLY USING A SIMPLE CMPDL TDIFNBUJD EJBHSBN .OTE THAT WE HAVE NOT SHOWN ANY SWITCHES

122. FUSES OR INDICATORS IN THIS DIAGRAMØ #HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING 3HORT ANSWER QUESTIONS %XPLAIN THE DIFFERENCE BE TWEENANALOGUEANDDIGITALSIGNALS ,IST THE UNITS USED FOR EACH OF THE FOLLOWING ELECTRICAL QUANTITIES A CURRENT B POTENTIAL C POWER D RESISTANCE E FREQUENCY F BIT RATE %XPLAIN WHAT IS MEANT BY EACH OF THE FOLLOWING ABBREVIATIONS A M6 B K(Z C ! D -(Z E K: F N7 D KBPS !N AMPLIÚER REQUIRES AN INPUT SIGNAL OF 6 %XPRESS THIS IN M6 !N !$# OPERATES AT A BIT RATE OF KBPS %XPRESS THIS IN -BPS ! CURRENT OF Ž! ÛOWS IN A RESISTOR %XPRESS THIS IN M! ! RADIO SIGNAL HAS A FRE QUENCY OF -(Z %XPRESS THIS IN K(Z ! PORTABLE #$ PLAYER USES A BATTERY WHICH HAS FOUR 6 CELLS CONNECTED IN SERIES 7HAT %- DOES THIS BATTERY SUPPLY %XPLAINTHEDIFFERENCEBETWEEN %- AND PD %XPLAIN THE DIFFERENCE BE TWEENPRIMARYCELLSANDSECONDARY CELLS ,ONG ANSWER QUESTIONS IG BELOW SHOWS AN ELEC TRONIC SYSTEM THAT USES BOTH ANALOGUE AND DIGITAL SIGNALS 4AKE A CAREFUL LOOK AT THE DIAGRAM AND SEE IF YOU CAN UNDERSTAND HOW IT WORKS BEFORE ANSWERING THE FOLLOWING QUESTIONS A %XPLAINTHEPURPOSEOFTHESYSTEM B !T WHICH POINTS !

123. # ETC DO THE SIGNALS EXIST IN DIGITAL FORM AND AT WHICH POINTS DO THEY EXIST IN ANALOGUE FORM C 7HAT FORM DO THE SIGNALS HAVE WHEN THEY ARE PRESENT IN THE WIRELESS RADIO LINK 'JH 4FF 2VFTUJPO 'JH 4FF 2VFTUJPO D #AN YOU SUGGEST ANY AD VANTAGES ANDOR DISADVANTAGES OF THE SYSTEM IG SHOWS A WAVE FORM DIAGRAM A 7HAT TYPE OF WAVEFORM IS SHOWN B 7HAT IS THE AMPLITUDE OF THE WAVEFORM C 7HAT IS THE PERIOD OF THE WAVE FORM D 7HAT IS THE REPETITION FRE QUENCY OF THE WAVEFORM E 7HAT IS THE MARK TO SPACE RATIO OF THE WAVEFORM

124. 56 Everyday Practical Electronics, November 2010 Teach-In 2011 2.% OF THE PROBLEMS WITH ELEC TRONICS IS SIMPLY THE AMOUNT OF KIT THAT YOU NEED TO GET STARTED %VEN A BASIC STARTER SET UP COULD RUN IN TO HUNDREDS OF POUNDS SOLDERING IRON

125. HAND TOOLS

126. CIRCUIT BOARD

127. WIRES

128. LEADS

129. COMPONENTS

130. TEST EQUIPMENT q IT ALL ADDS UPØ 4HEREFORE

131. THE lUILDm SECTION OF OUR 4EACH )N SERIES IS GOING TO FOCUS AROUND USING #IRCUIT 7IZARD

132. A REALLY GREAT PIECE OF CIRCUIT SIMULATION SOFT WARE THAT RUNS ON YOUR 7INDOWS 0# )N THIS WAY

133. YOUmLL HAVE ACCESS TO LITERALLY THOUSANDS OF COMPONENTS

134. A FULL RANGE OF lVIRTUAL TEST EQUIPMENTm ALONG WITH REAL TIME SIMULATION AND TOOLS TO HELP YOU ACTUALLY VISUAL ISE THE OPERATION OF YOUR CIRCUITS 4HEREmS ALSO THE ABILITY TO BUILD BREADBOARD CIRCUITS AND CONVERT YOUR CIRCUITS INTO A PRINTED CIRCUIT BOARD 0# DESIGN THAT CAN THEN BE MANUFACTURED 7E REALLY FEEL THAT ITmS THE IDEAL WAY TO GET STARTED WITH ELECTRONICS

135. SO MUCH SO THAT

136. WITH THE NEXT ISSUE OF 1

137. WE WILL GIVE AWAY A GSFF #$ 2/- CONTAINING A lDEMOm VERSION OF THE #IRCUIT 7IZARD 3IMULATION 3TUDENTS OF ELECTRONICS ARE OFTEN CONFUSED BY THE FACT THAT YOU CANmT ACTUALLY SEE WHATmS GOING ON INSIDE A CIRCUIT )N A MECHANICAL MACHINE ITmS EASY TO SEE THINGS MOVING AND WORKING

138. BUT WE HAVE NONE OF THESE VISUAL CLUES WHEN WORKING ON AN ELECTRONIC CIRCUIT #OMPUTER SIMULATION NEATLY OVER COMES THIS PROBLEM BY PROVIDING A VISUAL REPRESENTATION OF WHATmS GOING ON UNDER THE SURFACE 4HIS MIGHT IN CLUDE THE ÛOW OF CURRENT IN WIRES

139. THE VOLTAGE AT VARIOUS POINTS IN A CIRCUIT

140. OR THE CHARGE PRESENT IN A CAPACITOR )N INDUSTRY

141. THE USE OF SOFTWARE FOR SIMULATION

142. DESIGN AND MANUFACTURE OF ELECTRONIC PRODUCTS IS THE NORM )N DEED

143. BEINGABLETOMAKEEFFECTIVEUSEOF SOFTWARE TOOLS IS NOW A KEY SKILL FOR ANY ASPIRINGELECTRONICENGINEERORHOBBYIST ! STANDARD LICENCE FOR #IRCUIT 7IZARD COSTS AROUND | AND CAN BE PURCHASED FROM THE EDITORIAL OFÚCE OF %0% q SEE THE 5+ SHOP ON OUR WEBSITE WWWEPEMAGCOM URTHER INFORMA TION CAN BE FOUND ON THE .EW 7AVE #ONCEPTS WEBSITE WWWNEW WAVE CONCEPTSCOM 4HE DEVELOPER ALSO OF FERS AN EVALUATION COPY OF THE SOFTWARE THE SOFTWARE THAT WILL BE GSFF WITH 1 NEXT MONTH (OWEVER

144. IF YOUmRE SERI OUS ABOUT ELECTRONICS AND WANT TO FOL LOW OUR SERIES

145. THEN A COPY OF #IRCUIT 7IZARD IS A REALLY SOUND INVESTMENT THAT WILL OPERATE FOR DAYS

146. ALTHOUGH IT DOES HAVE SOME LIMITATIONS APPLIED

147. SUCH AS ONLY BEING ABLE TO SIMULATE THE INCLUDED SAMPLE CIRCUITS AND NO ABILITY TO SAVE YOUR CREATIONS

148. THIS IS UILDªnª4HEª#IRCUITª7IZARDªWAY 'JH $JSDVJU 8J[BSE TDSFFOTIPU TIPXJOH UIF VTF PG mWJSUVBM JOTUSVNFOUTn 'JH DBQBDJUPS DIBSHJOH DJSDVJU TIPXJOH DIBSHF CVJMEJOH VQ PO UIF QMBUFT WPMUBHF MFWFMT BOE B HSBQIJDBM QMPU PG WPMUBHF BHBJOTU UJNF

149. Everyday Practical Electronics, November 2010 57 Teach-In 2011 )N THIS INSTALMENT

150. WEmRE GOING TO LOOK AT INSTALLING AND GETTING STARTED WITH #IRCUIT 7IZARD )N FUTURE MONTHS WE WILL BE USING THE SOFTWARE TO IN VESTIGATE THE THEORY AND CIRCUITS THAT YOU WILL MEET IN l,EARNm 7EmLL ALSO DEVELOP ELECTRONIC DEVICES AND USE #IRCUIT 7IZARD TO DESIGN AND PRODUCE 0#S SO THAT YOU CAN MAKE THE REAL THINGØ )NSTALLATION )NSTALLATION OF #IRCUIT 7IZARD IS VERY STRAIGHTFORWARD

151. AND ITmS A SURPRISINGLY SMALL INSTALLATION FOR WHAT IS SUCH A POWERFUL PIECE OF SOFTWARE /UR INSTALL PROCESS TOOK NO MORE THAN QUARTER OF AN HOUR FROM START TO ÚNISH $URING THE INSTALLATION PROCESS YOUmLL BE ASKED TO ENTER A LICENCE KEY WHICH WILL BE SUP PLIED WITH YOUR INSTALL DISC 7HEN YOU RUN #IRCUIT 7IZARD FOR THE ÚRST TIME YOU WILL BE ASKED TO OBTAIN A RELEASE CODE

152. WHICH CAN BE DONE OVER THE lPHONE OR VIA THE DEVELOPERmS WEB SITE WHERE THE RELEASE CODE IS THEN SUB SEQUENTLY E MAILED TO YOU 4HIS NEEDS TO BE DONE WITHIN A DAY WINDOW OR THE SOFTWARE WILL CEASE TO LOAD IRSTªLOOKS 4HE USER INTERFACE IS BOTH CLEAN AND INTUITIVE 4HE MAIN WHITE DRAWING AREA ÚLLS MOST OF THE SCREEN

153. WITH THE STANDARD 7INDOWS MENUS AND TOOLBAR ACROSS THE TOP ! TABBED PANE ON THE RIGHT HAND SIDE OF THE SCREEN PRESENTS A l'ETTING 3TARTEDm MENU

154. WHERE YOU CAN ACCESS VARIOUS SAMPLESTUTORIALS AND GAIN HELP #LICKING THE l'ALLERYm TAB EXPOSES AN EXTENSIVE LIBRARY OF COMPONENTS AND TEST EQUIPMENT 4ABS ON THE FAR LEFT OF THE SCREEN ALLOW YOU TO SEE YOUR CIRCUIT IN VARIOUS DIFFERENT lVIEWSm 4HESE ARE DESIGNED TO HELP YOU SEE WHATmS ACTUALLY GOING ON IN YOUR CIR CUITS BY COLOURING ANDOR ANIMATING THE CIRCUIT DIAGRAM TO SHOW VOLTAGES CURRENTS 4HIS IS A REALLY NIFTY FEATURE

155. AL LOWING YOU TO ACTUALLY SEE ELECTRON ICS IN ACTION 4HERE ARE A NUMBER OF PRESET VIEWS OR YOU CAN CREATE YOUR OWN TO SUIT !LONG THE BOTTOM OF THE SCREEN A ROW OF TABS ALLOWS YOU TO CHANGE BETWEEN DIFFERENT PAGES OF YOUR DESIGN l$RAWINGm IS WHERE YOU WOULD AC TUALLY ENTER AND SIMULATE A CIRCUIT

156. l0# ,AYOUTm IS WHERE YOU WOULD PRODUCE A 0# DESIGN AS WELL AS WORKING WITH VIRTUAL TEST EQUIPMENT AND BREADBOARDS INALLY

157. lILL OF -ATERIALSm GENERATES AN INVENTORY COSTING OF THE COMPONENTS USED IN YOUR CIRCUIT INDINGªYOURªWAYªAROUND Y FAR THE BEST WAY TO GET STARTED WITH #IRCUIT 7IZARD IS TO FOLLOW THE GUIDED TOUR SCREEN VIDEOS AND EX PERIMENT WITH THE SAMPLE CIRCUITS PROVIDED !LL OF THESE ARE DIRECTLY ACCESSIBLE FROM THE l'ETTING 3TARTEDm PAGE IN THE RIGHT HAND PANE CLICK ON 'JH MPHJDCBTFE FMFDUSPOJD EJDF JO mMPHJD WJFXn TIPXJOH EJHJUBM TJHOBM MFWFMT BU FBDI QPJOU JO UIF DJSDVJU 'JH $JSDVJU 8J[BSEnT (BMMFSZ PG DPNQPOFOUT BOE UFTU FRVJQNFOU

158. 58 Everyday Practical Electronics, November 2010 Teach-In 2011 THE l!SSISTANTm TAB IF THE CIRCUIT GALLERY VIEW IS SHOWN 4HE SCREEN VIDEOS EXPLAIN THE BASIC OPERATION OF THE SOFTWARE BUT LACK SOUND

159. WITH ONLY WRITTEN DESCRIPTIONS APPEARING ON THE SCREEN THIS DOES MAKE FOR SLOW PROGRESS )F YOUmRE A CON ÚDENT COMPUTER USER YOU MAY WANT TO JUST JUMP STRAIGHT IN AND EXPLORE OVER ÚFTY SAMPLE CIRCUITS THAT ARE INCLUDED AND GET TO KNOW THE SOFTWARE HANDS ON SOME SIMPLE CIRCUITS THAT WILL BE UN DERPINNED BY THE THEORY COVERED IN OUR l,EARNm SECTION 5NTIL THEN

160. YOU MIGHT LIKE TO GET YOURSELF A COPY OF #IRCUIT 7IZARD AND HAVE A PLAYØ )F YOUmRE RE ALLY KEEN TO GET STUCK IN

161. CHECK OUT OUR 5FBDI*O WEBSITE AT WWW TOOLEYCOUKTEACH IN

162. WHERE YOU CAN DOWNLOAD SOME FURTHER EXAMPLES 'JH $JSDVJU 8J[BSE QSPWJEFT B HPPE TFMFDUJPO PG TUBSUFS NBUFSJBMT 4HE SAMPLE CIRCUITS ARE SPLIT BY COM PLEXITY INTO THREE FOLDERS SIMPLE

163. BASIC AND ADVANCED %ACH OF THESE IS THEN FURTHER DIVIDED INTO SUB CATEGORIES

164. WHICH REALLY SHOWCASE THE EXTENSIVE FEATURES OF THE SOFTWARE 4HE SAMPLE CIRCUITS ARE EXCELLENT AND CONTAIN INSTRUCTIONS ON HOW TO TEST OUT THE CIR CUIT q THEYmRE ALSO REALLY EDUCATIONAL

165. SO YOU MIGHT EVEN LEARN SOMETHING ABOUT ELECTRONICS AS YOU DISCOVER THE SOFTWARE TOOØ )N NEXT MONTHmS INSTALMENT

166. WEmLL BE SHOWING YOU HOW TO ENTER AND TEST :!6%/2-3 ARE USUALLY DIS PLAYED USING AN INSTRUMENT CALLED AN OSCILLOSCOPE 9OU WILL LEARN MORE ABOUT THIS INSTRUMENT LATER IN THE SERIES /SCILLOSCOPES CAN BE STAND ALONE TEST INSTRUMENTS SEE IG OR THEY CAN BE VIRTUAL INSTRUMENTS THAT USE A 0#mS IN BUILT SIGNAL PROCESSING CAPABILITIES EG

167. THE ANALOGUE TO DIGITAL CONVERTER IN A 0# SOUND CARD IG SHOWS A TYPICAL VIRTUAL IN STRUMENT DISPLAY OBTAINED BY USING A SOUNDCARD OSCILLOSCOPE PROGRAM 4HE PROGRAM RECEIVES ITS DATA FROM THE COMPUTERmSSOUNDCARDWITHASAMPLING RATE OF K(Z AND A RESOLUTION OF BITS 4HE DATA SOURCE CAN BE SELECTED BY THE 0#mS OWN SOUND CARD CONTROLS EG

168. MICROPHONE

169. LINE INPUT OR WAVE 4HE FREQUENCY RANGE OF THE INSTRUMENT DEPENDS ON THE PERFORMANCE OF THE COMPUTERmS SOUND CARD

170. BUT IS TYPICALLY ACCURATE OVER THE RANGE (Z TO K(Z 4HE OSCILLOSCOPE ALSO CONTAINS A SIMPLE SIGNAL GENERATOR PRODUCING SINE

171. SQUARE

172. TRIANGLE AND SAWTOOTH WAVEFORMS IN THE FREQUENCY RANGE FROM TO K(Z 4HESE SIGNALS ARE AVAILABLE AT THE SPEAKER OUTPUT OF THE SOUND CARD 4AKE A CAREFUL LOOK AT IG AND USEITTOANSWERTHEFOLLOWINGQUESTIONS A 7HAT TYPE OF WAVEFORM IS SHOWN B 7HAT TOTAL TIME INTERVAL IS DIS PLAYED ON THE SCREEN (INT LOOK AT THE HORIZONTAL SCALE C 7HAT SETTINGS ARE USED FOR THE VERTICAL AND HORIZONTAL SCALES ON THE OSCILLOSCOPE DISPLAY D 7HAT IS THE GREATEST POSITIVE VOLT AGE PRESENT IN THE WAVEFORM SAMPLE E 7HAT IS THE GREATEST NEGATIVE VOLT AGE PRESENT IN THE WAVEFORM SAMPLE F 7HAT IS THE OVERALL PEAK PEAK VOLTAGE OF THE WAVEFORM 'JH 4FF UIF *OWFTUJHBUF RVFTUJPOT 4HEª#IRCUITª7IZARDªWAY )NVESTIGATE 'JH UZQJDBM CFODI PTDJMMPTDPQF

173. Everyday Practical Electronics, November 2010 59 Teach-In 2011 !NSWERSªTOª1UESTIONS !NALOGUE SIGNALS VARY CON TINUOUSLY IN VOLTAGE AND CURRENT WHILST DIGITAL SIGNALS CAN ONLY EXIST IN DISCRETE LEVELS OF VOLTAGE OR CURRENT A !MPERE

174. B 6OLT

175. C 7ATT

176. D /HM

177. E (ERTZ

178. F BITS PER SECOND A MILLIVOLT

179. B KILOHERTZ

180. C MICROAMP

181. D MEGAHERTZ

182. E KILOHM

183. F NANOWATT

184. G KILOBITS PER SECOND M6 -BPS M! K(Z 6 %- IS USED TO DESCRIBE THE OUTPUT VOLTAGE PRODUCED BY A BATTERY OR POWER SUPPLY 0OTENTIAL DIFFERENCE IS USED TO DESCRIBE THE VOLTAGE DROP THAT APPEARS ACROSS A COM PONENT SUCH AS A RESISTOR OR CAPACITOR 0RIMARY CELLS PRODUCE ELEC TRICAL ENERGY FROM A NON REVERSIBLE CHEMICAL REACTION AND MUST BE DIS POSED OF WHEN EXHAUSTED 3ECONDARY CELLS MAKE USE OF A REVERSIBLE CHEMI CAL REACTION AND CAN BE RECHARGED AND USED AGAIN A 7IRELESS DATA LINK BETWEEN COMPUTER SYSTEMS

185. B ! DIGITAL ANALOGUE # ANALOGUE $ ANALOGUE % ANALOGUE DIGITAL

186. C 3INEWAVE RADIO FREQUENCY WITH SUPERIMPOSED MODULATED SIGNAL INFORMATION

187. D $ISADVANTAGES LACK OF SECURITY COM PARED WITH SYSTEMS LINKED BY CABLE

188. MAY SUFFER FROM INTERFERENCE TOFROM OTHER NEARBY WIRELESS SYSTEMS !DVAN TAGES SIMPLE TO INSTALL

189. DOES NOT NEED PERMANENT CABLING A PULSE WAVE

190. B 6

191. C MS

192. D (Z

193. E !MAZE $OWNLOAD A COPY OF THE 3OUNDCARD /SCILLOSCOPE SOFTWARE AND INVESTIGATE THE OPERATION OF THE PROGRAM USING SOME TYPICAL SIGNALS APPLIED TO THE MICROPHONE OR AUXILIARY INPUTS OF A 0# 4HE SOFTWARE IS AVAILABLE FROM #HRISTIAN :EITNITZmS WEBSITE HTTP WWWZEITNITZDE#HRISTIANSCOPE?EN .EXTªMONTH )N NEXT MONTHmS 5FBDI*O WE SHALL BE LOOKING AT RESISTORS AND CA PACITORS%XAMPLESOFTHESETWOPASSIVE COMPONENTS ARE FOUND IN ALMOST EVERY ELECTRONIC CIRCUIT URTHERMORE

194. WHEN USED TOGETHER

195. THESE TWO COMPONENTS FORM THE BASIS OF A WIDE RANGE OF ELEC TRONIC TIMING AND DELAY CIRCUITS 7E SHALL BE INVESTIGATING THE BE HAVIOUR OF THESE CIRCUITS USING #IRCUIT 7IZARD For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/ teach-in www.technobotsonline.com TechnobotsElectronic Mechanical Components With over 5,100 products available to order online, Technobots provides one of the widest range of components for the Shop callers welcome: Technobots Ltd, 60 Rumbridge Street, Totton, Hampshire SO40 9DS Tel: 023 8086 4891 Get our 120 page A4 catalogue free with your next order by quoting 'discount coupon code' EPE05 at the checkout Battery Products Chargers PSU's Opto Electronics Gears, Pulleys Cams Controller Boards Including Arduino Chain sprockets Breakout Boards from Sparkfun Bearings from 1mm bore Switches Relays Projects kits Robotics Wheels LCD displays Pneumatics Shafts Adaptors Tools Cable, Fuses etc.. 160+ dc model motors + speed controllers Passsives, Semiconductors Sensors connectors etc.. Education Accounts W elcome

196. 50 Everyday Practical Electronics, December 2010 Teach-In 2011 By Mike and Richard Tooley 0ARTªª2ESISTORS

197. ªCAPACITORS

198. ª TIMINGªANDªDELAYªCIRCUITS /URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEªª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS

200. ª#HECK

201. ªUILD

205. ªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª )NªLASTªMONTH SªINSTALMENT

206. ª,EARNªPROVIDEDªYOUªWITHªANªINTRODUCTIONªTOªTHEªSIGNALSªTHATªCONVEYªª INFORMATIONªINªELECTRONICªCIRCUITSªANDªTHEªUNITS

207. ªMULTIPLESªANDªSUB MULTIPLESªTHATªAREªUSEDªWHENªMEASURINGª ELECTRICALªQUANTITIESªUILDªFEATUREDªANªINTRODUCTIONªTOª#IRCUITª7IZARD

208. ªSHOWINGªYOUªHOWªTOªINSTALLªTHEªSOFT WAREªANDªUSEªAªVIRTUALªTESTªINSTRUMENTªWHILEªOURªPRACTICALªSECTIONS

209. ª)NVESTIGATEªANDª!MAZE

210. ªPROVIDEDªYOUª WITHªANªOPPORTUNITYªTOªGETªTOªGRIPSªWITHªANªOSCILLOSCOPEªBASEDªONªAª0#ªSOUNDCARD *

211. AND RESISTANCE

212. 3

213. IN A CIRCUIT SEE IG IS 7 * ¯ 3 WHERE 7 IS THE VOLTAGE IN 6

214. * IS THE CURRENT IN ! AND 3 IS THE RESIST ANCE IN :

215. %XAMPLE ! CURRENT OF M! ÛOWS IN A : RESISTOR 7HAT POTENTIAL DIFFERENCE APPEARS ACROSS THE RESISTOR ROM /HMmS ,AW 7 * ¯ 3 ¯ 6 .OTE THAT M! IS THE SAME AS ! 7($+,1 $ %52$'%$6(' ,1752'87,21 72 (/(7521,6 , . THIS PART OF 4EACH )N WE WILL INTRODUCE YOU TO RESISTORS

216. CAPACI TORS

217. TIMING AND DELAY CIRCUITS 7E WILL ALSO USE #IRCUIT 7IZARD TO INVES TIGATE /HMmS ,AW AS WELL AS ÚNDING OUT WHAT HAPPENS IN A CIRCUIT WHEN A CAPACITOR IS CHARGED AND DISCHARGED ,EARN APPEAR ACROSS A RESISTANCE OF : WHEN A CURRENT OF ! ÛOWS IN IT 2ESISTANCE CAN BE THOUGHT OF AS AN OPPOSITION TO THE ÛOW OF ELECTRIC CURRENT 4HE AMOUNT OF CURRENT THAT WILL ÛOW IN A CIRCUIT WHEN A GIVEN ELECTROMOTIVE FORCE %- IS APPLIED TO IT IS INVERSELY PROPORTIONAL TO ITS RESISTANCE )N OTHER WORDS

218. THE LARGER THE RESISTANCE

219. THE GREATER THE OPPOSI TION TO CURRENT ÛOW WHEN AN %- IS APPLIED /HM SªLAW /HMmS LAW TELLS US THAT THE RELA TIONSHIP BETWEEN VOLTAGE

220. 7

221. CURRENT

222. 2ESISTORS ROM LAST MONTHmS 4EACH )N

223. YOU SHOULD RECALL THAT VOLTAGE IS SPECI ÚED IN VOLTS 6

224. CURRENT IN AMPS ! AND RESISTANCE IN OHMS : ! POTENTIAL DIFFERENCE OF 6 WILL worldmagsworldmags worldmags

225. Everyday Practical Electronics, December 2010 51 Teach-In 2011 %XAMPLE 7HAT CURRENT WILL ÛOW WHEN A : RESISTOR IS CONNECTED TO A 6 BATTERY 2EARRANGING THE FORMULA TO MAKE * THE SUBJECT GIVES 4YPESªOFªRESISTOR 6ARIOUS TYPES OF ÚXED

226. PRESET AND VARIABLE RESISTOR ARE FOUND IN ELEC TRONIC CIRCUITS

227. INCLUDING CARBON ÚLM

228. METAL ÚLM

229. AND WIREWOUND TYPES

230. SEE IG 2ESISTORS HAVE A WIDE VARIETY OF APPLICATIONS IN ELECTRONIC CIRCUITS

231. WHERE THEY ARE USED FOR DETERMINING THE VOLTAGES AND CURRENTS IN CIRCUITS

232. AS lLOADSm TO CONSUME POWER

233. AND IN PRESET AND VARIABLE FORM FOR MAKING ADJUSTMENTS FOR EXAMPLE

234. VOLUME AND TONE CONTROLS 4HE TERMS POTENTIOMETER AND VARIABLE RESISTOR ARE OFTEN USED INTERCHANGEABLY (OWEVER

235. STRICTLY SPEAKING

236. PRESET AND VARIABLE RESIS TORS HAVE ONLY TWO TERMINALS WHILE POTENTIOMETERS EITHER PRESET OR ROTARY TYPES HAVE THREE TERMINALS .OTE ALSO THAT A PRESET OR VARIABLE POTENTIOMETER CAN BE USED AS A VARI ABLE RESISTOR BY SIMPLY IGNORING ONE OF ITS END TERMINALS

237. OR BY CONNECTING ITS MOVING CONTACT TO ONE OF ITS OUTER TERMINALS 4YPICAL CIRCUIT SYMBOLS FOR VARIOUS TYPES OF RESISTOR ARE SHOWN IN IG 4HE SPECIÚCATIONS FOR A RESISTOR USUALLY INCLUDE THE VALUE OF RESISTANCE EXPRESSED IN :

238. K: OR -:

239. THE ACCURACY OR TOLER ANCE OF THE MARKED VALUE QUOTED AS THE MAXIMUM PERMISSIBLE PERCENTAGE DEVIATION FROM THE MARKED 'JH 7BSJPVT UZQFT PG SFTJTUPS JODMVEJOH ÜYFE QSFTFU BOE WBSJBCMF UZQFT %XAMPLE ! CURRENT OF M! ÛOWS IN A RE SISTOR WHEN IT IS CONNECTED TO A 6 POWER SUPPLY 7HAT IS THE VALUE OF THE RESISTANCE 2EARRANGING THE FORMULA TO MAKE 3 THE SUBJECT GIVES .OTE THAT M! IS THE SAME AS ! 'JH TJNQMF DJSDVJU JO XIJDI B CBUUFSZ TVQQMJFT DVSSFOU UP B SFTJTUPS 'JH $JSDVJU TZNCPMT VTFE GPS SFTJTUPST 9 , 5 P$$ 9 5 , : : : N: worldmagsworldmags worldmags

240. 52 Everyday Practical Electronics, December 2010 Teach-In 2011 VALUE

241. AND THE POWER RATING WHICH MUST BE EQUAL TO

242. OR GREATER THAN

243. THE MAXIMUM EXPECTED POWER DIS SIPATION IXEDªRESISTORS IXED RESISTORS ARE AVAILABLE IN SEVERAL SERIES OF lPREFERREDm VALUES

244. SEE 4ABLE 4HE NUMBER OF VALUES PROVIDED WITH EACH SERIES IE

245. AND IS DETERMINED BY THE TOLER ANCE INVOLVED )N ORDER TO COVER THE FULL RANGE OF RESISTANCE VALUES USING RESISTORS HAV ING A ‰ TOLERANCE

246. IT IS NECESSARY TO PROVIDE SIX BASIC VALUES KNOWN AS THE % SERIES -ORE VALUES ARE REQUIRED IN A SERIES THAT OFFERS A TOLERANCE OF ‰

247. AND CONSEQUENTLY THE % SERIES PROVIDES TWELVE BASIC VALUES 4HE % SERIES FOR RESISTORS OF ‰ TOLERANCE PROVIDES BASIC VALUES AND

248. AS WITH THE % AND % SERIES

249. DECADE MULTIPLES IE

250. ¯

251. ¯

252. ¯

253. ¯K

254. ¯K

255. ¯K AND ¯- OF THE BASIC SERIES ! FURTHER SERIES % PROVIDES FOR RESIS TORS WITH A TOLERANCE OF ‰ #ARBON AND METAL OXIDE RESISTORS ARE NORMALLY MARKED WITH COLOUR CODES THAT INDICATE THEIR VALUE AND TOLER ANCE 3EE IG AND IG FOR THE COLOUR CODES 2ELATIONSHIP BETWEEN VOLTAGE

256. CURRENT AND POWER 4HE POWER

257. 1

258. DISSIPATED IN A RE SISTOR IS EQUIVALENT TO THE PRODUCT OF VOLTAGE

259. 7

260. AND CURRENT

261. * 4HUS 1 *7 WHERE 1 IS THE POWER IN 7

262. * IS THE CURRENT IN ! AND 7 IS THE VOLT AGE IN 6 7E CAN COMBINE THIS RELATIONSHIP WITH THE /HMmS LAW EQUATION THAT WE MET EARLIER IN ORDER TO ARRIVE AT THE FOLLOWING USEFUL EXPRESSIONS %XAMPLE 7HAT POWER IS DISSIPATED IN A RE SISTOR OF K: WHEN A VOLTAGE OF 6 APPEARS ACROSS IT 5SING THE PREVIOUS FORMULA GIVES 4ABLEªª4HEª%

263. ª%ªANDª%ªSERIESªOFªPREFERREDªRESISTORªVALUES 'JH 'PVSCBOE SFTJTUPS DPMPVS DPEF 'JH 'JWFCBOE SFTJTUPS DPMPVS DPEF

264. 3 ,9 , ,5 , 5u 9 9 3 ,9 9 5 5 u AND Series of preferred values Values available E6 1.0, 1.5, 2.2, 3.3, 4.7, 6.8 E12 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 E24 1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1 10% 9 3 5 : worldmags worldmags

265. Everyday Practical Electronics, December 2010 53 Teach-In 2011 CHARGE 4HEY ARE WIDELY USED IN POWER SUPPLIES WHERE THEY ACT AS lRESERVOIRSm FOR CHARGE AND ALSO IN MANY TIMING AND WAVE SHAPING CIRCUITS #APACITORS WILL PASS ALTERNATING CURRENTS

266. BUT THEY WILL lBLOCKm DIRECT CURRENT ONCE CHARGED 4HEY ARE THUS USED FOR COUPLING SIGNALS WHICH ARE !# IN AND OUT OF AMPLIÚER STAGES 4HE SPECIÚCATIONS FOR A CAPACITOR USUALLY INCLUDE THE VALUE OF CAPACI TANCE EXPRESSED IN

268. N OR P

269. THE ACCURACY OR TOLERANCE OF THE MARKED VALUE QUOTED AS THE MAXIMUM PER MISSIBLE PERCENTAGE DEVIATION FROM THE MARKED VALUE

270. THE VOLTAGE RATING WHICH MUST BE EQUAL TO

271. OR GREATER THAN

272. THE MAXIMUM EXPECTED VOLTAGE APPLIED TO THE CAPACITOR #APACITORS ARE USUALLY AVAILABLE WITH VALUES IN THE % SERIES SEE 4ABLE 0LEASE NOTEØ ,ARGE VALUE CAPACITORS OFTEN USE A CHEMICAL DIELECTRIC MATERIAL

273. AND THEY REQUIRE THE APPLICATION OF A $# POLARISINGª VOLTAGE IN ORDER TO WORK #APACITORS #APACITORS STORE ENERGY IN THE FORM OF AN ELECTRIC ÚELD 7HEN A POTENTIAL DIFFERENCE IS APPLIED TO TWO CONDUCT ING PLATES AN ELECTRIC CHARGE WILL AP PEAR ON THE PLATES AND AN ELECTRIC ÚELD WILL APPEAR BETWEEN THE PLATES 4HE ÚELD CAN BE CONCENTRATEDINTENSIÚED BY PLACING AN INSULATING MATERIAL SUCH AS POLYESTER ÚLM

274. MICA OR A CERAMIC MATERIAL BETWEEN THE PLATES 4HIS MA TERIAL IS KNOWN AS A DIELECTRIC

275. AND ITS ELECTRICAL PROPERTIES HELP TO INCREASE THE CAPACITANCE OF THE COMPONENT SEE IG #APACITORS PROVIDE US WITH A MEANS OF STORING AND CONSERVING ELECTRIC 'JH 7BSJPVT UZQFT PG DBQBDJUPS JODMVEJOH ÜYFE QSFTFU BOE WBSJBCMF UZQFT 'JH #BTJD BSSBOHFNFOU PG B QBSBMMFM QMBUF DBQBDJUPS 'JH 4ZNCPMT VTFE GPS DBQBDJUPST worldmagsworldmags worldmags

276. 54 Everyday Practical Electronics, December 2010 Teach-In 2011 PROPERLY 4HIS VOLTAGE MUST BE APPLIED WITH THE CORRECT POLARITY INVARIABLY THIS IS CLEARLY MARKED ON THE CASE OF THE CAPACITOR WITH A POSITIVE SIGN OR NEGATIVE q SIGN OR A COLOURED STRIPE OR OTHER MARKING AILURE TO OBSERVE THE CORRECT POLARITY CAN RESULT IN OVER HEATING

277. LEAKAGE

278. AND EVEN A RISK OF EXPLOSIONØ 2ELATIONSHIP BETWEEN CHARGE

279. VOLTAGE AND CAPACITANCE 4HE QUANTITY OF ELECTRIC CHARGE

280. 2

281. THAT CAN BE STORED IN THE ELECTRIC ÚELD BETWEEN THE CAPACITOR PLATES IS PROPOR TIONAL TO THE APPLIED VOLTAGE

282. 7

283. AND THE CAPACITANCE

284. $

285. OF THE CAPACITOR 4HUS OF CAPACITANCE

286. $

287. AND THE SQUARE OF THE APPLIED VOLTAGE

288. 7 4HUS

289. TO STORE A LARGE AMOUNT OF ENERGY WE NEED A CORRESPONDINGLY LARGER VALUE OF CA PACITANCE FOR A GIVEN VALUE OF CHARGING VOLTAGE 4HE FOLLOWING RELATIONSHIP APPLIES 8 • $ 7 WHERE $ IS THE VALUE OF CAPACITANCE IN

290. 7 IS THE CAPACITOR VOLTAGE

291. AND 8 IS THE STORED ENERGY IN JOULES %XAMPLE $ETERMINE THE CHARGE STORED IN A CAPACITOR WHEN IT IS CHARGED TO A POTENTIAL OF 6 4HE STORED ENERGY WILL BE GIVEN BY PARTICULARLY IF THEY ARE HIGH VOLTAGE TYPES UNTIL YOU ARE CERTAIN THAT THE CAPACITORS ARE FULLY DISCHARGED 3OME CIRCUITS INCORPORATE lBLEEDm RESISTORS TO SAFELY DISCHARGE LARGE VALUE CAPACITORS WHEN THE EQUIPMENT IN WHICH THEY ARE USED HAS BEEN SWITCHED OFF # 2ªCIRCUITSª CHARGEªANDª DISCHARGE %ARLIER

292. WE MENTIONED THAT A CA PACITOR IS A DEVICE FOR STORING ELECTRIC CHARGE 4HIS CHARGE CAN BE STORED IN A CAPACITOR BY CONNECTING IT TO A BATTERY OR POWER SUPPLY VIA A SERIES RESISTOR

293. WHICH SUPPLIES CURRENT FOR CHARGING ,ATER

294. THE STORED CHARGE CAN BE DRAINED AWAY BY CONNECTING A RESISTOR IN PARAL LEL WITH THE CAPACITOR !FTER A PERIOD OF TIME THERE WILL THEN BE NO CHARGE REMAINING IN THE CAPACITOR 4HE TIME THAT IT TAKES TO CHARGE AND DISCHARGE A CAPACITOR DEPENDS ON THE VALUES OF CAPACITANCE AND RESISTANCE

295. AND THIS MAKES CAPACITORS IDEAL FOR USE IN TIMING AND DELAY CIRCUITS ECAUSE THIS IS SO IMPORTANT

296. ITmS WORTH LOOKING AT THIS IN A LITTLE MORE DETAIL 3IMPLE CHARGING AND DISCHARGING ARRANGEMENTS ARE SHOWN IN IG )N THE CHARGING ARRANGEMENT SHOWN IN IGA

297. THE CAPACITOR IS INITIALLY UNCHARGED AND CURRENT WILL FLOW AND CHARGE WILL BUILD UP INSIDE THE CAPACITOR

298. QUICKLY AT ÚRST AND THEN MORE SLOWLY !S THE CAPACITOR BECOMES CHARGED

299. THE CAPACITOR VOLTAGE 7# WILL INCREASE UNTIL IT EVENTUALLY BECOMES CLOSE

300. BUT NEVER QUITE EQUAL

301. TO THE VOLTAGE OF THE SUPPLY 73 !T THAT POINT WHEN 7# IS APPROXIMATELY EQUAL TO 73 WE SAY THAT THE CAPACITOR IS FULLY CHARGED 4 9 WHERE 2 IS THE CHARGE IN COULOMBS

302. $ IS THE CAPACITANCE IN FARADS

303. AND 7 IS THE POTENTIAL DIFFERENCE IN VOLTS %XAMPLE $ETERMINE THE CHARGE STORED IN A CAPACITOR WHEN IT IS CHARGED TO A POTENTIAL OF 6 4HE CHARGE STORED WILL BE GIVEN BY %NERGYªSTORAGE ! CHARGED CAPACITOR ACTS AS A RESER VOIR FOR CHARGE AND THE STORED ENERGY CAN BE PUT TO GOOD USE SOME TIME LATER 4HE AMOUNT OF ENERGY STORED IN A CAPACITOR DEPENDS ON THE PRODUCT 'JH DBQBDJUPS DIBSHJOHEJTDIBSHJOH BSSBOHFNFOU 0LEASE NOTEØ 4HE ENERGY STORED IN A CAPACITOR IS PROPORTIONAL TO THE SQUARE OF THE PO TENTIAL DIFFERENCE BETWEEN ITS PLATES 4HUS

304. IF THE POTENTIAL DIFFERENCE IS DOUBLED THE ENERGY STORED WILL IN CREASE BY A FACTOR OF FOUR ,IKEWISE

305. IF THE POTENTIAL DIFFERENCE INCREASES BY A FACTOR OF TEN

306. THE STORED ENERGY WILL INCREASE BY A FACTOR OF 0LEASE NOTEØ ! CHARGED CAPACITOR CAN REMAIN IN A PARTIALLY CHARGED STATE FOR A VERY LONG TIME IF THERE IS NO PATH FOR THE STORED CHARGE TO DRAIN AWAY )TmS THEREFORE IMPORTANT TO AVOID WORKING ON A CIR CUIT THAT USES LARGE VALUE CAPACITORS : ò 9 ò î î î î î - 4 9 î î î î PP worldmagsworldmags worldmags

307. Everyday Practical Electronics, December 2010 55 Teach-In 2011 /NCE AGAIN

308. THE SPEED AT WHICH THE CAPACITOR BECOMES DISCHARGED DEPENDS ON THE TIMEªCONSTANT

309. 5

310. OF THE CIRCUIT OR OUR DISCHARGING CIRCUIT THE TIME CONSTANT IS ALSO GIVEN BY 5 $ ¯ 3 !SBEFORE

311. YOUMIGHTNOWBEWONDER ING HOW LONG IT TAKES TO GVMMZ DISCHARGE THE CAPACITOR 4HE TRUE ANSWER IS THAT THECAPACITORVOLTAGENEVERQUITEREACH ES 6

312. EVEN IF YOU WAIT FOR A VERY LONG TIME (OWEVER

313. IT DOES GET CLOSER AND CLOSER TO 6

314. AND FOR THIS REASON WE SAY THAT THE CAPACITOR IS FULLY DISCHARGED AFTER A TIME INTERVAL EQUAL TO ÚVE TIMES THE TIME CONSTANT 5 OR $3 %XAMPLE ! $3 CIRCUIT CONSISTS OF $ AND 3 -: A 7HAT IS THE TIME CONSTANT OF THE CIRCUIT B )F THE CAPACITOR IS INITIALLY UN CHARGED

315. HOW LONG WILL IT TAKE TO FULLY CHARGE THE CAPACITOR A 4HE TIME CONSTANT IS GIVEN BY 5 $3 ¯ -: SECONDS .OTE THAT IF WE WORK IN AND -: THE TIME CONSTANT WILL BE EXPRESSED DIRECTLY IN SECONDS B 4HE CAPACITOR WILL BE APPROXI MATELY FULLY CHARGED AFTER 5 OR ¯ OR SECONDS 0LEASE NOTEØ 4HE VOLTAGE ACROSS THE PLATES OF A CHARGINGCAPACITORGROWSEXPONENTIALLY NOT LINEARLYØ AT A RATE DETERMINED BY THE TIME CONSTANT OF THE CIRCUIT #ON VERSELY

316. THEVOLTAGEACROSSTHEPLATESOFA DISCHARGING CAPACITOR DECAYS EXPONEN TIALLY NOTLINEARLYØ ATARATEDETERMINED BY THE TIME CONSTANT OF THE CIRCUIT ! GRAPH SHOWING HOW THE CAPACITOR VOLTAGE 7# INCREASES WITH TIME IS SHOWNINIG4HISGRAPHISKNOWN AS AN EXPONENTIALªGROWTH CURVE 4HE SPEED AT WHICH THE CAPACITOR BECOMES CHARGED DEPENDS ON THE TIME CONSTANT

317. 5

318. OF THE CIRCUIT 4HIS IS THE PRODUCT OF THE CAPACITANCE

319. $

320. AND THE CHARGING RESISTANCE

321. 3 (ENCE 5 $ ¯ 3 WHERE $ IS THE VALUE OF CAPACITANCE IN

322. 3 IS THE RESISTANCE IN :

323. AND 5 IS THE TIME CONSTANT IN SECONDS 9OU MIGHT NOW BE WONDERING HOW LONG IT TAKES TO GVMMZ CHARGE THE CAPACI TOR 4HE TRUE ANSWER IS THAT THE CAPACI TOR VOLTAGE NEVER QUITE REACHES THE SUP PLY VOLTAGE

324. EVEN IF YOU WAIT FOR A WFSZ LONG TIME (OWEVER

325. IT DOES GET CLOSER AND CLOSER TO IT

326. AND FOR THIS REASON WE SAY THAT THE CAPACITOR IS FULLY CHARGED AFTER A TIME INTERVAL EQUAL TO ÚVE TIMES THE TIME CONSTANT 5 OR $3 )NTHEDISCHARGINGARRANGEMENTSHOWN INIGB

327. THECAPACITORISINITIALLYFULLY CHARGED AND CURRENT WILL ÛOW WHILE THE CHARGEINSIDETHECAPACITORDECAYSAWAY !S THE CAPACITOR BECOMES DISCHARGED

328. THE CAPACITOR VOLTAGE 7# WILL DECREASE UNTIL IT EVENTUALLY BECOMES CLOSE

329. BUT NEVER QUITE EQUAL

330. TO ZERO 6 !T THAT POINT WHEN 7# IS APPROXIMATELY EQUAL TO 6

331. WE SAY THAT THE CAPACITOR IS FULLY DISCHARGED ! GRAPH SHOWING HOW THE CAPACITOR VOLTAGE 7# DECREASES WITH TIME IS SHOWN IN IG 4HIS GRAPH IS KNOWN AS AN EXPONENTIALªDECAY CURVE 'JH (SBQI PG DBQBDJUPS WPMUBHF BHBJOTU UJNF GPS UIF DIBSHJOH DJSDVJU 'JH (SBQI PG DBQBDJUPS WPMUBHF BHBJOTU UJNF GPS UIF EJTDIBSHJOH DJSDVJU Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofﬁce of EPE – see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com) for a ‘special offer’. Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com.The developer also offers an evaluation copy of the software that will operate for 30 days, although it does have some limitations applied, such as only being able to simulate the included sample circuits and no ability to save yourcreations,thisisthesoftwarethat is free with EPE this month. However, if you’re serious about electronics and want to follow our series, then a full copy of Circuit Wizard is a really sound investment. Virtually fully discharged worldmagsworldmags worldmags

332. 56 Everyday Practical Electronics, December 2010 Teach-In 2011 ,. 4()3 MONTHmS l,EARNm SECTION WEmVE INTRODUCED YOU TO THE BASICS OF RESISTORS AND CAPACITORS !LMOST ALL ELECTRONIC CIRCUITS WILL CONTAIN ONE OR BOTH OF THESE TYPES OF COMPONENTS

333. SO ITmS REALLY IMPORTANT THAT WE UNDERSTAND WHAT THEY DO AND HOW THEY WORK %LECTRONICS TEXT BOOKS OFTEN HAVE LENGTHY AND CONFUSING EXPLANATIONS WITH LOTS OF MATHEMATICAL FORMULAE (OWEVER

334. THE BEST WAY TO REALLY GET TO GRIPS WITH WHATmS GOING ON IS TO EXPERIMENT WITH SOME SIMPLE CIR CUITS 7E ARE GOING TO LOOK AT A FEW OF THE SAMPLE CIRCUITS INCLUDED WITH #IRCUIT 7IZARD

335. AS WELL AS GIVING YOU SOME NEW CIRCUITS TO ENTER AND TRY OUT FOR YOURSELF /HM Sª,AWªINªPRACTICE 4O START WITH

336. WEmLL HAVE A LOOK AT /HMmS ,AW IN PRACTICE /PEN THE l/HMmS ,AWm SAMPLE CIRCUIT FROM THE !SSISTANT PANEL ON THE RIGHT HAND SIDE OF THE SCREEN BY SELECTING l3AMPLE #IRCUITSm

337. THEN l%LEMENTARY #IRCUITSm AND SCROLLING DOWN TO THE l%LECTRICAL 4HEORYm SECTION 4HE CIRCUIT SEE IG IS ABOUT AS SIMPLE AS IT COMES WITH A POWER SOURCE A 6 00 BATTERY AND A VARIABLE RESISTOR 7E ALSO HAVE TWO MULTIMETERS ONE TO SHOW THE VOLT AGE ACROSS THE RESISTOR AND ONE TO SHOW THE CURRENT ÛOWING THROUGH IT 3IMULATION 0RESS THE PLAY BUTTON FOUND ON THE TOOLBAR TO ACTIVATE THE SIMULA TION 9OU SHOULD SEE VALUES APPEAR ING ON THE MULTIMETERS .OW TRY CHANGING THE VALUE OF THE VARIABLE RESISTOR 62 BY CLICKING ON THE END OF THE SHAFT q THE MOUSE POINTER WILL CHANGE TO A POINTED ÚNGER WHEN YOUmRE IN THE RIGHT PLACE 9OUmLL THEN BE PRESENTED WITH A VIRTUAL KNOB THAT YOU CAN TURN TO THE DESIRED VALUE .OTICE THAT AS YOU INCREASE THE RESISTANCE

338. THE CURRENT FLOWING THROUGH IT REDUCES AND WJDF WFSTB .OTE THAT THE READINGS FOR CURRENT ARE IN MILLIAMPS M! 4O TRY OUT THE THEORY THAT WE INTRO DUCED

339. CHECK THE VALUES FOR VOLTAGE AND CURRENT WHEN THE VARIABLE RESIS TOR IS AT

340. AND K

341. AND CHECK THAT THEY OBEY /HMmS LAW #HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING %XPLAIN BRIEÛY WHAT IS MEANT BY RESISTANCE 7HAT UNITS ARE USED FOR RESISTANCE AND WHAT SYMBOL IS USED TO DENOTE THESE UNITS %XPLAIN BRIEÛY WHAT IS MEANT BY CAPACITANCE 7HAT UNITS ARE USED FOR CAPACITANCE AND WHAT SYMBOL IS USED TO DENOTE THESE UNITS ! CURRENT OF ! ÛOWS IN A : RESISTOR 7HAT POTENTIAL DIFFERENCE APPEARS ACROSS THE RESISTOR 7HAT CURRENT WILL ÛOW WHEN A : RESISTOR IS CONNECTED TO A 6 BATTERY ! CURRENT OF M! ÛOWS IN A RESISTOR WHEN IT IS CONNECTED TO A 6 POWER SUPPLY 7HAT IS THE VALUE OF THE RESISTANCE ! VOLTAGE DROP OF 6 APPEARS ACROSS A : RESISTOR 7HAT POWER IS DISSIPATED IN THE RESISTOR ! RESISTOR IS RATED AT :

342. 7 7HAT IS THE MAXIMUM VOLT AGE THAT CAN BE SAFELY APPLIED TO THIS RESISTOR ! CAPACITOR IS CHARGED TO A POTENTIAL OF 6 7HAT CHARGE IS PRESENT 'JH 4FF RVFTUJPO ! CHARGE OF # IS HELD IN A N CAPACITOR 7HAT POTENTIAL AP PEARSACROSSTHEPLATESOFTHECAPACITOR ! CHARGE OF # IS TO BE PLACED ON THE PLATES OF A CAPACITOR OF N 7HAT VOLTAGE IS NEEDED TO DO THIS ! RESISTANCE OF K: IS CON NECTED TO A CAPACITOR OF 7HAT IS THE TIME CONSTANT OF THIS CIRCUIT AND HOW LONG WILL IT TAKE FOR THE CAPACITOR TO BECOME APPROXIMATELY FULLY CHARGED 7HAT COMPONENTS ARE REPRE SENTED BY THE CIRCUIT SYMBOLS SHOWN IN IG 7HAT TYPE OF COMPONENT IS SHOWN IN IG 'JH 4FF RVFTUJPO ªªUILDªn ª ! RESISTOR IS MARKED WITH THE FOL LOWING COLOURED BANDS BROWN

343. BLACK

344. ORANGE

345. SILVER 7HAT IS THE VALUE OF THE RESISTOR AND WHAT IS ITS TOLERANCE ! RESISTOR OF : AT ‰ IS REQUIRED 7HAT SHOULD BE THE COLOUR CODE FOR THIS COMPONENT For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/ teach-in worldmagsworldmags worldmags

346. Everyday Practical Electronics, December 2010 57 Teach-In 2011 #APACITORSªINªACTION .OW WEmLL TAKE A LOOK AT CAPACITORS IN ACTION /PEN l#APACITOR #HARGINGm BY SELECTING 3AMPLE #IRCUITS

347. THEN ªªªªªªª4HEª#IRCUITª7IZARDªWAY 'JH 5IF 0INnT -BX TBNQMF DJSDVJU ASIC #IRCUITS IN THE !SSISTANT SEE IG 7HEN THE ÚLE OPENS IT WILL START OFF IN l0# ,AYOUTm VIEW

348. WHICH SHOWS A VIRTUAL REPRESENTATION OF THE 'JH 5IF DBQBDJUPSDIBSHJOH TBNQMF DJSDVJU #ALCULATE THE TIME CONSTANT FOR THE CIRCUIT USING THE VALUES OF $ AND 3 AND THEN

349. USING A RULER

350. DRAW A VERTICAL LINE UP FROM THAT VALUE ON THE GRAPH FROM THE POINT AT WHICH IT STARTED TO CHARGE AND READ OFF THE VOLTAGE AT THIS POINT $OES IT AGREE WITH WHAT YOU WOULD EXPECT 4HE LAST SAMPLE CIRCUIT THAT WEmLL LOOK AT IS A PRACTI CAL APPLICATION OF CHARGING A CAPACITOR /PEN l4RANSISTOR 4IMERm FROM l3AMPLE #IRCUITSm FOUND UNDER lASIC #IRCUITSm

351. l'ENERALm 4HE CIRCUIT USES A CAPACITOR TO CREATE A TIME DELAY BEFORE THE BULB IS IL LUMINATED )T DOES THIS BY USING A PAIR OF TRANSISTORS ACTING LIKE A SWITCH 7EmLL BE LOOKING AT TRANSISTORS IN MORE DETAIL IN SUBSEQUENT 4EACH )N EDITIONS CIRCUIT

352. ALONG WITH AN OSCILLOSCOPE SHOWING THE VOLTAGE ACROSS A CAPACITOR # 3TART SIMULATING THE CIRCUIT AND KEEP AN EYE ON THE lDOTm ON THE OSCIL LOSCOPE SCREEN 7ATCH HOW IT RISES AS THE CAPACITOR CHARGES /NCE THE TRACE HAS LEVELLED OFF

353. ÛICK THE SWITCH TO START DISCHARGING THE CAPACITOR AND AGAIN WATCH THE OSCILLOSCOPE SCREEN TO SEE HOW THE VOLTAGE FALLS WITH TIME #IRCUITªDIAGRAM 4O SEE THE SCHEMATIC LAYOUT FOR THE CIRCUIT

354. SWITCH TO THE l#IRCUIT $IAGRAMm VIEW USING THE TABS ON THE BOTTOM OF THE SCREEN 3TART THE SIMU LATION AGAIN AND CONTROL THE SWITCH TO ALLOW THE CAPACITOR TO CHARGE AND DISCHARGE 4HE VOLTAGE ACROSS THE CAPACITOR IS THEN PLOTTED ON THE GRAPH IN REAL TIME #IRCUIT 7IZARD ALSO DEMONSTRATES THE CHARGE BUILDING UP ON THE PLATES OF THE CAPACITOR WITH BLUERED lPLUSSESm AND lMINUSESm )N l,EARNm WE SHOWED HOW TO CALCU LATE THE TIME PERIOD USING THE FORMULA 5 $3 WHICH IS WHEN THE VOLTAGE ACROSS THE CAPACITOR HAS REACHED OF THE SUPPLY VOLTAGE AROUND 6 IN THIS CASE /NCE YOU HAVE A NICE LOOKING PLOT FOR CHARGING AND DISCHARGING

355. PRINT OUT YOUR GRAPH SEE IG worldmagsworldmags worldmags

356. 58 Everyday Practical Electronics, December 2010 Teach-In 2011 3TART THE SIMULATION AND TEST THE CIRCUITmS OPERATION !S THE CAPACITOR CHARGES THE VOLTAGE ACROSS IT INCREASES /NCE THE VOLTAGE REACHES A CERTAIN VALUE THE TRANSISTORS lTURN ONm

357. ALLOW ING CURRENT TO ÛOW FROM THE POSITIVE OF THE BATTERY THROUGH THE BULB TO GROUND 6 AND THEREFORE LIGHTING IT 4HE LONGER IT TAKES FOR THE CAPACITOR TO CHARGE

358. THE LONGER THE DELAY WILL BE )S THE CAPACITOR BEING CHARGED OR DISCHARGED ªROM THE GRAPH

359. ESTIMATE THE TIME CONSTANT OF THE $3 CIRCUIT (INT 4AKE A LOOK AT IGØ ªª4HEª#IRCUITª7IZARDªWAY 'JH (SBQI PG DBQBDJUPS WPMUBHF QMPUUFE BHBJOTU UJNF XIJDI TIPXT ÜSTU DIBSHF BOE UIFO EJTDIBSHF BEFORE THE BULB LIGHTS 4HE CAPACITOR CHARGES THROUGH THE VARIABLE RESISTOR 62 4HEREFORE

360. BY CHANGING THE VALUE OF THE RESISTOR WE CAN CHANGE HOW FAST THE CAPACITOR CHARGES AND HENCE SET THE DELAY )TmS A BIT LIKE TURN ING A TAP TO CHANGE HOW FAST YOU ÚLL UP A BUCKET OF WATER 4RY SETTING THE VARIABLE RESISTOR SO THAT THERE IS A TWO SECOND DELAY BEFORE THE BULB LIGHTS 4HE DATA SHOWN IN 4ABLE WAS OBTAINED DURING AN EXPERIMENT ON A $3 CIRCUIT 5SE THIS DATA TO PLOT A GRAPH SHOWING HOW THE CAPACITOR VOLTAGE VARIES WITH TIME AND THEN USE THE GRAPH TO ANSWER THE FOLLOWING QUESTIONS )NVESTIGATE ª)F THE VALUE OF 3 IS -:DETERMINE THE VALUE OF $ ª(OW MUCH ENERGY IS STORED IN THE CAPACITOR AT THE START OF THE EXPERIMENT AND WHERE DOES THIS ENERGY GO 4ABLEªªª4ABLEªOFªRESULTSªFORªTHEªEXPERIMENTALª# 2ªCIRCUIT Time (s) 0 5 10 15 20 25 30 Capacitor Voltage 15.0 7.4 3.6 1.8 0.9 0.4 0.2 (V) !MAZE #APACITORS NORMALLY COME IN VERY SMALL VALUES OR EXAMPLE A P CA PACITOR HAS A VALUE OF FARADS q THATmS A PRETTY SMALL NUMBERØ )N FACT

361. A ONE FARAD CAPACITOR IS ENOR MOUS RELATIVELY SPEAKING 7HATmS THE LARGEST VALUE CAPACITOR THAT YOU CAN ÚND 4RY LOOKING AT HOW CAPACITORS ARE USED IN SOME OF THE MOST ELABORATE CAR AUDIO SYSTEMS

362. AS THEY CAN BE VERY BIGØ !NSWERSªTOª1UESTIONS 3EE PAGE

363. /HM

364. : 3EE PAGE

365. ARAD

366. 6 ! : ª 7 6 ª M# 6 6 S

367. S A BATTERY

368. B PRESET CAPA CITOR

369. C ELECTROLYTIC CAPACITOR

370. D LIGHT DEPENDENT RESISTOR ,$2

371. E VARIABLE POTENTIOMETER 6ARIABLE CAPACITOR K:

372. ‰ 2ED

373. BLACK

374. GREEN

375. BLACK

376. RED .EXT MONTHØ )N NEXT MONTHmS 4EACH )N WE SHALL BE LOOKING AT DIODES AND POWER SUPPLIES 'JH TFMFDUJPO PG DBQBDJUPST UIBU QSPWJEF TPNF FYUSFNFMZ MBSHF WBMVFT PG DBQBDJUBODF worldmagsworldmags worldmags

377. HandsOn Technology http://www.handsontec.com ISP to ICP Programming Bridge: HT-ICP200 In-Circuit-Programming (ICP) for P89LPC900 Series of 8051 Flash ȝControllers. ICP uses a serial shift protocol that requires 5 pins to program: PCL, PDA, Reset, VDD and VSS. ICP is different from ISP (In System Programming) because it is done completely by the microcontroller’s hardware and does not require a boot loader. Program whole series of P89LPC900 µController from NXP Semiconductors… USB-RS232 Interface Card: HT-MP213 A compact solution for missing ports… Thanks to a special integrated circuit from Silicon Laboratories, computer peripherals with an RS232 interface are easily connected to a USB port. This simple solution is ideal if a peripheral does not have a USB port, your notebook PC has no free RS232 port available, or none at all ! Classic P89C51 Development/Programmer Board: HT-MC-02 HT-MC-02 is an ideal platform for small to medium scale embedded systems development and quick 8051 embedded design prototyping. HT-MC-02 can be used as stand-alone 8051ȝC Flash programmer or as a development, prototyping, industry and educational platform. For professional, hobbyists…

378. 48 Everyday Practical Electronics, January 2011 Teach-In 2011 By Mike and Richard Tooley 0ARTªª$IODESªANDª0OWERª 3UPPLIES /URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEªª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS

380. ª#HECK

381. ªUILD

384. ªANDªUILDªWILLªGIVEª YOUªANªOPPORTUNITYªTOªBUILDªANDªTESTªSIMPLEªELECTRONICªCIRCUITSª)NVESTIGATEªWILLªPROVIDEªYOUªWITHªAªCHALLENGE

385. ª WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNING

386. ªANDªlNALLY

387. ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª #ONNECTIONS ARE MADE TO EACH SIDE OF THE DIODE 4HE CONNECTION TO THE Q TYPE MATERIAL IS REFERRED TO AS THE ANODE A

388. WHILE THAT TO THE O TYPE MATERIAL IS CALLED THE CATHODEª K

389. AS SHOWN IN IG ORWARDªANDªREVERSEªBIAS )F THE ANODE OF A DIODE IS MADE POSITIVE WITH RESPECT TO THE CATHODE AND PROVIDED THAT THE RELATIVELY SMALL CONDUCTION THRESHOLD VOLTAGE IS EXCEEDED THE DIODE WILL FREELY PASS CURRENT 4HIS CONDITION IS SHOWN IN IG A AND IT IS REFERRED TO AS FORWARDªBIAS #ONVERSELY

390. WHEN THE CATHODE OF A DIODE IS MADE POSITIVE WITH RESPECT TO THE ANODE

391. THE DIODE WILL CEASE TO CONDUCT 4HIS CONDITION IS SHOWN IN IG B AND IT IS REFERRED TO AS REVERSEª BIAS )N THE REVERSE BIASED CONDITION THE DIODE PASSES A NEGLIGIBLE 7($+,1 $ %52$'%$6(' ,1752'87,21 72 (/(7521,6 ,EARN INCLUDINGCONVERTINGALTERNATINGCURRENT !# TO DIRECT CURRENT $# ! DIODE IS FORMED FROM A JUNCTION OF O TYPE AND Q TYPE SEMICONDUCTOR MATERIALS 4HE RESULTING DEVICE OFFERS AN EXTREMELY LOW RESISTANCE TO CURRENT ÛOW IN ONE DIRECTION AND AN EXTREMELY HIGH RESISTANCE TO CURRENT ÛOW IN THE OTHER .OTE THAT AN lIDEALm DIODE WOULD CONDUCT PERFECTLY IN ONE DIRECTION AND NOT AT ALL IN THE OTHER DIRECTION , .ª4()3

392. OUR THIRD INSTALLMENT OF 5FBDI*O WE SHALL BE INTRO DUCING YOU TO A COMPONENT THAT ACTS RATHER LIKE A ONE WAY STREET q THE DIODE 7E SHALL BE USING #IRCUIT 7IZ ARD TO INVESTIGATE HOW DIFFERENT TYPES OF DIODE CONDUCT WHEN A VOLTAGE IS APPLIED TO THEM )NVESTIGATE PROVIDES YOU WITH AN OPPORTUNITY TO DELVE INTO THE OPERATION OF A SIMPLE $# POWER SUPPLY

393. WHILE !MAZE EXPLORES SOME EXCITING DEVELOPMENTS IN LIGHT EMIT TING DIODE ,%$ TECHNOLOGY $IODES ! DIODE IS AN ELECTRONIC COMPONENT THAT ALLOWS CURRENT TO ÛOW IN ONE DIREC TION BUT NOT IN THE OTHER )N EFFECT

394. IT ACTS AS A lONE WAY STREETm FOR CURRENT ÛOW

395. WHICHLEADSTOSOMEUSEFULAPPLICATIONS

396. 'JH %JPEF DPOTUSVDUJPO worldmags

397. Everyday Practical Electronics, January 2011 49 Teach-In 2011 AMOUNT OF CURRENT AND BEHAVES LIKE AN INSULATOR $IODEªCHARACTERISTICS 4YPICAL *7 CHARACTERISTICS FOR GERMA NIUM AND SILICON DIODES ARE SHOWN IN IG)FYOUTAKEACAREFULLOOKATTHESE GRAPHSYOUWILLSEETHATTHEAPPROXIMATE FORWARDCONDUCTIONVOLTAGEFORAGERMA NIUMDIODEIS6

398. WHILETHEVOLTAGEFOR A SILICON DIODE IS APPROXIMATELY 6 $IODEªTYPES $IODESAREOFTENDIVIDEDINTOSIGNALOR RECTIÚER TYPES ACCORDING TO THEIR PRINCI PALÚELDOFAPPLICATION3IGNALªDIODESRE QUIRECONSISTENTFORWARDCHARACTERISTICS WITHLOWFORWARDVOLTAGEDROP2ECTIlERª DIODESNEEDTOBEABLETOCOPEWITHHIGH VALUES OF REVERSE VOLTAGE AND LARGE VALUES OF FORWARD CURRENT

399. CONSISTENCY OF CHARACTERISTICS IS OF SECONDARY IMPORTANCE IN SUCH APPLICATIONS 3EMICONDUCTOR DIODES ARE ALSO AVAILABLE CONNECTED IN A FOUR DIODE BRIDGE CONÚGURATION FOR USE AS A RECTIÚER IN AN !# POWER SUPPLY IG SHOWS A SE LECTION OF VARIOUS DIODE TYPES

400. WHILE IG SHOWS THE SYMBOLS THAT ARE USED TO REPRESENT THEM IN ELECTRONIC CIRCUIT SCHEMATICS 'JH 'PSXBSE BOE SFWFSTF DPOOFD UJPOT GPS B EJPEF 'JH 5ZQJDBM WPMUBHFDVSSFOU DIBSBDUFSJTUJDT GPS UZQJDBM TJMJDPO BOE HFSNBOJVN EJPEFT /PUF UIF EJGGFSFOU TDBMFT GPS QPTJUJWF BOE OFHBUJWF WPMUBHF 'JH 7BSJPVT UZQFT PG EJPEF JODMVEJOH SFDUJÜFS TXJUDIJOH BOE MJHIUFNJUUJOH UZQFT worldmags worldmags

401. 50 Everyday Practical Electronics, January 2011 Teach-In 2011 2ECTIlERS 4HE MOST COMMON APPLICATION FOR A DIODE IS THAT OF CHANGING ALTERNATING CURRENT !# INTO DIRECT CURRENT $# IG SHOWS A SIMPLE HALF WAVE RECTI ÚER POWER SUPPLY IN WHICH THE DIODE PASSES CURRENT WHEN THE INCOMING VOLT AGE IS POSITIVE

402. BUT BLOCKS CURRENT ÛOW WHEN IT IS NEGATIVE )N ORDER TO MAIN TAIN A CONSTANT VOLTAGE AT THE OUTPUT

403. A RESERVOIR CAPACITOR IS CONNECTED ACROSS THE $# OUTPUT TERMINALS 4HIS CAPACITOR IS CHARGED ON POSITIVE HALF CYCLES AND DISCHARGES ON NEGATIVE HALF CYCLES

404. AS SHOWN IN IG !N IMPROVED

405. FULL WAVE POWER SUP PLY THAT USES A BRIDGE RECTIÚER IS SHOWN IN IG )N THIS CIRCUIT ONLY TWO OF THE FOUR DIODES OF THE BRIDGE CONDUCT AT ANY ONE TIME

406. EITHER $ AND $ OR $ AND $

407. DEPENDING ON THE POLARITY OF THE INPUT VOLTAGE 4RANSFORMERS 0OWER SUPPLIES REQUIRE SOME MEANS OF ISOLATING AND STEPPING DOWN THE !# MAINS SUPPLY BEFORE THE RECTIÚER AND RESERVOIRCAPACITOR4HISISACHIEVEDWITH THE USE OF A STEP DOWN TRANSFORMER

408. AS 'JH 4ZNCPMT VTFE UP SFQSFTFOU WBSJPVT UZQFT PG EJPEF BOE B CSJEHF SFDUJÜFS 'JH TJNQMF IBMGXBWF SFDUJÜFS 'JH 7PMUBHF XBWFGPSNT GPS UIF IBMGXBWF SFDUJÜFS 'JH *NQSPWFE GVMMXBWF CSJEHF SFDUJÜFS worldmags worldmags

409. Everyday Practical Electronics, January 2011 51 Teach-In 2011 ,IGHT EMITTINGªDIODES ,IGHT EMITTING DIODES ,%$ CAN BE USED AS GENERAL PURPOSE INDICATORS #OMPARED WITH CONVENTIONAL ÚLAMENT LAMPS

410. THEY OPERATE FROM SIGNIÚCANTLY SMALLER VOLTAGES AND CURRENTS 4HEY ARE ALSO VERY MUCH MORE RELIABLE THAN ÚLA MENT LAMPS -OST ,%$S WILL PROVIDE A REASONABLE LEVEL OF LIGHT OUTPUT WHEN A FORWARD CURRENT OF AS LITTLE AS M! TO M!

411. AT A FORWARD CONDUCTION VOLTAGE OF AROUND 6 ! TYPICAL ,%$ INDICATOR CIRCUIT IS SHOWN IN IG 4HE ÚXED RESISTOR

412. 3

413. IS USED TO SET THE FORWARD CURRENT OF THE ,%$ IN THIS CASE ABOUT M! 4HE VALUE OF THE RESISTOR MAY BE CALCULATED FROM THE FORMULA SHOWN IN IG 4HE PRIMARY AND SEC ONDARY WINDINGS OF THE TRANSFORMER ARE WOUNDONTHESAMELAMINATEDSTEELCORE 7HENCURRENTÛOWSINTHEPRIMARYWIND INGITCREATESANALTERNATINGMAGNETICÛUX THATISCOUPLEDTIGHTLYINTOTHESECONDARY WINDING 4HIS

414. IN TURN

415. INDUCES AN %- IN THE SECONDARY WINDING 4HERELATIONSHIPBETWEENTHEPRIMARY AND SECONDARY TURNS AND VOLTAGES IS AS FOLLOWS WHERE70 AND73 ARETHEPRIMARYAND SECONDARYVOLTAGES

416. WHILE/P AND/S ARE THE PRIMARY AND SECONDARY TURNS .OTE ALSOTHATTHETURNSRATIOFORATRANSFORMER IS USUALLY QUOTED AS /P /S 3O

417. FOR EX AMPLE

418. A TRANSFORMER WITH PRIMARY TURNS AND SECONDARY TURNS WOULD HAVE A TURNS RATIO OF :ENERªDIODES :ENER DIODES ARE SILICON DIODES THAT

419. UNLIKENORMALDIODES

420. EXHIBITANABRUPT REVERSEBREAKDOWNATRELATIVELYLOWVOLT AGES FOR EXAMPLE

421. 6

422. 6 OR 6 4HE CIRCUIT SYMBOL FOR A :ENER DIODE WAS SHOWN EARLIER IN IG

423. WHILE A TYPICAL:ENERDIODECHARACTERISTICCURVE IS SHOWN IN IG 7HEN A :ENER DIODE IS UNDERGOING REVERSE BREAKDOWN

424. AND PROVIDED ITS MAXIMUM RATINGS ARE NOT EXCEEDED

425. THE VOLTAGE APPEARING ACROSS IT WILL REMAIN SUBSTANTIALLY CONSTANT REGARDLESS OF THE CURRENT ÛOWING 4HIS PROPERTY MAKES A :ENER DIODE IDEAL FOR USE AS A VOLTAGE REGULATOR

426. AS SHOWN IN IG 'JH UZQJDBM TFU PG ;FOFS EJPEF DIBSBDUFSJTUJDT 'JH TJNQMF ;FOFS EJPEF WPMUBHF SFHVMBUPS 'JH UZQJDBM -% JOEJDBUPS 'JH USBOTGPSNFS WHERE 7G IS THE FORWARD VOLTAGE DROP FOR THE ,%$ TYPICALLY AROUND 6

427. 7 IS THE SUPPLY VOLTAGE AND * IS THE FORWARD CURRENT 0LEASE NOTEØ 4HE LARGE VALUE RESERVOIR CAPACITOR IN A POWER SUPPLY CAN OFTEN REMAIN IN A PARTIALLY CHARGED STATE LONG AFTER THE SUPPLY HAS BEEN SWITCHED OFF OR DISCON NECTED ECAUSE OF THIS

428. IT IS IMPORTANT TO EXERCISE GREAT CARE WHEN WORKING ON POWER SUPPLY CIRCUITSØ (a) Transformer symbol, voltages and turns (b) A typical transformer 3 3 6 6 9 1 9 1 I9 9 5 , worldmags worldmags

429. 52 Everyday Practical Electronics, January 2011 Teach-In 2011 3KETCH THE CIRCUIT SYMBOL FOR A DIODE AND LABEL THE ANODE AND CATHODE CONNECTIONS 7HAT IS A THE FORWARD RESISTANCE AND B THE REVERSE RESISTANCE OF AN lIDEALm DIODE 7HICHOFTHEDIODESSHOWNINIGISCONDUCTING #HECKªnª(OWªDOªYOUªTHINKª YOUªAREªDOING 3TATE THE FORWARD CONDUCTION VOLTAGE FOR A A GERMA NIUM DIODE AND B A SILICON DIODE %XPLAIN BRIEÛY HOW A RECTIÚER OPERATES %XPLAIN WHY A RESERVOIR CAPACITOR IS NEEDED IN A POWER SUPPLY )DENTIFYEACHOFTHEDIODESYMBOLSSHOWNINIG 'JH 4FF RVFTUJPO ! TRANSFORMER HAS PRIMARY TURNS AND SEC ONDARY TURNS $ETERMINE THE SECONDARY OUTPUT VOLTAGE IF THE PRIMARY IS SUPPLIED FROM A 6 !# MAINS SUPPLY 'JH 4FF RVFTUJPO ,. 4()3 MONTHmS lUILDm WE ARE GOING TO TRY OUT SOME OF THE DIODE THEORY THAT WE DISCUSSED EARLIER 4O START WITH

430. WEmLL CARRY OUT SOME SIMPLE EXPERIMENTS WITH ORDINARY SILICON DIODES TO SEE HOW THEY REALLY WORK )N l,EARNm WE SAW HOW A DIODE ACTS LIKE A ONE WAY VALVE (OWEVER

431. BY USING A REALLY HIGH REVERSE VOLTAGE WE CAN MAKE A DIODE BREAK DOWN AND LET THROUGH CURRENT lBACK WARDSm 7E ALSO KNOW THAT IT TAKES A LITTLE VOLTAGE TO lOPEN UPm A DIODE AND MAKE IT START LETTING CURRENT ÛOW THROUGH IT 3O LETmS TRY THIS OUTØ $IODEªTESTªCIRCUIT %NTER THE CIRCUIT SHOWN IN IG 9OUmLL ÚND THE DIODE IN THE l$ISCRETE SEMICONDUC TORSm FOLDER

432. THE INPUT VOLTAGE IN l0OWER 3UP PLIESmANDTHEMETERSINl6IRTUAL)NSTRUMENTSm Y DEFAULT #IRCUIT 7IZARD WILL GIVE YOU AN 'JH 5FTUJOH B TJMJDPO EJPEF VTJOH GPSXBSE CJBT 'JH 4FMFDUJOH UIF NPEFM GPS B EJPEF worldmags worldmags

433. Everyday Practical Electronics, January 2011 53 Teach-In 2011 ªªUILDªnª4HEª#IRCUITª7IZARDªWAY 'JH YDFM HSBQI PG SFTVMUT GPS / JO GPSXBSE CJBT lIDEALm DIODE !S WE WANT TO SEE HOW A REAL DIODE MIGHT WORK YOU NEED TO SELECT A MODEL 4O DO THIS

434. DOUBLE CLICK THE DIODE SYMBOL AND SELECT l.m FROM THE l-ODELm DROP DOWN LIST SEE IG 4HE . IS A STANDARD SILICON RECTIÚER DIODE AND IS VERY COM MONLY USED 4EST 7HAT WE HAVE HERE IS A REALLY SIMPLE CIRCUIT q PROBABLY NOT ONE THAT YOUmD USE IN REAL LIFE (OWEVER

435. IT LETS US SEE HOW MUCH CURRENT THE DIODE PASSES DEPENDING ON WHAT VOLTAGE WE PUT ACROSS IT 4O CARRY OUT OUR TEST

436. WHAT WEmLL DO IS SLOWLY INCREASE THE VOLTAGE ACROSS THE DIODE AND SEE WHAT CURRENT ÛOWS THROUGH IT 4HIS WILL TELL US IF THE DIODE IS CONDUCTING IRST

437. TRY STARTING THE SIMULATION BY HITTING THE PLAY BUTTON ON THE TOP BAR 5SE THE SLIDER TO VARY THE INPUT VOLT AGE AND WATCH THE EFFECT 9OUmLL ONLY NEED TO INCREASE THE VOLTAGE TO ABOUT 6

438. AT WHICH POINT THE DIODE SHOULD BE CONDUCTING NICELY AND YOU SHOULD SEE A LARGE VALUE FOR THE CURRENT 9OU MIGHT ÚND IT EASIER TO SET THE LIMIT FOR THE INPUT VOLTAGE TO 6 ITmS SET 'JH YDFM HSBQI GPS / JO SFWFSTF CJBT AT 6 BY DEFAULT q THIS WILL ALSO HELP YOU WITH THE NEXT BITØ 9OU CAN DO THIS BY DOUBLE CLICKING THE COMPONENT AND CHANGING THE 6 TO 6 (OPEFULLY

439. YOU SHOULD NOTICE THAT IT DOESNmT SIMPLY START LETTING A LARGE CUR RENT PASS IMMEDIATELY q IT TAKES A LITTLE VOLTAGE ACROSS IT TO REALLY lOPEN IT UPm ) ALWAYS LIKE TO THINK OF A DIODE LIKE A SPRUNG ONE WAY GATE ITmS EASY TO GET THROUGH ITINTHERIGHTDIRECTION

440. BUTYOU NEED TO PUT A LITTLE PRESSURE AGAINST IT IN ORDER TO GET THROUGH 4AKINGªREADINGS .OW LETmS GET A LITTLE MORE SCIENTIÚC ABOUTTHINGSANDTAKESOMEREADINGS7E CAN THEN DRAW UP A GRAPH OF OUR RESULTS TO SEE WHATmS GOING ON 3TARTING FROM 6 AND STEPPING UP IN 6 M6 STEPS

441. INCREASETHEVOLTAGE AND RECORD THE CURRENT ÛOWING THROUGH THE DIODE /NCE YOUmVE GOT A FULL SET OF RESULTS YOU CAN USE THEM TO DRAW A GRAPH 4AKE CARE TO MAKE SURE THAT ALL OF YOUR CURRENT READINGS ARE IN THE SAME UNITS WHEN YOU PLOT YOUR GRAPHØ !N EXAMPLE USING -ICROSOFT %XCEL IS SHOW IN IG !S YOU HAVE FOUND

442. ONCE WE GET TO AROUND6THEDIODE STARTS TO LET CURRENT THROUGH

443. AND THIS IS WHAT WEmD EXPECT FOR A SILICON DIODE 3O FAR WEmVE BEEN USING THE DIODE lTHE RIGHT WAY ROUNDm IN WHAT WE CALL FORWARDªBIAS .OW WEmLL SEE WHAT HAPPENS WHEN WE TURNTHEDIODEAROUND SO THATmS ITmS IN REVERSEª BIAS OR lBACKWARDSm !LTER YOUR CIRCUIT TO THAT SHOWN IN IG.OTICETHATASWELLASTHEDIODE ORIENTATION CHANGING

444. THE TOP LIMIT ON THE INPUT VOLTAGE HAS BEEN INCREASED TO 6 3TART THE SIMULATION AND TRY EXPERIMENTING WITH THE INPUT VOLTAGE 9OU SHOULD ÚND THAT ITmS REALLY HARD TOGETADIODETOCONDUCTINREVERSEBIASØ 'OING BACK TO THE IDEA OF A DIODE AS A ONE WAY GATE IF YOU REALLY WANTED TO GETTHROUGHITTHEWRONGWAYYOUWOULD BE ABLE TO DO IT

445. BUT YOUmD HAVE TO WORK REALLY HARD TO FORCE IT OPEN 4HEREFORE

446. ITmS NOT STRICTLY TRUE THAT A STANDARDDIODEONLYLETSCURRENTTHROUGH IN ONE DIRECTIONØ (OWEVER

447. IN PRACTICE

448. IF YOU WERE USING A DIODE IN A LOW VOLT AGE CIRCUIT IT IS UNLIKELY THAT A REVERSE VOLTAGE WOULD EVER BE HIGH ENOUGH TO BREAK IT DOWN 2ECORDVALUESFORTHEVOLTAGEANDCUR RENT GOING UP IN STEPS OF 6 AND GRAPH YOUR RESULTS 4IP YOUmLL ALSO NEED TO GO TO 6 TO GET YOUR ÚNAL READINGØ 9OU SHOULD OBTAIN SOMETHING THAT LOOKS LIKE THE GRAPH SHOWN IN IG )RU RXUFRS RI LUFXLW:L]DUG ²VHH '520SDJHV 'JH $JSDVJU GPS EJPEF UFTUJOH JO SFWFSTF CJBT worldmags worldmags

449. 54 Everyday Practical Electronics, January 2011 Teach-In 2011 .OW REPEAT THIS FOR SOME MORE :ENER VOLTAGE VALUES (EREmS OUR RESULTS FOR THREE :ENER DIODES 6 6

450. 6 6 AND 6 6 )F YOU CARRIED OUT YOUR EXPERIMENTS ACCURATELY

451. YOU SHOULD BE ABLE TO PRO DUCE A GRAPH SIMILAR TO THAT SHOWN IN IG .OTICE THAT THE CURRENT RAPIDLY INCREASES THROUGH THE DIODE ONCE IT REACHES THE :ENER VOLTAGE OF THE DIODE 4HIS CAN BE EXTREMELY USEFUL IN ELECTRONIC CIRCUITS 7E OFTEN USE :ENER DIODES TO GIVE US EXACT REFERENCE VOLTAGES AND TO REGULATE VOLTAGES DOWN TO A SPECIÚC VALUE 3EMICONDUCTORMANUFACTURERSOFTEN PRODUCE A GRAPH OF THE CHARACTERISTICS OF THEIR DIODES SIMILAR TO THOSE THAT YOUmVE CREATED (OWEVER

452. THEY USU ALLY RECORD THE VOLTAGES AND CURRENTS IN REVERSE BIAS AS NEGATIVE

453. AND SHOW THEM BOTH ON ONE GRAPH 4RY THIS WITH YOUR RESULTS AND SEE IF YOU CAN PRODUCEAMANUFACTURER LIKEGRAPHFOR THE.4AKEALOOKATOURS

454. WHICH WEmVE SHOWN IN IG 3O WEmVE SEEN HOW A STANDARD DI ODE LETS CURRENT THROUGH IN A FORWARD DIRECTION ONCE THERE IS A SMALL VOLTAGE ACROSS IT

455. BUT NORMALLY BLOCKS CURRENT IN A REVERSE DIRECTION UNLESS WE APPLY A REALLY LARGE VOLTAGE :ENERªDIODES $IODES ARE A REALLY USEFUL DEVICE TO HELP US CONTROL WHERE CURRENT ÛOWS IN A CIRCUIT AND ARE ESSENTIAL WHEN IT COMES TO CONVERTING ALTERNATING CUR RENT !# TODIRECTCURRENT $# WECALL THIS VOLTAGE RECTIlCATION (OWEVER

456. AS YOU MET IN THE l,EARNm SECTION

457. THERE IS ALSO ANOTHER TYPE OF DIODE THAT HAS A SPECIAL

458. AND RATHER USEFUL FEATURE WHEN ITCOMESTOREVERSEBIAS4HESEARECALLED :ENER DIODES ASICALLY

459. WHEN WE MANUFACTURE A :ENER DIODE WE CAN ENGINEER IT SO THAT WE KNOW AT EXACTLY WHAT VOLTAGE IT WILL BREAKDOWNINREVERSEBIASANDCONDUCT 9OU CAN PURCHASE A FULL RANGE OF :ENER DIODESWITHDIFFERENTSPECIÚEDVOLTAGES 3O LETmS TRY OUR PREVIOUS DIODE EX PERIMENTS

460. BUT WITH SOME :ENER DIODES INSTEADOFORDINARYSILICONDIODES!LTER YOUR REVERSE BIAS DIODE CIRCUIT SHOWN IN IG BY CHANGING THE DIODE TO A :ENER DIODE q SEE IG 7E NEED TO SPECIFY THE :ENER VOLTAGE OF THE DIODE AND WE DO THIS IN THE SAME WAY AS WE SELECTED THE DIODE MODEL PREVIOUSLY

461. BYDOUBLECLICKINGTHE:ENER DIODE AND SELECTING A VOLTAGE FROM THE l-ODELm DROP DOWN LIST SEE IG 4O START WITH

462. SELECT 6 6 THEN SLOWLY INCREASE THE VOLTAGE ACROSS THE DIODETAKINGREADINGSEVERY6UNTIL THE CURRENT REACHES AROUND M! 'JH YDFM HSBQI TIPXJOH / DIBSBDUFSJTUJDT JO CPUI GPSXBSE BOE SFWFSTF CJBT ªªªªªªª4HEª#IRCUITª7IZARDªWAY For more information, links and other resources please check out ourTeach-In website at: www.tooley.co.uk/ teach-in 'JH ;FOFS EJPEF UFTU DJSDVJU 'JH 4FMFDUJOH UIF ;FOFS EJPEF NPEFM 'JH $IBSBDUFSJTUJDT GPS UISFF EJGGFSFOU ;FOFS EJPEFT worldmags worldmags

463. Everyday Practical Electronics, January 2011 55 Teach-In 2011 !S YOUmVE SEEN

464. ,%$S ARE A TYPE OF DIODE THAT EMITS LIGHT WHEN THE DEVICE IS FORWARD BIASED AND PASSING CURRENT ,%$SHAVEBEENAROUNDINVARIOUSFORMS FOR QUITE A LONG TIME AND SO YOU WILL ALREADY BE FAMILIAR WITH THEM AND HOW THEY ARE USED ,%$S OFFER SOME NOTABLE ADVANTAGES WHEN COMPARED WITH ÚLA MENT LAMPS AND ÛUORESCENT DISPLAYS p 4HEY ARE EXTREMELY RELIABLE AND THEY CAN OPERATE FOR MANY TENS OR EVEN HUNDREDS OF THOUSANDS OF HOURS IF USED AT THEIR RATED CURRENT p 4HEY ARE IMPERVIOUS TO HEAT

465. COLD

466. SHOCK AND VIBRATION p4HEYAREVERYEFÚCIENTANDPRODUCE VERY LITTLE HEAT

467. SO RUN COOL p 4HEY OPERATE FROM LOW VOLTAGE AND CURRENT

468. AND CAN BE EASILY INTERFACED TO ELECTRONIC CIRCUITS p 4HEY ARE RUGGED BECAUSE NO BREAK ABLE GLASS IS USED IN THEIR CONSTRUCTION !NSWERSªTOª1UESTIONS 3EE IG A A ZERO B INÚNITE $ AND $ A 6 B 6 3EE PAGE 3EE PAGE A PHOTODIODE B :ENER DIODE C LIGHT EMITTINGDIODE ,%$ 6 )NVESTIGATE !MAZE IGSHOWSTHECIRCUITOFAPOWER SUPPLY3TUDYTHECIRCUITCAREFULLY

469. LOOK BACK AT WHAT WE DID IN 0ART AND THEN ANSWEREACHOFTHEFOLLOWINGQUESTIONS 7HAT TYPE OF RECTIÚER IS USED IN THE POWER SUPPLY 7HAT IS THE TURNS RATIO OF THE TRANSFORMER 7HAT !# VOLTAGE WILL APPEAR AT THE INPUT OF THE BRIDGE RECTIÚER )F THE ,%$ HAS A FORWARD VOLTAGE OF 6

470. WHAT CURRENT IS SUPPLIED TO IT 7HAT POWER WILL BE DISSIPATED IN THE :ENER DIODE 'JH 4FF *OWFTUJHBUF 'OINGªORGANIC 2ECENT ADVANCES IN SEMICONDUCTOR TECHNOLOGY HAVE SEEN THE INTRODUCTION OF WHITE lHIGH BRIGHTNESSm ,%$S THAT CAN BE USED IN GROUPS OR ARRAYS TO REPLACE LAMPSUSEDINDOMESTICLIGHTINGAPPLICA TIONS$EVELOPEDBY+ODAKINTHES

471. ORGANIC LIGHT EMITTING DIODES /,%$ SEEM POISED TO OUST THE ,#$ DISPLAY JUST AS ,#$ TECHNOLOGY HAS ECLIPSED THE #24 /,%$ PANELS ARE THINNER

472. CRISPER

473. BRIGHTER AND MORE ENERGY EFÚCIENT THAN THEIR ,%$ COUNTERPARTS !N /,%$ PANEL CONSISTS OF A LAYER OF ORGANIC

474. LIGHT EMITTING MATERIAL SAND WICHED BETWEEN TWO CONDUCTORS AN ANODE AND A CATHODE 4HE RESULTING DEVICE IS ABOUT TIMES THINNER THAN A HUMAN HAIR AND IT EMITS LIGHT WHEN AN ELECTRIC CURRENT IS PASSED THROUGH IT 4HEREmS NO NEED FOR A BACKLIGHT BECAUSE THE ORGANIC MATERIAL EMITS ITS OWN LIGHT WHEN CHARGED 4HE ABSENCE OF A BACKLIGHT MEANS THAT /,%$ DISPLAYS CAN BE EXTREMELY THIN OR EXAMPLE

475. THE 3ONY 8%, IS ONLY MM THICK AND 3ONYmS PROTOTYPE INCH /,%$ 46 USES A PANEL WHICH HAS A THICKNESS OF AS LITTLE AS MMØ )N THE SAME WAY THAT INKS ARE SPRAYED ONTO PAPER DURING PRINTING

476. /,%$S CAN BE SPRAYED ONTO SUBSTRATES USING INKJET TECHNOLOGY 4HIS REDUCES THE COST OF MANUFACTURING AND ALLOWS DISPLAYS TO BE PRINTED ONTO VERY LARGE ÚLMS THAT CAN BE USED IN GIANT SCREENS AND ELECTRONIC BILLBOARDS 3O

477. IF YOU FANCY A INCH 46 DISPLAY THAT ROLLS UP FOR STORAGE

478. OR IF YOU THINK IT MIGHT BE USEFUL TO HAVE A DISPLAY BUILT INTO YOUR CLOTHING

479. YOU MIGHT NOT HAVE TO WAIT TOO LONGØ .EXT MONTHØ )N PART

480. NEXT MONTHmS 4EACH )N

481. WE WILL LOOK AT TRANSISTORS 'JH O FBSMZ QSPUPUZQF 0-% EJTQMBZ QIPUP DPVSUFTZ PG . )BSSJT worldmags worldmags

482. 46 Everyday Practical Electronics, February 2011 Teach-In 2011 By Mike and Richard Tooley 0ARTªª4RANSISTORS /URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS

483. ªASªWELLªASªELECTRONICSª UNITSªOFªTHEªNEWª$IPLOMAªINª%NGINEERINGª ALSOªATª,EVELª ª4HEªSERIESªWILLªALSOªPROVIDEªTHEªMOREªEXPERIENCEDª READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUP ªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª %ACHªPARTªOFªOURª4EACH )NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARN

484. ª#HECK

485. ªUILD

489. ªANDªlNALLY

490. ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª EXTREMELY SMALL AND THEY ARE PRO DUCED IN A SINGLE SLICE OF SILICON BY DIFFUSING IMPURITIES THROUGH A PHOTOGRAPHICALLY REDUCED MASK 3IMPLIFIED REPRESENTATIONS OF /1/ AND 1/1 TRANSISTORS ARE SHOWN

491. TOGETHER WITH THEIR SYM BOLS

492. IN IG

493. 4HE CONNECTIONS TO THE SEMICONDUCTOR MATERIAL ARE LABELLED COLLECTORª C

494. BASE B AND EMITTERª E !N IMPORTANT POINT TO NOTE IS THAT BOTH TYPES OF TRANSISTOR CONSIST OF TWO DIODE 1 / JUNCTIONS BACK TO BACK (OWEVER

495. ITmS IMPORTANT TO REALISE THAT THE MIDDLE LAYER THE 1 TYPE BASE REGION IN AN /1/ TRANSIS TOR OR THE / TYPE BASE REGION IN THE 1/1 TRANSISTOR IS MADE EXTREMELY NARROW

496. AND THIS ALLOWS CHARGE 7($+,1 $ %52$'%$6(' ,1752'87,21 72 (/(7521,6 ,EARN 4RANSISTORS 4HERE ARE SEVERAL DIFFERENT TYPES OF TRANSISTOR

497. BUT FOR CONVENIENCE THEY ARE OFTEN DIVIDED INTO TWO MAIN CATEGORIES BIPOLARªJUNCTIONªTRANSIS TORSª *4 AND lELD EFFECTªTRANSISTORSª %4 !LTHOUGH THE PRINCIPLE ON WHICH THEY OPERATE IS DIFFERENT

498. THEY ARE OFTEN USED IN SIMILAR APPLICA TIONS

499. AND BECAUSE OF THIS WE WILL FOCUS OUR ATTENTION ON *4 RATHER THAN %4 DEVICES ! SELECTION OF DIFFERENT TYPES OF TRANSISTOR INCLUD ING *4 AND %4 DEVICES IS SHOWN IN IG IPOLAR JUNCTION TRANSISTORS ARE MADE OF /1/ OR 1/1 JUNCTIONS OF SILICON 3I 4HE JUNCTIONS ARE , . PART FOUR OF 5FBDI*O

500. WE WILL INTRODUCE YOU TO A COM PONENT THAT CAN ACT AS BOTH AN AMPLIÚER AND A SWITCH /RIGINALLY CALLED A lTRANSFER RESISTORm

501. THE UBIQ UITOUS TRANSISTOR IS FOUND IN ALMOST EVERY ELECTRONIC CIRCUIT

502. EITHER AS A DISCRETE COMPONENT

503. OR AS PART OF AN INTEGRATED CIRCUIT 7E WILL USE #IRCUIT 7IZARD TO IN VESTIGATE THE OPERATION OF A TRANSIS TOR AS A DEVICE FOR AMPLIFYING AND SWITCHING CURRENT 9OU WILL ALSO BE ABLE TO CONSTRUCT AND TEST A SIMPLE LIGHT ÛASHER THAT USES LIGHT EMITTING DIODES ,%$ INALLY

504. IN !MAZE WE TAKE THIS ONE STEP FURTHER BY SHOW ING YOU HOW TO DESIGN A PRINTED CIRCUIT BOARD 0# LAYOUT FOR THE ,%$ ÛASHERØ worldmagsworldmags worldmags

505. Everyday Practical Electronics, February 2011 47 Teach-In 2011 CARRIERS TO PASS ACROSS IT RATHER THAN ENTER OR EXIT AT THE BASE 4HUS

506. THE MAIN CURRENT ÛOW IN A TRANSISTOR IS FROM COLLECTOR TO EMITTER IN THE CASE OF A /1/ TRANSISTOR

507. OR FROM EMITTER TO COLLECTOR IN THE CASE OF A 1/1 TRANSISTOR

508. AS SHOWN IN IG AND IG IG AND IG

509. RESPECTIVELY

510. SHOW THE NORMAL VOLTAGES APPLIED TO /1/ AND 1/1 TRANSISTORS AND THE CURRENT ÛOW WITHIN THE DEVICE )T IS IMPORTANT TO NOTE FROM THIS THAT THE BASE EMITTER JUNCTION IS FORWARD BIASED

511. AND THE COLLECTOR BASE JUNC TION IS REVERSE BIASED ECAUSE THE BASE REGION IS MADE VERY NARROW

512. CHARGE CARRIERS ARE SWEPT ACROSS IT AND ONLY A RELATIVELY SMALL NUMBER APPEAR AT THE BASE 4O PUT THIS INTO CONTEXT

513. THE CUR RENT ÛOWING IN THE EMITTER CIRCUIT IS TYPICALLY TIMES GREATER THAN THAT ÛOWING IN THE BASE 4HE EQUATION THAT RELATES CURRENT ÛOW IN THE COLLECTOR

514. BASE

515. AND EMIT TER CURRENTS IS IE = IB + IC WHERE *% IS THE EMITTER CURRENT

516. * IS THE BASE CURRENT

517. AND *# IS THE COLLECTOR CURRENT ALL EXPRESSED IN THE SAME UNITS 'JH TFMFDUJPO PG EJGGFSFOU #+5 BOE '5 EFWJDFT 'JH 'MPX PG DVSSFOU JO BO .0. USBOTJTUPS 'JH 'MPX PG DVSSFOU JO B 0.0 USBOTJTUPS 'JH CFMPX 4ZNCPMT TJNQMJÜFE NPEFMT BOE DPOTUSVDUJPO PG .0. BOE 0.0 CJQPMBS KVODUJPO USBOTJTUPST worldmagsworldmags worldmags

518. 48 Everyday Practical Electronics, February 2011 Teach-In 2011 4HE VALUE OF *% CAN BE CALCULATED BY RE ARRANGING THE EQUATION *% * *# TO MAKE *# THE SUBJECT

519. AS FOLLOWS *# *% q *# q M! .OTE THAT ! IS THE SAME AS M! *4ªCIRCUITªCONlGURATIONS 2EGARDLESS OF WHETHER A *4 IS AN /1/ OR 1/1 TYPE

520. THREE BASIC CIRCUIT CONÚGURATIONS ARE USED

521. AND ALL TRANSISTOR BNQMJÜFS STAGES ARE BASED ON ONE OF THESE 4HE THREE CIRCUITS ARE BASED ON WHICH ONE OF THE THREE TRANSISTOR CONNECTIONS IS MADE COMMON TO BOTH THE INPUT AND THE OUTPUT )N THE CASE OF *4S

522. THE CONÚGURATIONS ARE KNOWN AS COM MONªEMITTER

523. COMMONªCOLLECTOR OR EMITTERªFOLLOWER AND COMMONªBASE SEE IG .OTE THAT WE HAVE INCLUDED A RESIS TOR KNOWN AS A LOAD

524. MARKED 3- IN IG WHICH CONVERTS THE OUTPUT 0LEASE NOTEØ 4HE DIRECTION OF CONVENTIONAL CUR RENT ÛOW IS FROM COLLECTOR TO EMITTER IN THE CASE OF AN /1/ TRANSISTOR

525. AND EMITTER TO COLLECTOR IN THE CASE OF A 1/1 TRANSISTOR )N BOTH CASES

526. THE AMOUNT OF CURRENT ÛOWING FROM COLLECTOR TO EMITTER IS DETERMINED BY THE AMOUNT OF CURRENT ÛOWING INTO THE BASE 0LEASE NOTEØ 4HERE ARE MANY DIFFERENT TYPES OF TRANSISTOR )N THIS INSTALMENT OF 4EACH )NWEAREJUSTLOOKINGATONEOFTHEMOST COMMON TYPES

527. THE BIPOLAR JUNCTION TRANSISTOR *4 IGSHOWSSYMBOLS FOR SOME OF THE OTHER LESS COMMON TYPES THAT YOU MIGHT COME ACROSS %XAMPLEª ! TRANSISTOR OPERATES WITH A COLLEC TOR CURRENT OF M! AND AN EMITTER CURRENT OF M! $ETERMINE THE VALUE OF BASE CURRENT 4HE VALUE OF *% CAN BE CALCULATED BY RE ARRANGING THE EQUATION *% * *# TO MAKE * THE SUBJECT

528. AS FOLLOWS * *% q *# (ENCE * q M! %XAMPLEª ! TRANSISTOR OPERATES WITH *% M! AND * ! $ETERMINE THE VALUE OF *# 'JH 4ZNCPMT VTFE GPS PUIFS UZQFT PG USBOTJTUPS 3DUDPHWHU RPPRQ HPLWWHU RPPRQ FROOHFWRU RPPRQ EDVH 9ROWDJH JDLQ 0HGLXPKLJK

529. 8QLW

530. +LJK

531. XUUHQW JDLQ +LJK

532. +LJK

533. 8QLW

534. 3RZHU JDLQ 9HU KLJK

535. +LJK

536. +LJK

537. ,QSXW UHVLVWDQFH 0HGLXP Nȍ

538. +LJK Nȍ

539. /RZ ȍ

540. 2XWSXW UHVLVWDQFH 0HGLXPKLJK Nȍ

541. /RZ ȍ

542. +LJK Nȍ

543. 3KDVH VKLIW ƒ ƒ ƒ 7SLFDO DSSOLFDWLRQV *HQHUDO SXUSRVH DPSOLILHU VWDJHV ,QSXW DQG RXWSXW VWDJHV ZKHUH QR YROWDJH JDLQ LV QHHGHG

544. 5DGLR IUHTXHQF DPSOLILHUV 4ABLEªª#HARACTERISTICSªOFªTHEªTHREEª*4ªCIRCUITªCONlGURATIONS 'JH #JQPMBS KVODUJPO USBOTJTUPS #+5 DJSDVJU DPOÜHVSBUJPOT Parameter Common emitter Common collector Common base worldmagsworldmags worldmags

545. Everyday Practical Electronics, February 2011 49 Teach-In 2011 5SING THE RELATIONSHIP #URRENT GAIN GIVES #URRENT GAIN %XAMPLEª ! *4 HAS A COMMON EMITTER CURRENTGAINOF)FTHETRANSISTOROP ERATESWITHACOLLECTORCURRENTOFM!

546. DETERMINE THE VALUE OF BASE CURRENT 2EARRANGING THE CURRENT GAIN FOR MULA TO MAKE *# THE SUBJECT GIVES CURRENT TAKEN FROM THE COLLECTOR OR EMITTER INTO A CORRESPONDING VOLT AGE WHICH APPEARS AT THE OUTPUT 4HE THREE CIRCUIT CONFIGURATIONS EXHIBIT QUITE DIFFERENT PERFORMANCE CHARACTERISTICS

547. AS LISTED IN 4ABLE 4YPICAL VALUES HAVE BEEN INCLUDED IN BRACKETS #URRENTªGAIN *4S ARE PRIMARILY CURRENT AM PLIFYING DEVICES

548. IN WHICH A SMALL CURRENT AT THE BASE B INÛUENCES A MUCH LARGER CURRENT AT THE COLLECTOR C 4HERE IS A DIRECT RELATIONSHIP BETWEEN THESE TWO CURRENTS OR EX AMPLE

549. DOUBLING THE CURRENT APPLIED TO THE BASE WILL CAUSE THE COLLECTOR CURRENT TO DOUBLE

550. AND SO ON )N THE CASE OF THE COMMON EMITTER MODE WHERE THE INPUT IS CONNECTED TO THE BASE AND THE OUTPUT IS TAKEN FROM THE COLLECTOR

551. THE CURRENT GAIN IS THE RATIO OF COLLECTOR CURRENT TO BASE CURRENT (ENCE #URRENT GAIN 4O UNDERSTAND THIS IMPORTANT EFFECT

552. TAKE A LOOK AT IG 4HIS SHOWS A TRANSISTOR WITH A CURRENT GAIN OF OPERATING IN COMMON EMITTER CONÚGURATION WITH THREE DIF FERENT VALUES OF BASE CURRENT APPLIED )N IG A THERE IS NO BASE CUR RENT

553. SO THEREmS ALSO NO COLLECTOR CUR RENT )N IG B

554. THE BASE CURRENT HAS INCREASED TO M! ! AND THIS HAS CAUSED THE COLLECTOR CURRENT TO INCREASE FROM ZERO TO M! ! FURTHER INCREASE IN BASE CURRENT FROM M! TO M! ! CAUSES THE COLLECTOR CURRENT TO INCREASE BY A FURTHER M! TO M! 7E COULD NOW PLOT A GRAPH OF THESE RESULTS SO THAT WE CAN PREDICT THE COLLECTOR CURRENT FOR ANY GIVEN VALUE OF BASE CURRENT .OT SURPRIS INGLY

555. THIS GRAPH WHICH IS KNOWN AS A TRANSFERªCHARACTERISTIC

556. BECAUSE IT SHOWS INPUT PLOTTED AGAINST OUTPUT TAKES THE FORM OF A STRAIGHT LINE

557. AS SHOWN IN IG %XAMPLEª ! TRANSISTOR OPERATES WITH A COL LECTOR CURRENT OF M! AND A BASE CURRENT OF ! 7HAT IS THE COMMON EMITTER CURRENT GAIN OF THE TRANSISTOR 'JH UPQ MFGU $VSSFOU ÝPX JO B TJNQMF #+5 DPNNPO FNJUUFS BNQMJÜFS 'JH CFMPX 0VUQVU DVSSFOU QMPUUFE BHBJOTU JOQVU DVSSFOU GPS UIF #+5 JO 'JH 'JH CFMPXMFGU TJNQMF DPNNPOFNJUUFS BNQMJÜFS DJSDVJU % , , % FXUUHQW JDLQ , , FROM WHICH IAS 7HEN WE USE A *4 TO AMPLIFY SIGNALS

558. SUCH AS SPEECH OR MUSIC

559. WE NEED TO ENSURE THAT THE TRANSIS TOR IS ALWAYS CONDUCTING AN AMOUNT OF STANDING COLLECTOR CURRENT 7E ACHIEVE THIS BY APPLYING A BIAS # % , , # %, % P$ RU ȝ$

560. ,%, P$ RU ȝ$

561. worldmags worldmags

562. 50 Everyday Practical Electronics, February 2011 Teach-In 2011 CURRENT TO THE BASE OF THE TRANSIS TOR 4HIS MEANS THAT A STATIC VALUE OF COLLECTOR CURRENT WILL ÛOW EVEN WHEN THERE IS NO SIGNAL PRESENT 4HE COLLECTOR CURRENT CAN THEN INCREASE ABOVE OR DECREASE BELOW THIS STAND ING VALUE OF CURRENT

563. DEPENDING UPON THE POLARITY OF THE INPUT SIGNAL )F THIS SOUNDS A LITTLE COMPLICATED TAKEALOOKATTHESIMPLECOMMONEMIT TER AMPLIÚER CIRCUIT SHOWN IN IG 4HE SIGNAL WHICH IS !# IS COU PLED INTO THE AMPLIÚER VIA CAPACITOR # AND OUT OF THE AMPLIÚER VIA # 4HESE TWO CAPACITORS HELP TO ISOLATE THE TRANSISTOR STAGE SO THAT THE $# VOLTAGESANDCURRENTSINSIDEITAREUN AFFECTED BY WHATEVER IS CONNECTED TO THE INPUT AND OUTPUT TERMINALS 4HE BIASCURRENT WHICHÛOWSALLTHETIME IS JOINED BY THE SIGNAL CURRENT BEFORE ENTERING THE BASE OF THE TRANSISTOR )N A SIMILAR MANNER

564. THE TRAN SISTORmS COLLECTOR CURRENT HAS TWO COMPONENTS

565. A $# VALUE RESULTING FROM THE STEADY BIAS CURRENT AND AN !# CURRENT SUPERIMPOSED ON IT RESULTING FROM THE AMPLIÚED SIGNAL CURRENT 4HESE CURRENTS JOIN TOGETHER AND ÛOW THROUGH THE COLLECTORªLOAD 2 ACROSS WHICH THE OUTPUT VOLTAGE IS DEVELOPED .OTE THAT THE OUTPUT VOLTAGE HAS THE SAME SHAPE AS THE INPUT VOLTAGE

566. BUT IS INVERTED OR TURNED THROUGH ˆ INALLY

567. THE VOLTAGE DROP BETWEEN THE COLLECTOR AND EMITTER CAN BE CAL CULATED FROM .OW LETmS SEE IF WE CAN CALCULATE THE BASE AND COLLECTOR VOLTAGES AND CURRENTS WHEN NO SIGNAL IS PRESENTØ IG SHOWS THE AMPLIÚER CIRCUIT REDRAWN

568. OMITTING THE INPUT AND OUT PUT COUPLING CAPACITORS AS THEY WILL HAVE NO EFFECT ON THE $# CONDITIONS WITHIN THE AMPLIÚER 4HE TRANSISTOR IS A SILICON TYPE AND

569. AS WE MENTIONED EARLIER

570. THE DEVICE CONSISTS OF TWO 1 / JUNCTIONS 4HE COLLECTOR BASE JUNCTION IS REVERSE BIASED

571. WHILE THE BASE EMITTER JUNC TION IS FORWARD BIASED !S A RESULT

572. THE VOLTAGE DROP BE TWEEN THE BASE AND EMITTER WILL BE THE SAME AS THE FORWARD VOLTAGE DROP FOR ANY CONDUCTING SILICON DIODE

573. OR APPROXIMATELY 6 4HE VOLTAGE DROP ACROSS RESISTOR 2 WILL THUS BE q 6 OR 6 AND THE CURRENT ÛOWING IN IT THE BASE BIAS CURRENT CAN BE CALCULATED USING /HMmS LAW 'JH #JBT DBMDVMBUJPOT GPS UIF TJNQMF DPNNPOFNJUUFS BNQMJÜFS DJSDVJU 'JH SJHIU 4VQFSJNQPTJOH BO JOQVU TJHOBM PO UIF CJBT DVSSFOU JO 'JH % P$ , u )F THE TRANSISTOR HAS A CURRENT GAIN OF

574. WE CAN NOW ÚND THE STATIC VALUE OF COLLECTOR CURRENT USING %XUUHQW JDLQ, ,u u 7E CAN NOW DETERMINE THE VOLT AGE DROPPED ACROSS THE COLLECTOR LOAD

575. 2 .OW LETmS SUPERIMPOSE A SIGNAL CURRENT ONTO THE BIAS AND SEE WHAT HAPPENS TO THE COLLECTOR CURRENT 4O DO THIS

576. WE CAN USE THE TRANSFER CHARACTERISTIC THAT WE MET EARLIER 4HE NO SIGNAL OR QUIESCENT CONDI TION WHEN THE BASE CURRENT IS M! AND COLLECTOR CURRENT IS M! IS MARKED AS THE OPERATINGª POINT ON IG

577. WHICH ALSO SHOWS THE EFFECT OF SUPERIMPOSING A SIGNAL WHICH HAS A PEAK VALUE OF M! ON THE STEADY BIAS CURRENT $UE TO THE SIGNAL

578. THE BASE CURRENT WILL SWING UP TO M! ON POSITIVE PEAKS AND DOWN TO M! ON NEGA TIVE PEAKS )N RESPONSE TO THIS

579. THE COLLECTOR CURRENT WILL SWING UP TO M! AND DOWN TO M! 4HIS WILL HAVE THE EFFECT OF PRODUCING AN OUT PUT VOLTAGE CHANGE DROPPED ACROSS 3- OF 6 PEAK TO PEAK 0LEASE NOTEØ 4HE OPTIMUM VALUE OF COLLECTOR EMITTER VOLTAGE FOR THE COMMON EMITTER AMPLIÚER CIRCUIT SHOWN IN IG IS EXACTLY HALF THAT OF THE %, %,# P$u P$ / 99 u/9 9 ( / 99 9 9 (9#% 9 P$ worldmags worldmags

580. Everyday Practical Electronics, February 2011 51 Teach-In 2011 SUPPLY 4HIS ENSURES THAT THE VOLTAGE ATTHECOLLECTOROFTHETRANSISTOR IE

581. THE OUTPUT SIGNAL CAN SWING EVENLY UP TO 6 AND DOWN TO 6 WHEN THE SIGNAL IS APPLIED

582. RETURNING BACK TO 6 WHEN THE SIGNAL IS NO LONGER PRESENT )MPROVEDªAMPLIlERªSTAGES )N ORDER TO STABILISE THE OPERATING CONDITIONS FOR AN AMPLIÚER STAGE AND COMPENSATE FOR VARIATIONS IN TRANSIS TOR PARAMETERS

583. BASE BIAS CURRENT FOR THE TRANSISTOR CAN BE DERIVED FROM THE VOLTAGE AT THE COLLECTOR SEE IG 4HIS VOLTAGE IS DEPENDANT ON THE COL LECTOR CURRENT THAT

584. IN TURN

585. DEPENDS UPON THE BASE CURRENT ! NEGATIVEª FEEDBACK LOOP THUS EXISTS IN WHICH THERE IS A DEGREE OF SELF REGULATION )F THE COLLECTOR CUR RENT INCREASES

586. THE COLLECTOR VOLTAGE WILL FALL AND THE BASE CURRENT WILL BE REDUCED 4HE REDUCTION IN BASE CURRENT WILL PRODUCE A CORRESPOND ING REDUCTION IN COLLECTOR CURRENT TO OFFSET THE ORIGINAL CHANGE #ON VERSELY

587. IF THE COLLECTOR CURRENT FALLS

588. THE COLLECTOR VOLTAGE WILL RISE AND THE BASE CURRENT WILL INCREASE 4HIS

589. IN TURN

590. WILL PRODUCE A CORRESPOND ING INCREASE IN COLLECTOR CURRENT TO COMPENSATE FOR THE ORIGINAL CHANGE IG SHOWS A FURTHER IMPROVE MENT IN WHICH $# NEGATIVE FEEDBACK IS USED TO STABILISE THE STAGE AND COM PENSATE FOR VARIATIONS IN TRANSISTOR PARAMETERS

591. COMPONENT VALUES AND TEMPERATURE CHANGES 2ESISTORS 2 AND 2 FORM A POTENTIAL DIVIDER THAT DETERMINES THE $# BASE POTENTIAL

592. 7 4HE BASE EMITTER VOLTAGE 7% IS THE DIFFERENCE BETWEEN THE POTENTIALS PRESENT AT THE BASE 7 AND EMITTER 7% 4HE POTENTIAL AT THE EMITTER IS GOVERNED BY THE EMITTER CURRENT *% )F THIS CURRENT INCREASES

593. THE EMIT TER VOLTAGE 7% WILL INCREASE AND

594. AS A CONSEQUENCE 7% WILL FALL 4HIS

595. IN TURN

596. PRODUCES A REDUCTION IN EMIT TER CURRENT WHICH LARGELY OFFSETS THE ORIGINAL CHANGE #ONVERSELY

597. IF THE EMITTER CURRENT 7% DECREASES

598. THE EMITTER VOLTAGE 7% WILL INCREASE REMEMBER THAT 7 REMAINSCONSTANT 4HEINCREASEINBIAS RESULTSINANINCREASEINEMITTERCURRENT COMPENSATING FOR THE ORIGINAL CHANGE 4HEªTRANSISTORªASªAªSWITCH #ONVENTIONAL ELECTROMECHANICAL SWITCHES CAN ONLY OPERATE AT VERY LOW SPEEDS 4RANSISTORS

599. ON THE OTHER HAND

600. CAN SWITCH CURRENT MANY MIL LIONS OF TIMES FASTER AND WITHOUT ANY WEAR OR DETERIORATION IG 'JH O JNQSPWFE DPNNPOFNJUUFS BNQMJÜFS 'JH GVSUIFS JNQSPWFE DPNNPOFNJUUFS BNQMJÜFS 'JH TJNQMF USBOTJTUPS TXJUDI worldmagsworldmags worldmags

601. 52 Everyday Practical Electronics, February 2011 Teach-In 2011 SHOWS A SIMPLE TRANSISTOR SWITCHING CIRCUIT IN WHICH THE CURRENT IS BEING SWITCHED ON AND OFF IN THE LOAD

602. 3, )N IG A

603. NO BASE CURRENT IS AP PLIEDTOTHETRANSISTORANDTHETRANSISTOR ISINTHElOFFmSTATE)NTHISCONDITION

604. NO COLLECTOR CURRENT ÛOWS AND SIMILARLY NO CURRENT ÛOWS IN 3, )N IG B A BASE CURRENT OF M! IS APPLIED TO THE TRANSISTOR FROM A 6 SOURCE !S BEFORE

605. IF WE ASSUME THAT THE TRANSISTOR HAS A CURRENT GAIN OF

606. THE COLLECTOR CURRENT SHOULD BE M! TIMES THE BASE CURRENT (OWEVER

607. THISISNOTPOSSIBLEBECAUSE THECOLLECTORCURRENTCANNEVERBEMORE THAN M! DETERMINED BY THE 6 SUPPLY AND THE RESISTANCE OF THE LOAD )N THIS CONDITION

608. THE TRANSISTOR IS SAID TO BE SATURATED AND NO MORE COLLECTOR CURRENT WILL ÛOW REGARDLESS OF HOW MUCH MORE BASE CURRENT IS SUPPLIED 4RANSISTORS USED IN SWITCHING CIR CUITS ARE NORMALLY OPERATED UNDER SATURATION CONDITIONS 4HIS MEANS THAT THE COLLECTOR VOLTAGE WILL EITHER BE THE SAME AS THE SUPPLY VOLTAGE IN THE lOFFm STATE OR VERY CLOSE TO 6 IN THE lONm STATE ,ATER IN THIS INSTAL MENT OF 4EACH )N YOU WILL BE BUILD ING AND TESTING AN lASTABLEm CIRCUIT THAT USES TWO TRANSISTORS OPERATING AS SATURATED SWITCHES 6/ YOUmVE HEARD THE THEORY ABOUT TRANSISTORS q NOW LETmS TRY IT OUT IN #IRCUIT 7IZARD 7EmLL START OFF BY EXPLORING A COUPLE OF REALLY SIMPLE TRANSISTOR CIRCUITS TO SEE HOW THEY FUNCTION 9OU CAN ÚND TRANSISTORS IN THE l$ISCRETE 3EMICONDUCTORSm FOLDER IN THE GALLERY 9OUmLL NOTICE THAT THERE ARE LOTS OF DIFFERENT TYPES OF TRANSISTORS TO CHOOSE

609. INCLUDING STANDARD BIPOLAR AND ÚELD EFFECT TYPES !S WELL AS HAVING DIFFERENT TYPES OF TRANSISTOR

610. EACH CAN BE SET TO ONE OF A LARGE SELECTION OF DIFFERENT MODELS FOR THAT TYPE 4HERE ARE LITERALLY THOUSANDS OF DIFFERENT MODELS OF TRANSISTORS ON THE MARKET

611. ALL WITH DIFFERENT SHAPES

612. SIZES AND CHARACTERISTICS )TmS IMPORTANT THAT WHEN YOUmRE DESIGNING CIRCUITS THAT YOU For more information, links and other resources please check out ourTeach-In website at: www.tooley.co.uk/ teach-in Circuit Wizard A Standard or Professional version ofCircuitWizardcanbepurchasedfrom the editorial ofﬁce of EPE – see CD- ROMs for Electronics page and the UK shop on our website (www.epemag. com) for a ‘special offer’. Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developeralsooffersanevaluationcopy of the software that will operate for 30 days,althoughitdoeshavesomelimita- tions applied, such as only being able tosimulatetheincludedsamplecircuits and no ability to save your creations. However, if you’re serious about electronics and want to follow our series, then a full copy of Circuit Wizard is a really sound investment. #HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING 3KETCH THE CIRCUIT SYMBOL FOR A AN /1/ *4 AND B A 1/1 *4 AND LABEL THE CONNECTIONS 7HEN USED AS A SIMPLE COM MON EMITTER AMPLIÚER

613. WHAT VOLT AGE WOULD YOU EXPECT TO MEASURE BETWEEN THE BASE AND EMITTER OF A SILICON TRANSISTOR %XPLAIN YOUR ANSWER ! TRANSISTOR OPERATES WITH A COLLECTOR CURRENT OF M! AND A BASE CURRENT OF ! 7HAT WILL THE EMITTER CURRENT BE 7HAT WILL THE COMMON EMIT TER CURRENT GAIN BE FOR THE *4 IN 1UESTION 3KETCH THE CIRCUIT OF A SIMPLE COMMON EMITTER AMPLIÚER ,ABEL YOUR DIAGRAM %XPLAIN WHY CAPACITORS ARE NEEDED AT THE INPUT AND OUTPUT OF A SIMPLE *4 AMPLIÚER %XPLAIN WHY BIAS IS NEEDED IN A TRANSISTOR AMPLIÚER 3KETCH THE CIRCUIT OF A SIMPLE TRANSISTOR SWITCH %XPLAIN HOW THE CIRCUIT OPERATES ªªUILDªnª4HEª#IRCUITª7IZARDªWAY CHOOSE ONE THATmS RIGHT FOR THE JOB 7EmLL SEE WHAT DIFFERENCE IT MAKES BY TRYING OUT A CIRCUIT WITH TWO DIFFERENT TRANSISTOR MODELS 3TART OFF BY RECREATING THE CIRCUIT SHOWN IN IG USING AN /1/ TRANSISTOR /NCE YOUmVE DRAGGED THE TRANSISTOR ON TO YOUR CIRCUIT

614. DOUBLE CLICK THE SYMBOL AND SELECT # FROM THE MODEL DROP DOWN 4HE AMMETERS CAN BE FOUND IN THE lVIRTUAL INSTRUMENTSm FOLDER -AKE SURE THAT YOU GET THEM THE RIGHT WAY ROUND LOOK FOR THE POSITIVE

615. SYMBOL OR YOUmLL GET A NEGATIVE CURRENT READING /NE OF THE NEAT FEATURES IN #IRCUIT 7IZARD IS THAT YOU CAN POP VOLTMETERS AND AMMETERS INTO YOUR CIRCUIT DESIGNS SO THAT YOU CAN TAKE READ INGS AND SEE WHATmS GOING ON IN YOUR CIRCUIT WITH EASE worldmags worldmags

616. Everyday Practical Electronics, February 2011 53 Teach-In 2011 .OW RUN THE CIRCUIT AND ÛICK THE SWITCH .OT THE MOST INTERESTING OF CIRCUITS

617. BUT IT DOES SHOW US SOME KEY FEATURES OF A TRANSISTORmS OPERA TION 9OU MIGHT ALSO LIKE TO SWITCH TO THE l#URRENT LOWm VIEW TO SEE A VISUALISATION OF THE CURRENT MOVING AROUND THE CIRCUIT ,EAVE THE SWITCH CLOSED ON FOR THE MOMENT AND TAKE READINGS FOR *# AND * AND SEEING IF IT MATCHES UP TO YOUR READING FOR *% 4HENUMBEROFTIMESBIGGERTHELOAD CURRENT IS THAN THE INPUT CURRENT USED TO CONTROL THE TRANSISTOR IS CALLED THE GAIN7ECANCALCULATETHEGAINFOROUR TRANSISTOR USING THE FORMULA #URRENT GAIN MUCH LARGER CURRENT SUPPLIED TO THE MOTOR ,OOKING AT THE CIRCUITS YOU CAN SEE THAT PIN

618. THE OUTPUT OF THE IS GOING TO THE BASE OF THE TRAN SISTOR (ENCE

619. WHEN THE OUTPUT IS HIGH

620. A LITTLE CURRENT ÛOWS INTO THE BASE OF THE TRANSISTOR AND lTURNS IT ONm 4HIS ALLOWS CURRENT TO ÛOW DOWN FROM THE SUPPLY THROUGH THE MOTOR AND DOWN TO GROUND )N THIS CASE

621. THE TRANSISTOR IS USED AS A SWITCH

622. WITH THE TRANSISTOR EITHER BEING COMPLETELY lONm OR lOFFm 7HEN YOUmVE ENTERED THE CIR CUIT INTO #IRCUIT 7IZARD

623. CHANGE THE VIEW TO l6OLTAGE ,EVELSm LEFT HAND TABS

624. SEE IG AND LOOK CAREFULLY AT THE CURRENTS IN THE CIRCUIT

625. ESPECIALLY AROUND THE TRANSISTOR ªª4HEª#IRCUITª7IZARDªWAY OF DIRECTLY POWERING A LARGE LOAD LIKE A MOTOR 4HE MOST IT COULD HANDLE IS ÛASH ING AN ,%$ q SO THE QUESTION IS HOW CAN WE USE IT TO CONTROL SOMETHING MUCH MORE POWERFUL 7ELL

626. THE AN SWER IS BY USING A TRANSISTOR 7HAT WE DO IS USE A REALLY SMALL CURRENT COMING OUT OF THE TO CONTROL A A LOOK AT THE THREE AMMETER READINGS .OTICETHATTHEREISASMALLAMOUNTOF CURRENT ÛOWING INTO THE BASE OF THE TRANSISTOR

627. BUT THEREmS A MUCH LARGER CURRENTÛOWINGINTOTHECOLLECTORAND THROUGHTOTHEEMITTER)NCURRENTÛOW VIEW YOU CAN SEE THAT THE RIGHT HAND LOOP OF THE CIRCUIT IS MUCH THICKER 4HIS DEMONSTRATES HOW WE CAN USE TRANSISTORS TO CONTROL A MUCH LARGER CURRENT FROM A RELATIVELY SMALL ONE 4HE NEXT THING TO NOTICE IS THAT THE CURRENT ÛOWING OUT OF THE EMITTER IS EQUAL TO THE CURRENT ÛOWING INTO THE COLLECTOR

628. PLUS THE CURRENT ÛOWING IN TO THE BASE 7E CAN WRITE THIS US ING THE FORMULA THAT WE MET BEFORE *% * *# $OUBLE CHECK THIS PROVES TRUE FOR YOUR CIRCUIT BY ADDING YOUR 'JH 5SBOTJTUPS EFNPOTUSBUJPO DJSDVJU XJUI BNNFUFST UP TIPX DVSSFOU ÝPX 'JH 5SBOTJTUPSJTFE NPUPS DPOUSPM DJSDVJU 5SE THIS FORMULA TO HELP YOU CALCULATE THE GAIN FOR THE CIRCUIT 2EMEMBER TO USE *$ NOT * q ITmS A VERY COMMON MISTAKEØ .OW WEmVE PROVED A BIT OF THE ORY IN ACTION

629. LETmS SEE SOME REAL CIRCUITS THAT USE TRANSISTORS 7E DISCUSSED IN ,EARN

630. THAT TRANSIS TORS CAN BE USED AS A SWITCH OR AN AMPLIFIER q SO HEREmS AN EXAMPLE OF EACH 4RANSISTORªSWITCHINGªCIRCUIT %NTER AND SIMULATE THE TRANSISTOR SWITCHING CIRCUIT SHOWN IN IG 4HIS CIRCUIT USES A TIMER CHIP WEmLL BE LOOKING AT THESE IN DETAIL A LITTLE LATER IN THE SERIES TO PULSE A $# MOTOR 4HE PROBLEM WE HAVE IS THAT ALTHOUGH THE IS A CLEVER LITTLE CHIP

631. ITmS A BIT PUNY AND NOT CAPABLE % , , # worldmagsworldmags worldmags

632. 54 Everyday Practical Electronics, February 2011 Teach-In 2011 4RANSISTORªAMPLIlERªCIRCUIT )N THE NEXT CIRCUIT

633. WE ARE GOING TO SEE A TRANSISTOR OPERATING AS AN AMPLIÚER 4HIS WILL ALSO INTRODUCE US TO SOME OF THE GRAPHING FACILITIES IN CIRCUIT WIZARD 3TART OFF BY ENTERING THE CIRCUIT SHOWN IN IG INTO #IRCUIT 7IZARD -AKE SURE THAT YOU DONmT CONFUSE VOLTAGE RAILS FOUND IN l0OWER 3UP PLIESm AND A TERMINAL FOUND IN l#ONNECTORSm 4O LABEL THE LATTER

634. JUST DOUBLE CLICK ON THEM AND ENTER A NAME

635. BUT NOTE THAT NAMING A TER MINAL l6m OR l6m DOES NOT TURN IT IN TO A VOLTAGE RAILØ -AKE SURE THAT YOU CHANGE DEFAULT VALUES FOR THE COMPONENTS AND FUNCTION GENERATOR TO MATCH THE DIAGRAM GIVEN ªª4HEª#IRCUITª7IZARDªWAY 'JH 5SBOTJTUPSJTFE NPUPS DPOUSPM DJSDVJU TJNVMBUFE JO m7PMUBHF -FWFMTn WJFX /NCE YOU HAVE THE CIRCUIT MADE UP YOUmLL NEED TO ADD SOME PROBES $O THIS BY CLICKING ON THE PROBE l!DD 0ROBEm BUTTON ON THE TOOLBAR SEE IG

636. THEN DROPPING THE PROBE WHERE YOU WOULD LIKE IT TO GO !DD ONE PROBE RED TO THE OUTPUT AND ONE BLUE ON TO THE INPUT JUST AFTER THE FUNCTION GENERATOR !S YOU PLACE MORE PROBES IT WILL AUTOMATI CALLY GIVE THEN A NEW COLOUR SO THAT YOU CAN IDENTIFY THEM LATER ON !S YOU PLACE YOUR ÚRST PROBE YOU SHOULD NOTICE THAT A GRAPH WILL APPEAR ALONG THE BOTTOM OF THE SCREEN 4HIS IS GREAT FOR ALLOWING YOU TO MONITOR HOW VOLTAGES AROUND YOUR CIRCUIT CHANGE OVER TIME EFORE YOU HIT lSIMULATEm DOUBLE CLICK ON THE GRAPH AND CHANGE THE GRAPH PROPERTIES TO THOSE SHOWN IN IG 4HIS WILL SET THE MINIMUM AND MAXIMUM VOLTAGES SHOWN ON THE GRAPH SEE IG AND THE TIME SCALE TO GIVE YOU A NICE LOOKING TRACE FROM THE CIRCUIT .OW SIMULATE THE CIRCUIT AND KEEP AN EYE ON THE GRAPH 9OU SHOULD SEE TWO SINUSOIDAL WAVES TRACED OUT SEE IG 4HE ÚRST BLUE LINE IS THE INPUT q IT HAS A RE ALLY SMALL AMPLITUDE YOU CAN BARELY 'JH EE QSPCF CVUUPO 'JH (SBQI QSPQFSUJFT EJBMPHVF GPS UIF USBOTJTUPS BNQMJÜFS DJSDVJU 'JH 4JNQMF 5SBOTJTUPS BNQMJÜFS DJSDVJU worldmags worldmags

637. Everyday Practical Electronics, February 2011 55 Teach-In 2011 SEE IT RISING ABOVEDIPPING BELOW THE AXIS 4HE RED LINE HOWEVER

638. IS A MUCH LARGER VERSION OF THE BLUE LINE 4HIS IS THE AMPLIÚED OUTPUT SIGNAL )T HAS A MUCH HIGHER AMPLITUDE THAN THE INPUT SIGNAL )N THIS CIRCUIT

639. THE TRANSISTOR ACTS AS AN AMPLIÚER 4HE TRANSISTOR IS BEING PROGRESSIVELY SATURATED BY THE SMALL SIGNAL INPUT AND SO THE OUTPUT VARIES COINCIDENTLY TO THE INPUT )TmS ACTING A BIT LIKE A TAP BEING OPENED AND CLOSED TO CONTROL THE ÛOW OF CURRENT IN THE OUTPUT !STABLEªOSCILLATORªCIRCUIT .OW WEmRE GOING TO STEP THINGS UP A LITTLE AND ENTER ANOTHER USEFUL REAL WORLD CIRCUIT INTO #IRCUIT 7IZARD 4HE CIRCUIT SHOWN IN IG IS A SIMPLE CIRCUIT THAT ÛASHES TWO ,%$S ALTERNATELY 4O GIVE IT ITS CORRECT NAME ITmS AN ASTABLEª OSCILLATOR CIRCUIT BECAUSE IT TURNS ON AND OFF CONTINUOUSLY )T USES A PAIR OF TRANSISTORS THAT CONTROL THE CHARGING AND DISCHARGING OF TWO CAPACITORS ALTERNATELY q A LITTLE LIKE A SEE SAW %NTER THE CIRCUIT SHOWN IN IG

640. MAKING SURE THAT YOU GET ALL OF THE COMPONENT VALUES CORRECT

641. AND THEN HIT THE PLAY BUTTON ON THE TOP BAR TO START THE SIMULATION $ID IT WORK 4RY OUT THE DIFFERENT DISPLAY STYLES BY CLICKING THE TABS ALONG THE LEFT OF THE SCREEN THE lCURRENT ÛOWm DISPLAY SEE IG WORKS REALLY WELL SHOWING HOW THE CURRENT IS ÛOWING AROUND THE CIRCUIT

642. WITH THE COLOUR SHOWING THE VOLTAGE SEE SAWING ON EITHER SIDE OF THE CIRCUIT AND THE CHARGES BUILDINGDIMINISH ING ON THE CAPACITORS INALLY

643. SAVE YOUR CIRCUIT AS WEmLL BE USING THEM TO CONSTRUCT A PRINTED CIRCUIT BOARD LAYOUT LATER ON ªª4HEª#IRCUITª7IZARDªWAY 'JH YBNQMF USBDF GSPN USBOTJTUPS BNQMJÜFS DJSDVJU 5IF PVUQVU XBWFGPSN JT TIPXO BU UIF UPQ BOE UIF JOQVU XBWFGPSN BU UIF CPUUPN 'JH 5XP USBOTJTUPS BTUBCMF PTDJMMBUPS DJSDVJU 'JH 5SBOTJTUPS BTUBCMF PTDJMMBUPS JO DVSSFOU ÝPX EJTQMBZ TUZMF worldmagsworldmags worldmags

644. 56 Everyday Practical Electronics, February 2011 Teach-In 2011 4HE CIRCUIT OF A SIMPLE AUDIO AM PLIÚER IS SHOWN IN IG 3TUDY THE CIRCUIT CAREFULLY

645. LOOK BACK AT WHAT WE DID IN 4EACH )N 0ART TO 0ART

646. AND THEN SEE IF YOU CAN ANSWER EACH OF THE FOLLOWING QUESTIONS 7HAT TYPE OF TRANSISTOR IS A 42 AND B 42 7HAT OPERATING MODE IS USED FOR A 42 AND B 42 7HAT TYPE OF DIODE IS $

647. AND WHAT VOLTAGE WOULD YOU EXPECT TO MEASURE ACROSS IT 4HE MAINS OPERATED POWER SUP PLY FOR THE AMPLIÚER IS RATED AT 7 7ILL THIS BE SUFÚCIENT %XPLAIN YOUR ANSWER 7HAT TYPE OF CAPACITOR IS #

648. AND WHAT SHOULD ITS RATED WORKING VOLTAGE BE 7HAT COLOUR CODE SHOULD APPEAR ON A 2

649. B 2 AND C 2 )F A POTENTIAL DROP OF 6 AP PEARS ACROSS 2

650. WHAT CURRENT WILL BE ÛOWING IN IT 7HAT IS THE TIME CONSTANT OF THE SERIES CIRCUIT FORMED BY # AND 2 3O FAR IN 4EACH )N WEmVE BEEN USING #IRCUIT 7IZARD TO SIMULATE A VARIETY OF SIMPLE ELECTRONIC CIRCUITS SO THAT WE CAN BETTER UNDERSTAND HOW THEY WORK (OWEVER

651. YOU MAY BEWONDERINGHOWWEGETFROMSOME THING THAT LOOKS NICE ON A COMPUTER SCREEN TO SOMETHING THAT WE CAN ACTUALLY BUILD AND USE 7ELL

652. #IRCUIT 7IZARD HAS A SUPERB SET OF TOOLS TO HELPS US DO JUST THAT ,OAD UP THE TRANSISTOR ASTABLE CIRCUIT THAT YOU MADE IN OUR lUILDm TUTORIAL 4HEN CLICK ON THE l#ONVERT TO 0# ,AYOUTm BUTTON ON THE TOOLBAR SEE IG 4HIS WILL INITIATE A SIMPLE WIZARD THAT LETS YOU CONVERT A CIRCUIT DESIGN INTO A PRINTED CIRCUIT BOARD 0# !MAZE)NVESTIGATE 'JH 4FF RVFTUJPOT CFMPX 'JH $POWFSU UP 1$# CVUUPO 'JH 4FMFDUJOH 1$# UZQF worldmagsworldmags worldmags

653. Everyday Practical Electronics, February 2011 57 Teach-In 2011 DESIGN THAT YOU CAN THEN TEST lVIRTU ALLYmANDORCREATEARTWORKTOPRODUCE THE 0# FOR REAL 3TEPTHROUGHTHEWIZARDBYCLICKING l.EXTm WEmLL LEAVE THE DEFAULT SETTING FOR THE MOMENT 9OU WILL THEN BE ASKED TO CHOOSE A 0# LAYOUT q SELECT l3INGLE 3IDED .ORMAL 4RACKSm SEE IG INALLY

654. CLICKONTHEl#ONVERTmBUTTON

655. THEN SIT BACK

656. CROSS YOUR ÚNGERS AND LET #IRCUIT 7IZARD WORK ITmS MAGICØ )F ALL GOES WELL

657. YOU SHOULD SEE THE COM PONENTS BEING PLACED ON TO THE CIRCUIT BOARDANDTHENTHETRACKSAUTOMATICALLY ROUTED RIGHT BEFORE YOUR EYES 7HEN ITmS COMPLETED CONVERTING YOUR CIRCUIT IT WILL POP UP A WINDOW TELLING YOU HOW SUCCESSFUL ITmS BEEN HOPEFULLY IT WILL REPORT THAT OF THE CONNECTIONS HAVE BEEN MADE #LICK ON /+ AND ADMIRE YOUR 0# DESIGN #IRCUIT 7IZARD GIVES YOU A REALLY NICE l2EAL 7ORLDm VIEW OF WHAT YOUR PRODUCED CIRCUIT WOULD LOOK LIKE .OW TRY SOME OF THE OTHER VIEWS ALONG THE LEFT 4HERE ARE A NUMBER OF THINGS THAT YOU CAN NOW DO WITH YOUR DESIGN )F YOU WANT TO GO AHEAD AND PRODUCE YOUR CIRCUIT YOU CAN EASILY PRINT OUT YOUR ARTWORK MASK TO USE !LTERNA TIVELY

658. YOU CAN TRY OUT YOUR 0# AND TEST IT VIRTUALLY *USTASINREALLIFE

659. YOUNEEDABATTERY TO OPERATE THE CIRCUIT 'RAB ONE FROM THE l/FF OARD #OMPONENTSm

660. l0OWER 3UPPLIESm FOLDER IN THE GALLERY )N THIS CASE YOUmLL NEED A 6 00 ALTERNA TIVELYYOUCOULDUSETHEVIRTUALPOWER SUPPLYFROMl6IRTUAL4EST%QUIPMENTm #ONNECT UP YOUR BATTERY AS SHOWN IN IG

661. ANDTESTYOUR0#BYSTARTING THE SIMULATION %XPERIMENT WITH THE VIRTUAL MULTI METER TO CHECK SOME OF THE VOLTAGES AROUND THE CIRCUIT 4HE DISPLAY STYLES ALSO WORK WITH A 0# SO TRY SOME OF THESE OUT TOO .EXT MONTHØ )N NEXT MONTHmS 4EACH )N WE WILL LOOK AT INTEGRATED CIRCUITS )#S AND OPERATIONAL AMPLIÚERS OP AMPS 'JH $IFDLJOH PVU UIF XPSLJOH BTUBCMF DJSDVJU !NSWERSªTOª1UESTIONS 3EE IG 6 AS THIS IS THE USUAL FORWARD VOLTAGE FOR A CONDUCTING 1 / JUNCTION M! 3EE IG 3EE PAGE 3EE PAGE 3EE PAGE By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! ,58,7 :,=$5' 6SHFLDO (3( 2IIHU Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard – which is on special offer from EPE – and Professional. Special EPE Offer ends 31 Jan, 2011 Special EPE Offer - Standard version only. EPE is offering readers a 10% discount on Cicuit Wizard Standard software if purchased before 31 Jan, 2011. This is the software used in our Teach-In 2011 series. Standard (EPE Special Offer) £59.99 £53.99 inc. VAT Professional £89.99 inc. VAT * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export worldmagsworldmags worldmags

662. 48 Everyday Practical Electronics, March 2011 Teach-In 2011 By Mike and Richard Tooley 0ARTªª/PERATIONALªAMPLIlERS /URª4EACH )NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROAD BASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEª ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª4%#ª,EVELªªAWARDS

663. ªASªWELLªASªELECTRONICSª UNITSªOFªTHEªNEWª$IPLOMAªINª%NGINEERINGª ALSOªATª,EVELª ª4HEªSERIESªWILLªALSOªPROVIDEªTHEªMOREªEXPERIENCEDª READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUP ªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª %ACHªPARTªOFªOURª4EACH )NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARN

664. ª#HECK

665. ªUILD

669. ªANDªlNALLY

670. ª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTOR ªª TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS ,EARN Circuit Wizard to simulate a variety OF OPERATIONAL AMPLIÚER CIRCUITS

671. while Investigate challenges you to explain the operation of a simple OSCILLATOR CIRCUIT INALLY

672. IN Amaze

673. we shall look back at the technology that we used before integrated circuits became available. I NTEGRATED circuits (ICs) comprise large numbers of transistors and other components built on a single small slice of silicon. 4HIS ALLOWS COMPLEX CIRCUITS

674. SUCH AS A COMPLETE RADIO RECEIVER

675. TO BE built in a package that’s smaller THAN THE NAIL ON YOUR LITTLE ÚNGER !NY ADDITIONAL COMPONENTS

676. SUCH as inductors and capacitors (dif- ÚCULT TO MANUFACTURE IN INTEGRATED circuit form) and other components that need to be externally accessible are then connected as external ‘discrete’ components. In this instalment of Teach-In 2011

677. WE WILL BE INVESTIGATING ONE OF the most common types of integrated CIRCUIT

678. THE OPERATIONAL AMPLIÚER op amp). In Build

679. YOU WILL BE USING )NTEGRATEDªCIRCUITS Used in a huge variety of different APPLICATIONS

680. OPERATIONAL AMPLIÚERS are probably the most common and versatile form of analogue integrated circuit. Fig.5.1showstheubiquitous OPERATIONAL AMPLIÚER

681. WHILE IG 5.2 shows what’s inside the 8-pin dual-in-line package. Fig.5.1. The famous 741 operational BNQMJÜFS XIJDI JT TVQQMJFE JO BO QJO EVBMJOMJOF QBDLBHF

682. Everyday Practical Electronics, March 2011 49 Teach-In 2011 You can think of an operational AMPLIÚER AS A UNIVERSAL lGAIN BLOCKm TO WHICH A FEW EXTERNAL COMPONENTS ARE ADDED IN ORDER TO DEÚNE THE PARTICULAR FUNCTION OF A CIRCUIT OR EXAMPLE

683. BY ADDING JUST TWO EXTERNAL RESISTORS

684. YOU CAN PRODUCE AN AMPLIÚER HAVING A PRECISELY DEÚNED GAIN ROM THIS YOU MIGHTBEGINTOSUSPECTTHATOPERATIONAL AMPLIÚERS ARE REALLY EASY TO USE 4HE GOOD NEWS IS THAT THEY AREØ Op amp 4HE SYMBOL FOR AN OPERATIONAL AM- PLIÚERISSHOWNINIG4HEREAREA FEWTHINGSYOUNEEDTONOTEABOUTTHIS 4HE DEVICE HAS TWO INPUTS AND ONE output and no common connection. .OTICE ALSO THAT ONE OF THE INPUTS IS MARKED lqm AND THE OTHER IS MARKED lm 4HESEPOLARITYMARKINGSHAVENOTHINGTO DO WITH THE SUPPLY CONNECTIONS q THEY INDICATETHEOVERALLPHASESHIFTBETWEEN EACH INPUT AND THE OUTPUT 4HE lm SIGN INDICATES ZERO PHASE SHIFT WHILE THE lqm SIGN INDICATES ˆ PHASE SHIFT 3INCE ˆ PHASE SHIFT PRODUCES AN INVERTED IE

685. TURNED UPSIDE DOWN WAVEFORM

686. THElqmINPUTISOFTENREFERRED TOASTHElinvertinginputm3IMILARLY

687. THE lm INPUT IS KNOWN AS THE lnon- invertingm INPUT URTHERMORE

688. WE OFTEN DONmT SHOW THE SUP- PLY CONNECTIONS AS IT IS OFTEN CLEARERTOLEAVETHEMOUTOFTHE CIRCUIT ALTOGETHER AND JUST AS- SUME THAT THEY ARE CONNECTED TO EVERY CHIPØ -OST BUT NOT ALL OPERA- TIONAL AMPLIÚERS REQUIRE A SYMMETRICAL SUPPLY OF TYPI- CALLYBETWEEN ‰6AND ‰6 4HISALLOWSTHEOUTPUTVOLTAGE TO SWING BOTH POSITIVE ABOVE 6 AND NEGATIVE BE- LOW 6 IGURE SHOWS HOW THE SUPPLY CONNECTIONS WOULD appear if we decided to include them. Note THAT WE USUALLY HAVE TWO SEPARATE SUPPLIES A POSITIVE SUPPLY AND AN EQUAL

689. BUT OPPOSITE

690. NEGATIVE SUPPLY 4HE common connection TO THESE TWO SUPPLIES IE

691. THE 6 RAIL ACTS AS the common rail in our CIRCUIT 4HE INPUT AND Fig.5.2. Internal circuit of the 741 operational BNQMJÜFS PQ BNQ 'JH 4ZNCPM GPS BO PQFSBUJPOBM BNQMJÜFS 'JH 4VQQMZ SBJMT GPS BO PQFSBUJPOBM BNQMJÜFS

692. 50 Everyday Practical Electronics, March 2011 Teach-In 2011 is the short-circuit output current (in amps). Example 1 !N AMPLIÚER PRODUCES AN OUTPUT VOLTAGE OF 6 WHEN SUPPLIED WITH AN input of 4mV. Determine the value of VOLTAGE GAIN OF THE AMPLIÚER Solution Now: OUTPUT VOLTAGES ARE USUALLY MEASURED relative to this rail. Gain Before we take a look at some of the characteristics of operational AMPLIÚERS

693. IT IS IMPORTANT TO DEÚNE SOME OF THE TERMS AND PARAMETERS THAT WE APPLY TO AMPLIÚERS GENERALLY One of the most important of these is THE AMOUNT OF AMPLIÚCATION OR lgain’ THATADEVICEPROVIDES4OKEEPTHINGS as simple as possible we will use an lEQUIVALENT CIRCUITm TO REPRESENT AN AMPLIÚER

694. AS SHOWN IN IG 4HIS is much easier to work with than the CIRCUIT THAT WE MET EARLIER IN IG )N IG THE AMPLIÚER IS REPRE- SENTEDBYAlBLACKBOXm

695. WITHTWOINPUT AND TWO OUTPUT TERMINALS .OTE THAT IN PRACTICE

696. ONE OF THE INPUT TERMINALS IS OFTEN DIRECTLY LINKED TO ONE OF THE OUTPUT TERMINALS AND THEN REFERRED TO AS lCOMMONm 4HE INPUT RESISTANCE (Rin INIG ISTHERESISTANCETHATWE WOULDlSEEmLOOKINGINTOTHETWOINPUT TERMINALS

697. WHILETHEOUTPUTRESISTANCE (Rout IN IG IS THE RESISTANCE THAT WE WOULD lSEEm LOOKING BACK INTO THE TWO OUTPUT TERMINALS 4HE VOLTAGE PRODUCED BY THE AMPLIÚER IS SHOWN AS A lCONSTANT VOLTAGE GENERATORm THE CIRCLE WITH THE SINEWAVE INSIDE Gain is simply the ratio of what WE GET OUT TO WHAT WE PUT IN 3O

698. FOR EXAMPLE

699. VOLTAGE GAIN IS DEÚNED AS the ratio of output voltage to input VOLTAGE !S A FORMULA

700. THIS IS INALLY

701. THE POWER GAIN OF THE AMPLIÚER IS DEÚNED AS THE RATIO OF output power to input power. As a FORMULA

702. THIS IS where Av REPRESENTS VOLTAGE GAIN AND Vout AND Vin ARE THE OUTPUT AND INPUT voltages respectively. 3IMILARLY

703. CURRENT GAIN IS DEÚNED as the ratio of output current to input CURRENT !S A FORMULA

704. THIS IS out v in V A V = out i in I A I = where Ai REPRESENTS CURRENT GAIN AND Iout AND Iin ARE THE OUTPUT AND INPUT current respectively. out p in P A P = where Ap REPRESENTS VOLTAGE GAIN AND Pout AND Pin ARE THE OUTPUT AND INPUT voltages respectively. .OW POWER IS THE PRODUCT OF VOLT- AGE AND CURRENT

705. THUS out out outP I V= × and in in inP I V= × Combining these relationships gives: out out p i v in in I V A A A I V = = × 4HIS TELLS US THAT THE power gain OF AN AMPLIÚER IS THE product of the current gain AND voltage gain. Input resistance 4HE input resistance OF AN AMPLIÚER IS DEÚNED AS THE RATIO OF INPUT VOLTAGE to input current: in in in V R I = where Rin is the input resistance (in OHMS

706. Vin istheinputvoltage(involts) AND Iin is the input current (in amps). Output resistance 4HE output resistance of an ampli- ÚER IS DEÚNED AS THE RATIO OF OPEN circuit output voltage to short-circuit OUTPUT CURRENT 4HUS out(oc) out out(sc) V R I = where Rout is the output resistance IN OHMS

707. Vout(oc) is the open-circuit OUTPUT VOLTAGE IN VOLTS AND Iout(sc) out v in V A V = 4HUS 3 v 3 2 2 10 500 4 10 4 A − × = = = × Example 2 !N AMPLIÚER HAS AN INPUT RESISTANCE of 2M: 7HAT CURRENT WILL ÛOW INTO THE INPUT OF THE AMPLIÚER WHEN A VOLT- AGE OF M6 IS APPLIED Solution Now: in in in V R I = 4HUS 3 in in 6 in 50 10 2 10 V I R − × = = = × × Please note! %QUIVALENT CIRCUITS PROVIDE US WITH A WAY OF UNDERSTANDING THE BEHAVIOUR OF ELECTRONIC DEVICES AND CIRCUITS operate. /PERATIONALªAMPLIlERª characteristics (AVING NOW DEÚNED THE PARAMETERS THAT WE USE TO DESCRIBE AMPLIÚERS

708. IT IS WORTH CONSIDERING THE CHARACTERISTICS 'JH RVJWBMFOU DJSDVJU PG BO BNQMJÜFS 9 25 10 A = 25 nA− = × nA and

709. Everyday Practical Electronics, March 2011 51 Teach-In 2011 thatwewouldassociatewithan‘ideal’ (a) The voltage gain should be as largeaspossible,sothatalargeoutput voltage will be produced by a small input voltage (b)Theinputresistanceshouldbeas large as possible, so that only a small input current will be taken from the signal source (c) The output resistance should be aslowaspossible,soasnottolimitthe outputcurrentandpowerdeliveredby (d) Bandwidth should be as wide as possible so as not to limit the fre - Fortunately,thecharacteristicsofmost close to those of an ‘ideal’ operational bandwidthofmakingtheclosed-loop gains equal to 10,000, 1,000, 100, and 10. Table 5.2 summarises these results.Youshouldalsonotethatthe (gain × bandwidth) product for this 6Hz (ie, 1MHz). We can determine the bandwidth voltagegainissettoaparticularvalue by constructing a line and noting the .evrucesnopserehtnotnioptpecretni Please note! Theproductofgainandbandwidth - stant. Thus an increase in gain can only be achieved at the expense of bandwidth, and vice versa . Please note! When negative feedback is applied produce a negative output voltage, and vice versa ). To preserve symmetry and minimise offset voltage, a third resis - tor is often included in series with the non-inverting input. The value of this resistorshouldbeequivalenttothepar - allelcombinationof RIN and RF.Hence: Parameter Ideal Typical Voltage gain Very high 100,000 Input resistance Very high 100MΩ Output resistance Very low 20Ω Bandwidth Very wide 2MHz Table 5.1. Ideal and typical characteristics Gain and bandwidth It is important to note that the product of gain and bandwidth is a constant for any particular opera - increaseingaincanonlybeachieved attheexpenseofbandwidth,and vice versa .Inpractice,wecontrolthegain (and bandwidth) of an operational of negative feedback . Figure 5.6 shows the relationship between voltage gain and bandwidth (note that the axes use logarithmic, rather than linear scales). The open- loop voltage gain (ie, that obtained with no external feedback applied) is 100,000 and the bandwidth obtained in this condition is a mere 10Hz. The effect of applying increasing amounts ofnegativefeedback(andconsequent - lyreducingthegaintoamoremanage - able amount) is that the bandwidth increases in direct proportion. Frequency response The frequency response curves in Fig.5.6 show the effect on the Voltage gain (AV) Bandwidth 1 DC to 1MHz 10 DC to 100kHz 100 DC to 10kHz 1000 DC to 1kHz 10000 DC to 100 Hz 100000 DC to 10 Hz Table 5.2. Relationship between voltage gain and with a gain-bandwidth product of 1MHz reduced and the bandwidth is in - creased. When positive feedback is gain increases and the bandwidth is reduced.Inmostcasesthiswillresult in instability and oscillation. The three basic configurations are shown in Fig.5.7. As mentioned earlier, supply rails have been omit - ted from these diagrams for clarity but are assumed to be symmetrical about 0V. The voltage gain for the inverting by the expression: Fig.5.6.Frequencyresponsecurvesfor Thevoltagegainforthenon-invert - given by the expression: out F V in IN 1 V R A V R = = + Finally, the voltage gain for the dif - is given by the expression: VA = out F in IN V R V R − = − R F IN F IN R R R R × = + The minus sign in the voltage gain expression is included to indicate in - version(ie,apositiveinputvoltagewill out out F V in 2 1 IN V V R A V V V R = = = −

710. 52 Everyday Practical Electronics, March 2011 Teach-In 2011 Where V 1 and V 2 are the voltages at the input resistance ( RIN ) connected toinvertingandnon-invertinginputs respectively. Limit capacitor - scribed previously have used direct coupling and thus have frequency response characteristics that extend to DC. This, of course, is undesirable for many applications, particularly where a wanted AC signal may be superimposed on an unwanted DC voltage level. In such cases a capacitor of ap - propriate value may be inserted in series with the input, as shown below. The value of this capacitor should be chosen so that its reac - tance is very much smaller than the input resistance at the lower applied input frequency. We can also use a capacitor to re - stricttheupperfrequencyresponseof is connected as part of the feedback path. Indeed, by selecting appropri - ate values of capacitor, the frequency response of an inverting operational tailored to suit individual require - ments (see Fig.5.8 and Fig.5.9). The lower cut-off frequency is determined by the value of the input capacitance, C1,andinputresistance, R1. The lower cut-off frequency is given by: Provided the upper frequency re - sponse it not limited by the gain × bandwidth product, the upper cut-off frequency will be determined by the feedback capacitance, C2, and feed - back resistance, R2, such that: Where C2 is in Farads and R2 is in ohms. Example 3 is to be designed to the following Voltage gain = 20 Input resistance (at mid-band) = 10k ? Lower cut-off frequency = 100Hz Upper cut-off frequency = 10kHz Devise a circuit to satisfy the above Solution Tomakethingsalittleeasier,wecan breaktheproblemdownintomanage - able parts. We shall base our circuit - lower cut-off frequencies, as shown in the Fig.5.8. The nominal input resistance is the same as the value for R1. both the low and the high frequency response 1 1 0.159 2 1 1 1 1 f C R C Rπ = = 1 1 0.159 2 2 2 2 2 f C R C Rπ = = Thus: R1 = 10 kΩ Todeterminethevalueof R2wecan make use of the formula for mid-band voltage gain: AV = R2/R1 Thus: kΩ sR2 = Av × R1 = 20 × 10 kΩ = 200 kΩkΩ kΩ kΩ Where C1 is in farads and R1 is in ohms.

711. Everyday Practical Electronics, March 2011 53 Teach-In 2011 Todeterminethevalueof C1wewill use the formula for the low frequency cut-off: 1 0.159 1 1 f C R = From which: 3 1 0.159 0.159 1 0.159 10 F 159 nF 1 100 10 10 1 10 C f R = = = = × = × × × 6 6 0.159 0.159 10 F 159 1 10 − = = × = × nF Finally, to determine the value of C2 we will use the formula for high frequency cut-off: 2 0.159 2 2 f C R = in Fig. 5.10. Other applications As well as their application as a general purpose amplifying device, of other uses. We shall conclude this month’s Learn by taking a brief look attwoofthese, voltagefollowers and comparators . Avoltagefollowerusinganoperation - circuit is essentially a non-inverting isfedbacktotheinput.Theresultisan ‘unity’),averyhighinputresistanceand averyhighoutputresistance.Thisstage isoftenreferredtoasabufferandisused for matching a high-impedance circuit to a low-impedance circuit. Typicalinputandoutputwaveforms for a voltage follower are shown in Fig.5.12. Notice how the input and output waveforms are both in-phase (they rise and fall together) and that they are identical in amplitude. A comparator using an operational no negative feedback has been ap - plied, this circuit uses the maximum Fig.5.11. A voltage follower Fig.5.12. Typical input and output waveforms for a voltage follower Fig.5.13. A comparator Fig.5.14. Typical input and output waveforms for a comparator The output voltage produced by the the maximum possible value (equal to the positive supply rail voltage) whenever the voltage present at the non-inverting input exceeds that present at the inverting input. Con - versely, the output voltage produced totheminimumpossiblevalue(equal to the negative supply rail voltage) whenever the voltage present at the inverting input exceeds that present at the non-inverting input. From which: 3 3 9 2 0.159 0.159 0.159 2 0.159 10 F 159 pF 2 10 10 100 10 1 10 C f R = = = = × = × × × ×2 9 0.159 1 10 = ×2 0.50.159= × × 9 10 F 1− × =80pF 80

712. 54 Everyday Practical Electronics, March 2011 Teach-In 2011 Typical input and output wave - forms for a comparator are shown in Fig.5.14. Notice how the output is either +15V or –15V depending on the relative polarity of the two inputs. N OW we’ve heard the theory, let’s use Circuit Wizard to try outsomepracticaloperationalam - reallyneatwaytoexplorethiskind of theory because students often prototyping boards. Thismightbeduetoneedingdual rail power supplies, or the fact that the schematic diagram into a ‘real life’ circuit where incorrect layout can cause confusing results! Fortu - nately, we can do away with these problems when investigating these devices using Circuit Wizard. So let’slookatasimpleoperationalam - Please note! W hen capturing a schematic based onoperationalam - plifiers it is im - portant to double check the orien - tation of the two signal input pins. By default, Circuit Wizard will draw anoperationalam - plifier with the non-inverting in - put (labelled ‘+’) at the top and the non-inverting in - put (labelled ‘−‘) at the bottom. This may or may not be the same as the circuit you are entering – so make sure that you double check! Fortunately, it’s really easy to change this; just right-click the op amp and click ‘arrange’ then ‘mir - ror’ (see Fig.5.15). It is important to note that by ‘mirroring’ the op amp, the supply connections re - main unchanged, ie the positive supply at the top and negative at the bottom. Withtheforegoinginmind,enter thecircuitshowninFig.5.16.Inthis circuit we have a 2V variable input voltage connected to our invert - ing input, with our non-inverting input connected to ground (0V). Recalling what we learned earlier, Check – 5.1. Sketch the circuit symbol for of the connections. 5.2. Sketch an equivalent circuit and output resistances. Label your drawing . 5.3. List four desirable characteris - . 5.4. - putof1.5Vwhenaninputof7.5mV is present. Determine the value of the voltage gain. 5.5. of 50 and a current gain of 2,000. W hat power gain does the ampli - 5.6. Sketch the circuit of an invert - - and identify the components that determine the voltage gain of the . 5.7. Aninvertingoperationalampli - gain of –15, an input resistance of 5k? , and a frequency response ex - tendingfrom20Hzto10kHz.Devise a circuit and specify all component values required. you are doing? How do you think The Circuit Wizard way thecorrectorientationofinvertingandnon-inverting inputs For more information,links and other resources please check out ourTeach-In website at: www.tooley.co.uk/ teach-in

713. Everyday Practical Electronics, March 2011 55 Teach-In 2011 we know that the basic principle of the difference in voltage between the two inputs. - videdbythecircuitshowninFig.5.16 is determined by the gain, which will dependonthearrangementandvalues oftheresistorsinthecircuit.Welearnt that we can calculate the gain of an the formula: In our circuit, RF (R2) is 2.5k ? and RIN (R1) is 500 ? . Use the formula above to prove that the gain of this circuit is –5. In simple terms, this means that we should expect our output voltage to be –5 times larger thantheinputvoltage.Notetheminus sign;theoutputwillbeinverted,asits name suggests. Nowsettheinputvoltageto1Vand run the simulation. We would expect theoutputvoltagetobe−5×1V=−5V. Nowexperimentwithchangingthein - putvoltageandmonitoringtheoutput voltage. You should see that the gain holds true whatever the input voltage upuntiltheoutputreachesthesupply voltage.Atthispoint,theoutputvolt - age will remain constant, even with increased input voltage. Whereas this used in audio circuits this can cause clipping of the waveform, which can distort the sound. Modifyyourcircuitbyreplacingthe variableinputvoltagewithafunction generator and adding some probes, as showninFig.5.17.Thewaveformdis - play in Fig.5.18 shows how the signal Comparator In our second circuit we’ll inves - - ‘compares’ two input voltages and Theinvertinginputisasimplepoten - tial divider that sets the voltage to half of the supply voltage, in this case 5V. The non-inverting input is connected to a potentiometer; effectively a vari - ablepotentialdivider.Thisallowsusto control the voltage to this input. In practical circuits this might be replaced with a potential divider in - volving a resistive input device, such as a light dependent resistor (LDR) or thermistor(we’llbelookingatacircuit usinganLDRnext).Somecircuitseven use two variable inputs to be com - pared – for example a line following robot might compare the inputs from two LDRs to determine its orientation on a line. Enter the comparator circuit shown in Fig.5.19 and experiment with the circuit by changing the potentiometer and observing the input/output volt - or ‘voltage level’ views to analyse the operation of the circuit. By changing thepotentiometeryouarechangingthe voltageatthenon-invertinginput.The inverting input is held at a constant voltage of about 5V. When the non-inverting input volt - age is higher than the inverting input, - back resistors the gain is very large, andthereforetheoutputswingstothe maximumvoltagepossible;thesupply F IN Voltage gain R R = − Fig.5.18. Waveform graph produced by the modi - is shown in blue and the output in red Fig.5.19.Asimplecircuittodemonstrate comparator

714. 56 Everyday Practical Electronics, March 2011 Teach-In 2011 VOLTAGE #URRENT ÛOWS FROM THE OPERA- TIONAL AMPLIÚER THROUGH THE BI COLOUR ,%$ $ TO GROUND 6

715. LIGHTING IT RED TO DEMONSTRATE A POSITIVE OUTPUT #ON- VERSELY

716. WHEN THE NON INVERTING INPUT IS LESS THAN THAT OF THE INVERTING INPUT

717. THE AMPLIÚER AMPLIÚES THE NEGATIVE INPUT BY A LARGE AMOUNT

718. RESULTING IN AN OUTPUT AT THE NEGATIVE SUPPLY AND HENCE LIGHTING THE GREEN ,%$ .OTICE THAT DESPITE WHAT YOU MAY HAVE THOUGHT

719. IT IS PRACTICALLY IMPOS- SIBLE TO GET AN EXACT 6 OUTPUT 4HIS WOULD

720. THEORETICALLY

721. BE POSSIBLE IF WE CAN ENSURE THAT BOTH INPUTS WERE EXACTLY THE SAME (OWEVER

722. IN PRACTICE

723. IT IS NOT POSSIBLE TO BE THIS ACCURATE

724. AND THE LARGE GAIN AND TINY VARIATION RESULTS IN A FULL SWING EITHER TO FULLY POSITIVE OR NEGATIVE Auto Light Switch )N OUR ÚNAL CIRCUIT

725. WEmLL SEE A PRAC- TICAL APPLICATION OF THE COMPARATOR CIRCUIT WE PLAYED WITH ABOVE )N THIS CIRCUIT

726. WEmLL USE AN ,$2 TO MONITOR THE LIGHT LEVEL AND AUTOMATICALLY TURN ON A LAMP ,!

727. FOR EXAMPLE FOR AN AUTOMATIC LIGHT CIRCUIT %NTER AND SIMULATE THE CIRCUIT SHOWN IN IG AND OBSERVE ITS OPERATION Y ADJUSTING THE POTENTIOMETER WE CAN SET THE POINT AT WHICH THE LAMP TURNS ON )N PRACTICE

728. THIS WOULD BE HOW DARK IT IS WHEN YOU WOULD LIKE THE LIGHT TO TURN ON 9OU MAY BE WONDERING WHY USING AN OP AMP FOR THIS PURPOSE IS BETTER THAN USING A SIMPLE TRANSISTOR SWITCH The Circuit Wizard way Fig.5.20. An automatic light switch using a comparator circuit CIRCUIT Y USING AN OPERATIONAL AMPLI- ÚER

729. AS SOON AS WE HIT THE PRESET VOLTAGE THE NON INVERTING INPUT VOLTAGE THE OPERATIONAL AMPLIÚER WILL GREATLY AM- PLIFY THE INPUT AND IMMEDIATELY GIVE US THE FULL SUPPLY VOLTAGE (OWEVER

730. USING ONLY A TRANSISTOR SWITCH YOU TEND NOT TO GET A PRECISE ONOFF BECAUSE OFTEN THERE IS A PERIOD WHERE THE TRANSISTOR IS NOT COMPLETELY SATURATED !N OSCILLATOR CIRCUIT IS SIMPLY A CIRCUIT THAT PROVIDES AN OUTPUT SIGNAL WITHOUT NEEDING ANY INPUT APART FROM A POWER SUPPLY q OF COURSEØ IG SHOWS THE CIRCUIT OF A SIMPLE OSCILLATOR CIRCUIT BASED ON A SINGLE OPERATIONAL AMPLIÚER %NTER THE CIRCUIT IN #IRCUIT 7IZARD

731. INVESTIGATE THE OUTPUT THAT IT PRODUCES AND THEN SEE IF YOU CAN EXPLAIN HOW THE CIRCUIT WORKS Hint: 9OU MIGHT NEED TO RECALL EAR- LIER WORK THAT YOU DID ON C-R CHARGING AND DISCHARGING CIRCUITS AND COMBINE THIS WITH WHAT YOU NOW KNOW ABOUT OPERATIONAL AMPLIÚER COMPARATORS 9OU WILL ÚND THAT #IRCUIT 7IZARD WILL DO A GREAT JOB OF SIMULATING THE OSCILLATOR CIRCUIT (OWEVER

732. BECAUSE THEREmS A LOT GOING ON IN A SHORT AMOUNT OF TIME

733. IT CANmT DO IT IN REAL TIME )F YOU TRY AT FULL SPEED YOUmLL MOST LIKELY GET VERY CONFUSING RESULTS 4O lSLOW THINGS DOWNm YOU CAN REDUCE THE SPEED OF SIMULATION BY CLICKING ON l4IMEm ON THE GREY BAR AT THE BOTTOM OF THE #IRCUIT 7IZARD WINDOW MS SHOULD WORK NICELY WITH MOST COMPUTERS Investigate 'JH O PQFSBUJPOBM BNQMJÜFS CFJOH VTFE JO BO an oscillator circuit Fig.5.22(right). Changing simulation TQFFE JO $JSDVJU 8J[BSE

734. Everyday Practical Electronics, March 2011 57 Teach-In 2011 If your computer is a bit on the slow side, opt for less until you get a nice looking trace (see Fig.5.22). You will also need to adjust the scale on your graph; Fig.5.23 shows some suggested values that will give you a graph like that shown in Fig.5.24. The rest is for you to investigate… so how does it do it? The blue trace/probe in Fig. 5.24 should give you some clues! Fig.5.23(above). Suggested graph parameters Fig.5.24(right). Typical waveforms produced by the oscillator circuit Amaze AnswerstoQuestions 5.1. See Fig.5.3 5.2. See Fig.5.5 5.3. See page 51 5.4. 200 5.5. 100,000 5.6. See Fig.5.7(a) 5.7. See Fig.5.8 with R1 = 5k:, R2 = 75k:, C1 = 1.59μF, C2 = 212pF Before we could use transistors in electronic circuits, we had to use valves. These looked a bit like light bulbs. They needed lots of space, lots of power and often produced a lot of heat (they had to be heated up inter- nally before they could work). This made designing simple circuits quite complicated – not only did we need a low-voltage high-current heater supply, but we also needed a high voltage supply of around 200V or more. When transistors came along, they revolutionised electronics, making it possible to have small, complex circuits that operated from low voltage. Today, we can make transistors so TINY THAT WE CAN ÚT LITERALLY MILLIONS of them on an area the size of your SMALL ÚNGER Thecurrentgenerationofmicroproc- essorsaremanufacturedusingaprocess that’s capable of producing individual transistors 1,000 times smaller than the diameter of a human hair. That means that the in- d i v i d u a l semiconductor lay- ers might only have a few tens or hundreds of atoms. In fact, the latest technology is capable of producing transistors that are less than 25nm across – that’s a mere 0.000025mm! Next month! In next month’s Teach-In we will be investigating logic circuits. Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofﬁce of EPE – see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com). Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developeralsooffersanevaluationcopy of the software that will operate for 30 days,althoughitdoeshavesomelimita- tions applied, such as only being able tosimulatetheincludedsamplecircuits and no ability to save your creations. Fig.5.25. Valves from the 1940s and 1950s com- paredwithtransistorsfromthe1960sand1970s Fig.5.26. This 1970s semiconductor memory device contains the equivalent of more than 65,000 individual transistors. The latest chips have more than 100 million devices in the same space!

735. 44 Everyday Practical Electronics, April 2011 Teach-In 2011 By Mike and Richard Tooley Part 6: Logic circuits Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS Digital logic Logic circuits are the basic building blocks of digital circuits and systems. Logic circuits have inputs and outputs that can only exist in one of two discrete states, variously known as ‘on’ and ‘off’, ‘high’ and ‘low’, or ‘1’ and ‘0’. Logic circuits usually have several inputs and one or more outputs. At any instant of time, the state of the inputs will determine the state of the output, according to the logic function provided by the circuit. If this is beginning to sound a little complicated, let’s look at a couple of simple logic functions that can be I N THIS instalment of Teach-In we introduce the basic building blocks of digital circuits. We explain the operation of each of the most common types of logic gate and show how they can be combined together in order to solve more complex logic problems. We also introduce bistable circuits and show how they can be used to remember a momentary event. We shall be using Circuit Wizard to investigate each of the basic logic gates before moving on to explore some applications. Finally, in Amaze we look at how recent advances in technology have provided us with digital circuits that are capable of operation at speeds that are increasingly fast. couple of switches and a lamp and battery. Consider the circuit shown in Fig.6.1. In this circuit, a battery is connected to a lamp via two switches, A and B. It should be obvious that the lamp will only operate when both of the switches are closed (ie, both A AND B are closed). Let’s look at the operation of the circuit in a little more detail. Since there are two switches (A and B) and there are two possible states for each switch (open or closed), there is a total of four possible conditions for the circuit. We have summarised these states in Fig.6.2. Note that the two states (ie, open or closed) are mutually exclusive Learn

736. Everyday Practical Electronics, April 2011 45 Teach-In 2011 and that the switches cannot exist in any other state than completely open or completely closed. Because of this, we can represent the state of the switches using the binary digits, 0 and 1, where an open switch is represented by 0 and a closed switch by a 1. Furthermore, if we assume that ‘no light’ is represented by a 0 and ‘light on’ is represented by a 1, we can rewrite Fig.6.2 in the form of a truth table, as shown in Fig.6.3. Another circuit with two switches is shown in Fig.6.4. This circuit differs from that shown in Fig.6.1 by virtue of the fact that the two switches are connected in parallel rather than in series. In this case, the lamp will operate when either of the two switches is closed (in other words, when A OR B is closed). As before, there is a total of four possible conditions for the circuit. We can summarise these conditions in Fig.6.5. Once again, adopting the convention that an open switch can be represented by 0 and a closed switch by 1, we can rewrite the truth table in terms of the binary states, as shown in Fig.6.6. The basic logic functions can be combined to produce circuits that satisfy a more complex logical operation. For example, Fig.6.7 shows a simple switching circuit in which the lamp will operate when switch A AND either switch B OR switch C is closed. The truth table for this arrangement is shown in Fig.6.8. Logic gates Logic gates are building blocks that are designed to produce the basic logic functions, AND, OR, NOT, etc. These circuits are designed to be interconnected into larger, more complex, logic circuit arrangements. Each gate type has its own symbol and we have shown both the Brit- ish Standard (BS) symbol together with the more universally accepted American Standard (MIL/ANSI) symbol. Note that, while inverters and buffers each have only one input, exclusive-OR gates have two inputs and the other basic gates Fig.6.1. AND switch and lamp logic Fig.6.4. OR switch and lamp logic Fig.6.2. Possible states for the circuit of Fig.6.1 Fig.6.5. Possible states for the circuit of Fig. 6.4 Fig.6.3 (right). Truth table for the AND switch and lamp logic Fig.6.6 (right). Truth table for the OR switch and lamp logic Fig.6.7. Simple switching circuit using AND and OR logic Fig.6.8 (right). Truth table for the simple switching circuit shown in Fig.6.7

737. 46 Everyday Practical Electronics, April 2011 Teach-In 2011 Buffers Buffers do not affect the logical state of a digital signal (ie, a logic 1 input results in a logic 1 output, and a logic 0 input results in a logic 0 output). Buffers are normally used to provide extra current drive at the output, but can also be used to regu- larise the logic levels present at an interface. The Boolean expression for the output, Y, of a buffer with an input, X, is Y = X. (eg, AND, OR, NAND and NOR) are commonly available with up to eight inputs. Some of the logic gates shown in Fig.6.9 have inverted outputs. These gates are the NOT, NAND, NOR, and Exclusive-NOR and the small circle at the output of the gate (see Fig.6.10a) indicates this inversion. It is important to note that the output of an inverted gate (eg, NOR) is identical to that of the same (ie, non-inverted) function with its output connected to an inverter (or NOT gate) as shown in Fig.6.10b). The logical function of a logic gate can also be described using Boolean notation. In this type of notation, the OR function is represented by a ‘+’ sign, and the NOT function by an overscore or ‘/’. Thus the output, Y, of an OR gate with inputs A and B can be represented by the Boolean algebraic expression: Y = A + B Similarly, the output of an AND gate can be shown as: the logic functions of each of the basic logic gates that we met earlier in Fig.6.9: Fig.6.9. Logic gate symbols and truth tables Fig.6.10. Logic gates with inverted outputs Fig.6.11 (above). Majority vote logic circuit Fig.6.12 (right). Truth table for the majority vote logic circuit

738. Everyday Practical Electronics, April 2011 47 Teach-In 2011 Inverters Inverters are used to complement the logical state (ie, a logic 1 input results in a logic 0 output and vice versa). Inverters also provide extra current drive and, like buffers, are used in interfacing applications where they provide a means of regularising logic levels present at the input or output of a digital system. The Boolean expression for the output, Y, of an inverter with an input, X, is Y = /X. AND gates AND gates will only produce a logic 1 output when all inputs are simultaneously at logic 1. Any other input combination results in a logic 0 output. The Boolean expression for the output, Y, of an AND gate OR gates OR gates will produce a logic 1 output whenever any one, or more inputs are at logic 1. Putting this another way, an OR gate will only produce a logic 0 output whenever all of its inputs are simultaneously at logic 0. The Boolean expression for the output, Y, of an OR gate with inputs, A and B, is Y = A + B. NAND gates NAND (ie, NOT-AND) gates will only produce a logic 0 output when all inputs are simultaneously at logic 1. Any other input combination will produce a logic 1 output. A NAND gate, therefore, is nothing more than an AND gate with its output inverted! The circle shown at the output denotes this inversion. The Boolean expression for the output, Y, of a NAND gate with inputs, NOR gates NOR (ie, NOT-OR) gates will only produce a logic 1 output when all inputs are simultaneously at logic 0. Any other input combination will produce a logic 0 output. A NOR gate, therefore, is simply an OR gate with its output inverted. A circle is again used to indicate inversion. The Boolean expression for the output, Y, of a NOR gate with inputs, A and B, is Y = A + B. Exclusive-OR gates Exclusive-OR gates will produce a logic 1 output whenever either one of the two inputs is at logic 1 and the other is at logic 0. Exclusive- OR gates produce a logic 0 output whenever both inputs have the same logical state (ie, when both are at logic 0 or both are at logic 1). The Boolean expression for the output, Y, of an exclusive-OR gate Exclusive-NOR gates Exclusive-NOR gates will produce a logic 0 output whenever either one of the two inputs is at logic 1 and the other is at logic 0. Exclusive- NOR gates produce a logic 1 output whenever both inputs have the same logical state (ie, when both are at logic 0 or both are at logic 1). The Boolean expression for the output, Y, of an exclusive-NOR gate with inputs, A and B, is Combinational logic The basic logic gates can be com- binedtogethertosolvemorecomplex logicfunctions.Thisismadepossible by adopting a standard range of logic levels(ie,voltagelevelsusedtorepre- sent the logic 1 and logic 0 states) so that the output of one logic circuit is compatible with the input of another. As an example, let’s assume that we require a logic circuit that will produce a logic 1 output whenever two, or more, of its three inputs are at logic 1. This circuit (shown in Fig.6.11) is often referred to as a majority vote circuit, and its truth table is shown in Fig.6.12. Note that the outputs of the three two-input AND gates are fed to the three inputs of the OR gate, and that the output of the OR gate will become logic 1 whenever any one or more of the two-input AND gates detects a condition in which two of the inputs are simultaneously at logic 1. As a further example, consider how we might combine several of the basic logic gates (AND, OR and NOT) in order to realise the exclusive-OR function. In order to solve this problem, consider the Boolean expression for the exclusive-OR function that we met earlier: /A and /B can be obtained by simply inverting A and B respec- be obtained using two two-input AND gates. Finally, these two can be applied to a two-input OR gate in order to obtain the required The complete solution is shown in Fig.6.13. Fig.6.13. An exclusive-OR gate produced from AND, OR and NOT gates

739. 48 Everyday Practical Electronics, April 2011 Teach-In 2011 Bistables Bistable circuits provide us with a means of remembering a transient logic condition. For example, the logic that controls a lift must remember that the lift has been called in response to a push-button that only requires momentary operation. As its name suggests, the output of a bistable (or ) circuit has two stables states (logic 0 or logic 1). Once set, the output of a bistable will remain at logic 1 or logic the bistable is reset. A bistable thus forms a simple form of memory, remaining in its latched state (either set or reset) until a signal is applied to it to change its state (or until the supply is disconnected). The simplest form of bistable is the R-S bistable. This device has two inputs, SET and RESET, and complementary outputs, Q and Q. A logic 1 applied to the SET input will cause the Q output to become (or remain at) logic 1, while a logic 1 applied to the RESET input will cause the Q output Two simple forms of R-S bistable based on cross-coupled logic gates are shown in Fig.6.14. Fig.6.14(a) is based ontwocross-coupledtwo-inputNAND gates,whileFig.6.14(b)isbasedontwo cross-coupled two-input NOR gates. D-type bistable Unfortunately,thesimplecross-coupled logic gate bistable has a number ofseriousshortcomings(considerwhat wouldhappenifalogic1wassimulta- neously present on both the SET and RESET inputs!) and practical forms of bistable make use of much improved purpose-designed logic circuits, such as D-type and J-K bistables. The D-type bistable has two inputs: D (standing variously for data or de lay)andCLOCK(CLK).Thedatainput (logic 0 or logic 1) is clocked into the bistablesuchthattheoutputstateonly changeswhentheclockchangesstate. Operation is thus said to be synchronous. Additional subsidiary inputs (which are invariably active low) are provided, which can be used to directly set or reset the bistable. These are usually called PRESET (PR) and CLEAR (CLR). D-type bistables are used both as latches (a simple form of memory) and as binary dividers. The simple circuit arrangement in Fig.6.15, together with the timing diagram shown in Fig. 6.16 illustrate the operation of D-type bistables. to become (or remain at) logic 0. In either case, the bistable will remain in its SET or RESET state until an input is applied in such a sense as to change the state. Note also that the Q and Q outputs always have opposite logical states. Thus, when the Q output is at logic 1 the Q output will be at logic 0, and versa.

740. Everyday Practical Electronics, April 2011 49 Teach-In 2011 J-K bistables J-K bistables (see Fig.6.17) have two clocked inputs (J and K), two direct inputs (PRESET and CLEAR), a CLOCK (CK) input, and outputs (Q and Q). As with R-S bistables, the two outputs are complementary (ie, when one is 0 the other is 1, and vice versa). Similarly, the PRESET and CLEAR inputs are invariably both active low (ie, a 0 on the PRESET input will set the Q output to 1, whereas a 0 on the CLEAR input will set the Q output to 0). Fig.6.18 summarises the input and corresponding output states of a J-K bistable for various input states. J-K bistables are the most so- dividers, shift registers, and latches. The circuit arrangement of a four-stage binary counter, based on J-K bistables, is shown in Fig.6.19. The timing diagram for this circuit is shown in Fig.6.20. Each stage successively divides the clock input signal by a factor of two. Note that a logic 1 input is transferred to the respective Q-output on the falling edge of the clock pulse, and all J and K inputs must be taken to logic 1 to enable binary counting. Practical logic circuits You should now have a basic grasp of the theory of logic circuits, but what we haven’t done yet is give you an idea of what these devices look like and how they appear in practical logic circuits. So, let’s end this month’s Learn Fig.6.19. Circuit for a four-stage binary counter using J-K bistables Fig.6.20. Timing diagram for the four-stage binary counter of Fig.6.19 Fig.6.18. J-K bistable operation (ie, Q is reset (ie, Q is reset (ie, Q is reset (ie, Q is reset whatever state it was before, while

741. 50 Everyday Practical Electronics, April 2011 Teach-In 2011 The 4013 dual D-type bistable is supplied in various packages, including the dual-in-line (DIL) package shown in Fig.6.21. This device uses standard complementary metal oxide semiconductor (CMOS) technology, and its pin connections are shown in Fig.6.22. Note that pin 14 and pin 7 supply power to both of the D-type bistables. The 74F08 quad two-input NAND gate is also available in several different packages. We have shown the small integrated circuit (SOIC) package in Fig.6.23. This package is ideal for surface mounting rather than through-hole mounting used with the DIL package that we met before. The 74F08 contains four independent NAND gates and uses ‘fast’ transistor- transistor logic (TTL). The pin connection diagram for the chip is shown in Fig.6.24. As with the 4013, the supply connections (pin 14 and pin 7) are common to all four of the internal logic gates. Please note! Some logic devices, particularly CMOS types, are static-sensitive and special precautions are needed when handling and transporting them. Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofﬁce of EPE – see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com). Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developeralsooffersanevaluationcopy of the software that will operate for 30 days,althoughitdoeshavesomelimita- tions applied, such as only being able tosimulatetheincludedsamplecircuits and no ability to save your creations. Fig.6.21. A 4013 dual D-type bistable in a plastic dual-in-line (DIL) package. This chip was manufactured in 1992 Fig.6.23. A 74F08 quad two-input NAND gate in a small surface-mount package (SOIC). This chip was manufactured in 2001 Fig.6.22. Pin connections for the 4013 dual D-type bistable IC Fig.6.24. Pin connections for the 74F08 quad two-input NAND gate IC Check – How do you think you are doing? 6.1. Identify each of the logic symbols shown in Fig.6.25 6.2. Draw the truth table for the logic gate arrangement shown in Fig. 6.26. 6.3. Show how three two-input ANDgatescanbeconnectedtogeth- er to form a four-input AND gate. Fig.6.25. See Question 1 Fig.6.26. See Question 2 6.4. State the Boolean logic expression for the output of each of the gate arrangements shown in Fig.6.27 – opposite. 6.5. Devise a logic gate arrangement that provides an output d e s c r i b e d by the truth table shown in Fig.6.28. Fig.6.28. See Question 5

742. Everyday Practical Electronics, April 2011 51 Teach-In 2011 Fig.6.27. See Question 4 Build – The Circuit Wizard way YOU’VE learnt the theory about logic gates, so now let’s try it out using Circuit Wizard. Anyone who’s experimented or prototyped with discrete logic circuits before will be all too familiar with hope- lessly prodding a logic probe into an incomprehensible ‘rat’s nest’ of breadboard and link wires. Fortunately, nowadays we can do all this and more using software packages before we commit any copper to PCB. Circuit Wizard really does have a few aces up its sleeve when it comes to working with logic. First, you can work directly with the logic gates themselves and let it worry about the chip packages (see later on), as well as a number of dedicated inputs/outputs and simulation schemes that bring the circuits to life and visually convey what’s really going on in the circuit. In this instalment of Build we’ll be trying out some logic gates to see how they operate, as well as experimenting with some real life applications. Opening the gates Circuit Wizard includes a large range of logic devices in both CMOS and TTL versions (note that the extent of the logic devices may depend on the Gate numbers When you add a gate to the drawing area you should notice that it will automatically number your gate in accordance with the corresponding IC required. As each IC contains a number of gates, an the chip reference (eg, IC1a) to show which has been allocated. Once the total number of gates has exceeded that of the IC, Circuit Wizard will automatically include a new chip, and so on. You are able to change which gate has been allocated within the chip. This can be useful when it comes to generating the However, the automatic allocation works great for most users. Circuit Wiz- ard will also add powerFig.6.29. Changing logic families for a logic gate connections ‘in the background’, so that these are accounted for in net lists when moving on to PCB generation. The best way to understand the operation of the basic gates is to drop one on to the drawing area, add inputs and outputs and see how the output changes in response to changes in the inputs. Circuit Wizard has some really useful input toggles and output indicators which can be found at the top of the ‘Logic Gates’ folder (see Fig.6.30). Switching to the ‘Logic View’ (click on the vertical tab on the left of the drawing area) is a particularly useful way to analyse any logic version of Circuit Wizard that you are running). The first thing that you may notice is that in the Gallery (right-hand panel) you can access standard and Schmitt varie- ties of gates in the ‘Logic Gates’ folder, as well as each family of chip separately in the ‘Integrated Circuits’ folder. We can only assume that this is for the purpose of providing quick access to the more common gates. By default, 4000 series ICs will be used. However, you are able to select the family of gate by selecting the appropriate model in the properties context box; see Fig. 6.29 (double-click the component to access this). This default behaviour can also be altered in the software’s setting if required. Fig.6.30. A simple arrangement to test an AND gate

743. 52 Everyday Practical Electronics, April 2011 Teach-In 2011 Build – The Circuit Wizard way Logic circuits usually contain a number of different gates and can get very complicated. De- the simplest arrangement of gates to perform the logical function that’s required. However, with the widespread use and avail- ability of microprocessors, complex combinational logic circuits are becoming a thing of the past. Have a go at entering and testing the logic circuit shown in Fig.6.32, and produce a truth table. Could the function of this circuit have been reproduced with fewer gates? If you think about actually producing the circuit above you would need three logic ICs and two of the ICs would only have one gate used in to do things. Fortunately, logic designers came up with a great idea; what if we could use just a single gate and wire them in such a way to act like the other gates? In this way, you would only need to buy one type of IC. It turns out that the NAND gate is the ideal candidate for this as you can produce all of the other gates using them – we call them ‘NAND equivalents’. Fig.6.33 shows the NAND equivalent for an AND gate. Enter the circuit in to Circuit Wizard and verify that the combination acts just like an AND gate. In this case, the first gate is a straight forward NAND and the second circuit. This view uses both colour coding as well as 1s and 0s at the inputs/outputs of each pin to show the logic state. This can really help you see what’s going on around the circuit. One important thing to note about the logic indicators and the ‘Logic Level’ view is that the logic high state is indicated by red, and the logic low by green. This might seem a little counter- intuitive to some people – the author included! Give it a try Experiment with some of the basic gates; AND, OR, NAND, XOR and NOT. Draw up a truth table for each gate and check that this matches what you’ve seen in Learn. Alternatively, we’ve developed an interactive logic gate worksheet (see Fig.6.31). This can be downloaded from the Teach-In 2011 website; www.tooley.co.uk/teach-in – follow the link to Circuit Wizard downloads. Print out the worksheet and complete the truth tables by simulating them on screen. gate acts as a NOT gate. Hence, the result is ‘NOT NAND’ or AND. for the other gates. You can also download our NAND Gate Equivalent simulator (Fig.6.34) from the Teach-In website, which includes a number of other equivalents for you to explore. Fig.6.31. A view of our logic gate worksheet, which can be downloaded from: www.tooley.co.uk/teach-in Fig.6.32. A combinational logic circuit Fig.6.33. An AND gate made using NAND gates (in other words, a ‘NAND equivalent’ of an AND gate

744. Everyday Practical Electronics, April 2011 53 Teach-In 2011 Fig.6.33. Download our NAND gate equivalent simulator from: www. tooley.co.uk/teach-in Intruder alarm Now we’ll look at a real-life application of a simple logic circuit. Fig.6.35 shows an intruder alarm circuit. When any one of the links (simulated by push-to-break buttons) is broken, the alarm is activated. Enter the circuit and try it out for yourself! Advanced readers might like to see if they can adapt the circuit to latch the alarm on once a link has been broken. Ripple counter Another area of logic design is sometimes described as sequential logic. Often this involves counting and/or timing. Fig.6.36 shows what is commonly known as a ripple counter or cascade counter. It produces a binary count using a series of J-K bistables or ‘flip-flops’. Enter the circuit and look closely at its operation. The ‘Logic View’ is excellent for this kind of circuit, and you should be able to see how the logic high ‘ripples’ along the flip-flops in order to generate a four-bit binary counting sequence. Fig.6.35.Intruderalarmcircuit.Whenoneofthe‘links’isbroken,thealarmsounds Fig.6.36. Four-bit ripple counter using J-K bistables The world’s fastest microprocessor resulted from an investment of $1.5 billion, and operates at a speed of 5.2GHz (courtesy of International Business Machines Corp.)

745. 54 Everyday Practical Electronics, April 2011 Teach-In 2011 Decade counter A binary count could be really useful for lots of applications. Apart from possibly a few computer nerds, not all that many people can easily read a binary number! Therefore, if we need to display a number to a consumer we need to convert this to a display- able number. This can be easily achieved with a 74LS47 seven- segment display decoder, a driver chip and a seven-segment LED display (common anode). The chip decodes the four- bit lines of the binary count and outputs a number on the seven-segment LED display by turning on/off the appropriate Build – The Circuit Wizard way Fig.6.37. A decade (ie, 0-9) counter circuit using J-K bistables and a seven- segment display lines. Amend your ripple counter circuit as shown in Fig.6.37. The NAND gate is used to reset the flip-flops when the count reaches 9, the highest single-digit number that can be displayed. A block schematic diagram of a logic system used in a large aircraft is shown in Fig.6.38. Investigate The system is designed to alert - ible and audible warnings that one or more of the aircraft’s undercar- riage doors remain open when the logic 1 signals when the respective door is open and logic 0 when closed. All of the warning indicators are ‘active low’ and require a logic 0 to produce a visible or audible output. Study the circuit carefully and then see if you can answer each of the following questions: 1. What logic level appears at points X, Y and Z with all of the doors closed? 2. What logic level appears at points X, Y and Z with the left wing door open and all other doors closed? 3. What logic level appears at points X, Y and Z with the nose door open and all other doors closed? 4. When any one or more of the doors opens, the audible warningFig.6.38. A block schematic of a logic system used in an aircraft

746. Everyday Practical Electronics, April 2011 55 Teach-In 2011 should sound and remain operat- the alarm by means of the RESET Answers to Check questions 6.1. (a) Three input OR gate 2. See Fig. 6.40 3. See Fig. 6.41 5. See Fig. 6.42 - - - around 100 times faster than this. Next month! Teach-In generators. Fig.6.40. Answer to Question 2 Fig.6.41. Answer to Question 3 Fig.6.42. Answer to Question 5 Amaze signal to travel from the input(s) of a output is usually extremely small (ps). This time (often referred to as propagation delay) has a major im- Fig.6.39. IBM’s new zEnterprise Sys- tem mainframe (courtesy of International Business Machines Corporation) By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! CIRCUIT WIZARDCircuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT See Direct Book Service – pages 75-77 in this issue * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export

747. 44 Everyday Practical Electronics, May 2011 Teach-In 2011 By Mike and Richard Tooley Part 7: Timer circuits Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS we measure time with a very high degree of accuracy. I N THIS instalment of Teach-In, we will bring together several important ideas and concepts that we’ve already met in the earlier parts. At the same time, we will introduce you to a highly versatile integrated circuit (IC), the 555 timer. Using this IC, we will show you how you can quickly and easily design circuits that will produce time delays from a few hundred nanoseconds to several hundred seconds, and square wave pulses of known frequency, period and duty cycle. Build and Investigate will extend this further with a detailed look at some practical timer and pulse generator circuits. Finally, in Amaze we look at ways in which To begin to understand how timer circuits operate, it is worth spending a few moments studying the internal circuitry of the 555 timer, see Fig.7.2. Essentially, the chip comprises two operational ampli- with an R-S bistable. In addition, incorporated so that an appreciable current can be delivered to a load. Learn The 555 timer The 555 timer is, without doubt, one of the most versatile integrated circuit chips ever produced. Not only is it a neat mixture of analogue and digital circuitry, but its applications are virtually limitless in the world of digital pulse generation. The chip also makes an excellent case study for beginners because it brings together a number of important concepts and techniques. The standard 555 timer is supplied in a standard 8-pin dual-in-line (DIL) package with the pinout shown in Fig.7.1. Fig.7.1. Pinout connections for a standard 555 timer IC

748. Everyday Practical Electronics, May 2011 45 Teach-In 2011 Sinking and sourcing Unlike the standard logic devices that we met last month, the 555 timer can both sink and source current. It’s worth taking a little time to explain what we mean by these two terms: When sourcing current, the 555’s output (pin 3) is in the high state, out of the output pin into the load and down to 0V, as shown in Fig.7.3(a). When sinking current, the 555’s output (pin 3) is in the low state, in the positive supply (+Vcc) through the load and into the output (pin 3), as shown in Fig.7.3(b). Returning to Fig.7.2, the single transistor switch, TR1, is provided as a means of rapidly discharging an external timing capacitor. Because the series chain of resistors, comprising R1, R2 and R3, all have identical values, the supply voltage (VCC) is divided equally across the three resistors. The voltage at the non- inverting input of IC1 is one-third of the supply voltage (VCC), while that at the inverting input of IC2 is two-thirds of the supply voltage (VCC). Thus, if VCC is 9V, 3V will appear across each resistor and the upper comparator will have 6V applied to its inverting input, while the lower comparator will have 3V at its non-inverting input. The 555 family The standard 555 timer is housed in an 8-pin DIL packageandoperatesfrom supply rail voltages of between 4.5V and 15V. This, of course, encompasses Feature Function A A potential divider comprising R1, R2 and R3 connected in series. Since all three resistors have the same values the input voltage (VCC) will be divided into thirds, i.e. one third of VCC will appear at the junction of R2 and R3 while two thirds of VCC will appear at the junction of R1 and R2. B Two operational amplifiers connected as comparators. The operational amplifiers are used to examine the voltages at the threshold and trigger inputs and compare these with the fixed voltages from the potential divider (two thirds and one third of VCC respectively). C An R-S bistable stage. This stage can be either set or reset depending upon the output from the comparator stage. An external reset input is also provided. D An open-collector transistor switch. This stage is used to discharge an external capacitor by effectively shorting it out whenever the base of the transistor is driven positive. E An inverting power amplifier. This stage is capable of sourcing and sinking enough current (well over 100mA in the case of a standard 555 device) to drive a small relay or another low-resistance load connected to the output. Table 7.1: Main features of the 555 timer IC Fig.7.2. Internal schematic arrangement of the standard 555 timer Fig.7.3. Loads connected to the output of a 555 timer: (a) current sourced by the timer when the output is high, (b) current sunk by the timer when the output is low

749. 46 Everyday Practical Electronics, May 2011 Teach-In 2011 goes low. The device then remains in the inactive state until another falling trigger pulse is received. Output waveform The output waveform produced by the circuit of Fig.7.4 is shown in Fig.7.5. The waveform has the following properties: Time for which output is high: the normal range for TTL devices (5V ±5%) and thus the device is ideally suited for use with TTL circuitry. Thefollowingversionsofthestand- ard555timerarecommonlyavailable: Low power 555 The low power 555 timer is a CMOS version that is both pin and function compatible with its standard counterpart. By virtue of its CMOS technology, the device operates over a somewhat wider range of supply voltages (2V to 18V) and consumes minimal operating current (120 A typical for an 18V supply). Notethat,byvirtueofthelow-power CMOS technology employed, the device does not have the same output current drive as that possessed by its standardcounterparts.However,itcan supply up to two standard TTL loads. 556 dual timer The 556 is a dual version of the standard 555 timer housed in a 14- pin DIL package. The two devices may be used entirely independently and share the same electrical characteristics as the standard 555. Low power 556 The low power 556 is a dual version of the low power CMOS 555 timer contained in a 14-pin DIL package. The two devices may again be used entirely independently and share the same electrical characteristics as the low power CMOS 555. Please note! Low power timers use CMOS technology and should be handled using anti-static precautions. Monostable pulse generator Fig. 7.4 shows a standard 555 timer operating as a monostable pulse generator. The term ‘monostable’ refers to the fact that the output has only one stable state, and it will always return to this state after a period of time spent in the opposite state. The monostable timing period (ie, the time for which the output is high) is initiated by a falling edge trigger pulse applied to the trigger input (pin 2). When this falling edge trigger pulse is received and falls below one third of the supply voltage, the output of IC2 goes high and the bistable will be placed in the set state. The inverted Q output (ie, Q) of the bistable then goes low, the internal transistor TR1 is placed in the off (non-conducting) state and the output voltage (pin 3) goes high. The capacitor, C, then charges through the series resistor, R, until the voltage at the threshold input reaches two thirds of the supply voltage (Vcc). At this point, the output of the upper comparator changes state and the bistable is reset. The inverted Q output (ie, Q) then goes high, TR1 is driven into Fig.7.5. Waveforms for monostable operation ton = 1.1 C R Recommended trigger pulse width: on tr t t 4 Where ton and ttr are in seconds, C is in farads and R is in ohms. The period of the 555 monostable output can be changed very easily by simply altering the values of the timing resistor, R, and/or timing capacitor, C. Doubling the value of R will double the timing period. Similarly, doubling the value of C will double the timing period. Please note! The usual range of values for capacitance and resistance in a monostable timer are 470pF to 470 F and 1k to 3.3M respectively. Outside this range operation is less predictable. Example 1 Now let’s work through a simple design example. For this we shall

750. Everyday Practical Electronics, May 2011 47 Teach-In 2011 assume that we need a circuit that will produce a 10ms pulse when a negative-going trigger pulse is applied to it. Using the circuit shown in Fig. 7.4, the value of monostable timing period can be calculated from the formula: From which: in order to avoid making the value of R too high. A value of 100 F should be appropriate and should also be easy to obtain. Making R the subject of the formula, and substituting for C = 100 F gives: ton = 1.1 C R We need to choose an appropriate value for C that is in the range stated earlier. Since we require a fairly modest time period, we will choose a mid-range value for C. This should help to ensure that the value of R is neither too small nor too large. A value of 100nF should be appropriate and should also be easy to obtain. Making R the subject of the formula and substituting for C = 100nF gives: 6 610 R = ×10 = 0.091×10 110 or 9.1 k Alternatively, the graph shown in Fig.7.6 can be used. Example 2 Next, we shall design a timer circuit that will produce a +5V output for a period of 60s when a ‘start’ button is operated. The time period is to be aborted when a ‘stop’ button is operated. For the purposes of this example we shall assume that the ‘start’ and ‘stop’ buttons both have normally-open (NO) actions. The value of monostable timing period can be calculated from the formula: ton = 1.1 C R We need to choose an appropriate value for C that is in the range stated earlier. Since we require a fairly long time period we will choose a relatively large value of C ont 60s 60 R = = = 1.1C 1.1×100 F -6 60 = 110×10 From which: In practice 560k (the nearest preferred value) would be adequate. The ‘start’ button needs to be connected between pin 2 and ground, while the ‘stop’ button needs to be connected between pin 4 and ground. Each of the inputs requires Fig.7.7 (above). Circuit diagram for a 60 second timer (see Example 2) Fig.7.6. (left) Graph for determining values of C, ton and R for a 555 operating in monostable mode. The red line shows how a 10ms pulse will be produced when C = 100nF and R = 91k (see Example 1) ont 10 ms R = = = 1.1C 1.1×100 nF -3 -9 10×10 = 110×10 ms nF k 6 660 R = ×10 = 0.545×10 110 or 545 kk 1

751. 48 Everyday Practical Electronics, May 2011 Teach-In 2011 a ‘pull-up’ resistor to ensure that the input is taken high when the switch is not being operated. The precise value of the ‘pull-up’ resistor is unimportant, and a value of 10k will be perfectly adequate in this application. The complete circuit of the 60s timer is shown in Fig.7.7. Astable pulse generator How the standard 555 can be con- astable pulse generator, is shown in Fig.7.8. In order to understand how this circuit operates, assume that the output (pin 3) is initially high and that TR1 is in the non-conducting state. The capacitor, C, will begin to charge with current supplied by series resistors, R1 and R2. Time for which output is low:When the voltage at the threshold input (pin 6) exceeds two thirds of the supply voltage, the output of the upper comparator, IC1, will change state and the bistable will become reset, due to the voltage transition that appears at R. This, in turn, will make the Q output go high, turning TR1 on and saturating it at the same time. Due to the inverting action of output (pin 3) will go low. The capacitor, C, will now dis- R2 into the collector of TR1. At a certain point, the voltage appearing at the trigger input (pin 2) will have fallen back to one third of the supply voltage, at which point the lower comparator will change state and the voltage transition at S (Fig.7.2) will return the bistable to its original set condition. The inverted Q output then goes low, TR1 switches off (no longer conducting), and the output (pin 3) goes high. Thereafter, the entire charge/discharge cycle is The output waveform produced by the circuit of Fig.7.8 is shown in Fig.7.9. The waveform has the following properties: Time for which output is high: 1 2 1.44 p.r.f. = C R +2R ton = 0.693 C (R1 + R2) Period of output waveform: toff = 0.693 C R2 Pulse repetition frequency: t = ton + toff = 0.693 C (R1 + 2R2) Fig.7.9. Waveforms for astable operation 2 for a 555 operating in astable mode 2 1 Mark-to-space ratio: on 1 2 off 2 t R +R = t R Duty cycle: on 1 2 on off 1 2 t R +R = ×100% t +t R +2R

752. Everyday Practical Electronics, May 2011 49 Teach-In 2011 Where t is in seconds, C is in farads, R1 and R2 are in ohms. When R1 = R2, the duty cycle of the astable output from the timer can be found by letting R = R1 = R2. In this condition: be a problem if we need to produce a precise square wave in which ton = toff. However, by making R2 very much larger than R1, the timer can be made to produce a reasonably symmetrical square wave output. (Note, that the minimum recommended value for R2 is 1k – see Please note!). If R2 R1, the expressions for p.r.f. and duty cycle simplify to: the formula, and substituting for C = 1 F gives: on 1 2 off 2 t R + R R+ R 2 = = = = 2 t R R 1 In this case, the duty cycle will be given by: on 1 2 on off 1 2 t R + R = ×100% = ×100% t + t R + 2R R + 2R R + R = ×100% R + 2R Thus: on on off t 2R 2 = ×100% t +t 3R 3 2 = ×100% = 67% 3 The p.r.f. of the 555 astable output can be changed very easily by simply altering the values of R1, R2, and C. The required values of C, R1 and R2 for any required p.r.f. and duty cycle can be determined from the formulae shown earlier. Alternatively, the graph shown in Fig.7.10 can be used when R1 and R2 are equal in value (corresponding to a 67% duty cycle). Please note! The usual range of values for capacitance and resistance in an astable timer are 10nF to 470 F for C, and 1k to 1M for R1 and R2. As for the monostable circuit, operation is less predictable outside this range. Square wave generators Because the high time (ton) is always greater than the low time (toff), the mark-to-space ratio produced by a 555 timer can never be made equal to (or less than) unity. This could 2 0.72 p.r.f. = CR on 2 on off 2 t R 100% t + t 2R 2 1 100% 50% 2 Example 3 Let’s design a pulse generator that will produce a p.r.f. of 10Hz with a 67% duty cycle (ie, the output will be high for one third of the time and low for two thirds of the time). Using the circuit that we met in Fig.7.8, the value of p.r.f. can be calculated from: 1 2 1.44 p.r.f. = C R +2R 67%, we can make R1 equal to R2. Hence, if R = R1 = R2 we obtain the following relationship: 1.44 1.44 0.48 p.r.f. = = = C R+2R 3CR CR We need to choose an appropriate value for C that is in the range stated earlier. Since we require a fairly low value of p.r.f., we will choose a value for C of 1 F. This should help to ensure that the value of R is neither too small nor too large. A value of 1 F should also be easy to obtain. Making R the subject of 0.48 R = = = p.r.f.×C -6 0.48 = p.r.f.×1×10 Hence: 3 3480×10 R = = 4.8×10 = 4.8 k 100 k Example 4 Now let’s design a 5V 50Hz square wave generator using a 555 timer. Using the circuit shown in Fig.7.11, when R2 R1, the value of p.r.f. can be calculated from: 2 0.72 p.r.f. = CR We shall use the minimum recommended value for R1 (ie, 10k ) and ensure that the value of R2 that we calculate from the formula is at least ten times larger, in order to satisfy the criteria that R2 should be very much larger than R1. When selecting the value for C, we need to choose a value that will keep the value of R2 relatively Fig.7.11. Circuit for a 5V 50Hz square wave genrator (see Example 4) 104 = 48k

753. 50 Everyday Practical Electronics, May 2011 Teach-In 2011 large. A value of 100nF should be about right, and should also be easy to locate. Making R2 the subject of the formula and substituting for C = 100nF gives: 2 -9 0.72 0.72 R = = = p.r.f.×C 50×100×10 -6 0.72 = 5×10 Hence: 6 2 0.72 × 10 R = 5 Alternatively, the graph shown in Fig.7.10 can be used. The value of R2 is more than 100 times larger than the value that we are using for R1. As a consequence, the timer should produce a good square wave output. The complete circuit of our 5V 50Hz square wave generator is shown in Fig.7.11. Check – How do you think you are doing? 7.1. Explain the difference between monostable and astable timer operation. 7.2. Sketch the circuit of a monostable timer and identify the components that determine the time for which the output is high. 7.3. Sketch the circuit of an astable pulse generator and identify the components that determine the time for which (a) the output is high, and (b) the output is low. 7.4. Design a timer circuit that will produce a 6V 20ms pulse when a 6V negative-going trigger pulse is applied to it. 7.5. Design a timer circuit that will produce a 67% duty cycle output at 250Hz. 7.6. A 555 timer is rated for a maximum output current of 120mA. What is the minimum value of load resistance that can be used if the device is to be operated from a 6V DC supply? For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/ teach-in Kitchen timer OUR kitchen timer, as shown in Fig.7.12. When SW1 is closed the buzzer will sound until SW2 is pressed to start the timer. The two probes help us to see the charge building in C1 and the status of the output. A sample trace is shown in Fig.7.13. This is particularly useful for testing long delays where the circuit may seem to being inactive. Build – The Circuit Wizard way Fig.7.13. Sample trace for the kitchen timer circuit Fig.7.14.Chargebuildingon C1 in ‘Voltage Levels’ view Similarly, in ‘Voltage Levels’ or ‘Current Flow’ we are able to visualise the charge building on the capacitor as a series of ‘+’ and ‘-’ appear on the plates (see Fig.7.14). 6 = 0.144×10 = 144k

754. Everyday Practical Electronics, May 2011 51 Teach-In 2011 The amount of elapsed time before the buzzer activates can be altered by changing the value of pot VR1. Experiment with running the timer for various settings of VR1 to ascer- tain the minimum/maximum times, THEN CONÚRM THIS USING THE APPRO- priate formulae that was introduced in ‘Learn’ (you may have to be very patient for the maximum delay!). A soft boiled egg is cooked for four minutes (240 seconds) – calculate the value required for VR1, then set this on your circuit and check out your theory in practice. ,%$ªmASHER In our second circuit (see Fig.7.15), we utilise the 555 in an astable CONÚGURATION TO GENERATE ALTERNATE ÛASHING LIGHTS 4YPICAL EXAMPLE AP- plications might include children’s toys, signs, alarm systems, and level crossings. Varying the value of VR1 'JH BTUBCMF BMUFSOBUF -% ÝBTIFS DJSDVJU TIPXO JO $VSSFOU 7JFX 'JH 5SBDF GPS BMUFSOBUF -% ÝBTIFS DJSDVJU 'JH TJNQMF CJTUBCMF mPOPGGn DJSDVJU will alter the frequency OF THE ÛASHING Circuit Wizard’s ‘Cur- rent View’ comes in to its own here for visual- ising the continuously changing state of the circuit, as shown in Fig.7.16. Apart from looking like a 70s disco, the colours clearly show how current is sinking and sourcing though the output (pin 3) as each of the LEDs is lit. You can also monitor how the capacitor charges until the threshold voltage is reached, and is then discharged through pin 7. !S WITH THE ÚRST CIRCUIT

755. THE PROBES and trace (Fig.7.16) also help us to understand the inputs and outputs. The blue probe/line showing the voltage to pin 2 and pin 6, and the red line showing the output (pin 3). /N /FFªCIRCUIT As well as using the 555 as a timer in monostable mode, it can also be used as a bistable. A neat application of this is a simple ‘on-off’ circuit, where SW1 is pressed to turn on or ‘set’ the output and SW2 is pressed to ‘reset’ or turn off the output (see Fig.7.17). A further application of this might be a signalling circuit, where SW1 is pressed to ‘set green’ and SW2 is pressed to ‘set red’, as shown in Fig.7.18. $ECADEªCOUNTER In Part 6 (-PHJD $JSDVJUT), we constructed a decade (ie, 0 to 9)

756. 52 Everyday Practical Electronics, May 2011 Teach-In 2011 counter circuit using a 4-bit ripple counter followed by a seven-segment driver and display. We used Circuit Wizard’s built in clock to test the circuit. However, in real life we would need circuitry to create this clock. The Circuit Wizard way Fig.7.18 A 555 red/green signal circuit One way of doing this would be to use a 555 configured in astable mode. Try out the circuit shown in Fig. 7.19 (if you have your 0-9 counter circuit saved from Part 6 you could amend it to include the additional components). Fig.7.19. A 0 to 9 counter circuit, with 555 an astable clock generator Dual timers In some circuits we may want to use more than one timer. The 556 IC effectively contains two 555s in one physical package. Our last circuit uses two timers ‘daisy-chained’ together to create a sequence of four ÛASHES FOLLOWED BY A GAP Fig.7.20. Tooltip showing pin description and number

757. Everyday Practical Electronics, May 2011 53 Teach-In 2011 To use both timers contained within the 556 in Circuit Wizard, you need to drag two separate in- stances of the 556 on to the circuit PAGE 4HE ÚRST TIMER WILL BE SUFÚXED ‘a’ and the second ‘b’ (eg, IC1a and IC1b). As both are contained within ONE PHYSICAL PACKAGE

758. THIS WOULD BE REÛECTED WHEN CONVERTING TO A 0# FOR EXAMPLE 5NLIKE THE SYMBOL THAT HAS NUMBERED PINS

759. #IRCUIT 7IZARD LA- BELS THE PINS OF THE VERBOSELY FOR EXAMPLE

760. THE THRESHOLD INPUT IS LABELLED l4(m !S WITH ANY INTEGRAT- ED CIRCUIT

761. BY HOVERING OVER THE PIN YOU ARE ABLE TO SEE THE PHYSICAL PIN LOCATION IN THE TOOLTIP SEE IG Construct the circuit shown in IG AND OBSERVE ITS OPERATION OTH TIMERS ARE CONÚGURED IN ASTA- BLE MODE 4HE ÚRST TIMER )#A HAS A FREQUENCY OF ABOUT (Z 4HE output from this timer is then used TO SUPPLY THE SECOND TIMER )#B WHICH HAS A FREQUENCY OF ABOUT (Z During the period when the output of timer one is high, the SECOND TIMER WILL BE ACTIVATED AND OSCILLATE FOUR TIMES

762. HENCE GIVING FOUR ÛASHES #ONVERSELY

763. WHEN THE OUTPUT OF THE ÚRST TIMER IS LOW

764. THE second timer is not powered and SO THE OUTPUT ,%$ REMAINS UNLIT 4RY EXPERIMENTING WITH THE CIRCUIT

765. perhaps changing the sequence to GIVE ONLY TWO ÛASHES BY CHANGING THE RELATIVE FREQUENCIES OF EACH timer. .OTE THAT DURING THE ÚRST lHIGHm OF EACH CYCLE BOTH FOR )#A AND )#B THE DURATION OF ENERGISED OUTPUT WILL BE SLIGHTLY LONGER 4HIS IS BECAUSE # AND # START TO CHARGE FROM 6 ON THE INITIAL CHARGE

766. RATHER THAN RD OF THE SUPPLYVOLTAGEONSUBSEQUENTCHARGES 4HISCANBESEENCLEARLYONTHETRACE BELOW

767. WHERE THE RED LINE INDICATES the output of timer one (IC1a) and the BLUE LINE

768. TIMER TWO )#B 4HIS HAS the effect that on the initial sequence only

769. THE ,%$ WILL ÛASH SEVEN TIMES rather than four! Can you design a CIRCUIT USING YOUR KNOWLEDGE FROM PREVIOUSPARTSOF Teach-In toproduce the same sequence, but without the same issues? 'JH ÝBTIFS TFRVFODF DJSDVJU 'JH ÝBTIFS TFRVFODF DJSDVJU USBDF Circuit Wizard A Standard or Professional version of Circuit Wizard can be purchased from the editorial ofﬁce of EPE – see CD-ROMs for Electronics page and the UK shop on our website (www. epemag.com). Further information can be found on the New Wave Concepts website; www.new-wave-concepts.com. The developeralsooffersanevaluationcopy of the software that will operate for 30 days,althoughitdoeshavesomelimita- tions applied, such as only being able tosimulatetheincludedsamplecircuits and no ability to save your creations.

770. 54 Everyday Practical Electronics, May 2011 Teach-In 2011 The complete circuit diagram of a variable pulse generator is shown in Fig.7.23. Look at this circuit carefully and then answer the following questions: 1. Identify the component or components that: (a) determine the pulse repetition frequency (b) provide variable adjustment of the pulse width (c) provide variable adjustment of the output amplitude (d) limit the range of variable adjustment of pulse width (e) protect IC2 against a short- circuit connected at the output (f) remove any unwanted signals appearing on the supply rail (g) form the trigger pulse required by the monostable stage. 2. Sketch waveforms to a common time scale showing the signals at (a) TPA and (b) TPB ‘test points’. 3. Determine the pulse repetition frequency of the output. day. However, with the advent of telegraph, telephone and radio in the 20th century, time signals could be broadcast internationally and made accessible to anyone that needed them. Investigate Fig.7.23. Practical circuit diagram for a variable pulse generator 4. Determine the maximum and minimum pulse width of the output. 5. Determine the maximum and minimum amplitude of the output. Amaze In last month’s Amaze we de- SCRIBED SIGNIÚCANT ADVANCES IN THE speed at which digital logic can operate. This month, we will be looking at the way in which we accurately measure time: Simple audible and visible signals were once used to inform people about the passing of time and as a means of setting their own clocks. For example, a canon could be ÚRED AT PRECISELY ONE OmCLOCK EVERY Fig.7.24. FOCS-1, a continuous cold caesium fountain atomic clock in Switzerland. The clock started operating in 2004 and keeps time to an accuracy of one second in 30 million years Fig.7.25. Atomic clocks are usually large and cumbersome devices, but much effort has been directed in making them small enough to be carried around. This is NIST’s recently developed chip-scale atomic clock

771. Everyday Practical Electronics, May 2011 55 Teach-In 2011 Modern atomic clocks are based on caesium and rubidium, and they offer uncertainties of better than one second in 20 million years. But, if that’s not good enough for you to set your watch by, the latest generation of quantum logic clocks, developed in 2008 at the National Institute of Standards and Technology (NIST) in the USA, offer an uncertainty of better than one second in over a billion years! Next month! In next month’s Teach-In, we will be looking at some applications of ANALOGUE CIRCUITS

772. INCLUDING ÚLTERS and attenuators. Since time is the reciprocal of frequency, a time standard can be easily derived from an accurate frequency standard or ‘clock’. All you need to do is count the number of cycles generated by the clock and, as long as the frequency is accurately known, the number of cycles will be an accurate measure of time. To- day’s off-air broadcast time signals use oscillators that are locked to atomic clocks. Atomic clocks 4HE ÚRST ATOMIC CLOCK USED THE VI- brations of ammonia molecules and was invented over sixty years ago. Atomic clocks use the vibrations of atoms or molecules, but because the frequency of these oscillations is so high, it is not possible to use them as a direct means of control- ling a clock. Instead, the clock is controlled by a highly stable crystal oscillator whose output is automatically multiplied and compared with the frequency of the atomic system. If two atomic clocks are compared there is always the possibility of a difference in their readings. This ‘uncertainty’ is the difference in indicated time if both were started at the same instant and later compared. For the early atomic clocks, this lack of certainty was estimated to be around one second in three thousand years. 7.1. See pages 46 and 48 7.2. See Fig.7.4 and associated text 7.3. See Fig.7.8 and associated text 7.4. See Fig.7.4 with R = 182k: and C =100nF and operating from a 6V DC supply 7.5. See Fig.7.8 with R1 = 19.2k:, R2 = 19.2k: and C = 100nF 7.6. 50:. Answers to Check questions By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! CIRCUIT WIZARD – featured in this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT See Direct Book Service – pages 75-77 in this issue * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export

773. 46 Everyday Practical Electronics, June 2011 Teach-In 2011 By Mike and Richard Tooley Part 8: Analogue Circuit Applications Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS frequency response can be altered in order to modify and enhance the We also introduce decibels (dB) Build and Investigate extend this further with a detailed look at some Amaze - I N LAST month’s instalment of Teach-In 2011 you how you can quickly and easily time delays from a few hundred nanoseconds to several hundred some practical applications of Learn we will show - produce loss or attenuation we only need a network of passive compo- - cies are to be attenuated by the same - -networks provide the required amount of attenuation) an attenuator needs to be matched to the system in which it is characteristicimpedanceoftheatten- an attenuator is correctlyterminated Learn Attenuators Attenuators provide us with a means refer to it as attenuation

774. Everyday Practical Electronics, June 2011 47 Teach-In 2011 Before we take a look at the operation of two simple forms of attenuator, it is worth pointing out that the impedances used in attenuators are always pure resistances. The reason for this is that an attenuator must provide the same attenuation at all frequencies and the inclusion of reactive components (inductors and/or capacitors) would produce a non-linear attenuation/frequency characteristic. Balanced/unbalanced The simple T and -networks that we’ve just met can exist in two basic forms, balanced and unbalanced. In the former case, none of the network’s input and output terminals are connected directly to common or ground. The unbalanced and balanced forms of the basic T and -networks are shown for comparison in Fig.8.3. The networks shown in Fig.8.3 all have two ports. One port (ie, pair of terminals) is connected to the input, while the other is connected to the output. For convenience, many two- port networks are made symmetrical and they perform exactly the same function and have the same characteristics, regardless of which way round they are connected. Please note! It is conventional to express the values of the resistances present in an attenuator in terms of the effective series or parallel resistance. Thus, for example, the two series resistors in an unbalanced T-network on whether they are based on networks of passive components (ie, resistors, capacitors and inductors) or active components (ie, transistors together with resistors, capacitors and/or inductors. The symbols used to represent - matic diagrams are shown in Fig.8.4. attenuation of signals below their cut-off frequency. Beyond the cut-off frequency, they exhibit increasing amounts of attenuation, as shown in Fig.8.5. A simple C-R shown in Fig.8.6. The cut-off fre- the output voltage has fallen to attenuator are both labelled R1/2 where R1 is the effective series resistance. Similarly, the two parallel resistors present in an unbalanced -network are labelled 2R2 where R2 is the effective resistance of the two components when connected in parallel. We will be adopting a similar convention when we label the cir- Filters Filters provide us with a means of passing or rejecting signals within are used in a variety of applications, - mitters and receivers. They also provide us with a means of reducing noise and unwanted signals that might otherwise be passed along power lines. Filters are usually described according to the range of frequencies that they will accept or reject. The following types are possible: Low-pass High-pass Band-pass Band-stop. Filters can also be categorised as either passive or active, depending Fig.8.1. Basic T and -network attenuators Fig.8.2. A matched network Fig.8.3. Balanced and unbalanced forms of the T and -networks

775. 48 Everyday Practical Electronics, June 2011 Teach-In 2011 0.707 of the input value. This occurs when the reactance of the capacitor, XC, is equal to the value of resistance, R. Using this information we can determine the value of cut-off frequency, f, for given values of C and R: Since Please note! The term ‘cut-off’ can be a bit mis- leading because it might imply that beyond a certain point. This is not the case. The response of a practical the cut-off frequency and one of the most important characteristics roll-off occurs. R = XC or 1 2 R fC from which: 1 2 f CR where f is the cut-off frequency (in Hz), C is the capacitance (in F), and R is the resistance (in ). attenuation of signals above their increasing amounts of attenuation, as shown in Fig.8.7. A simple C-R shown in Fig.8.8. Once again, the when the output voltage has fallen to 0.707 of the input value. This occurs when the reactance of the capacitor, XC, is equal to the value of resistance, R. Using this information we can determine the value of cut-off frequency, f, for given values of C and R: Since R = XC or 1 2 R fC and once again: 1 2 f CR where f is the cut-off frequency (in Hz), C is the capacitance (in F), and R is the resistance (in ).

776. Everyday Practical Electronics, June 2011 49 Teach-In 2011 Example 1 A simple C-R C = 100nF and R = 10k using: -XL f0: 1 2 f CR 9 4 1 6.28 100 10 10 10 100 15.9 Hz 6.28 Example 2 A simple C-R 1 2 R fC 3 9 1 6.28 1 10 47 10 6 10 3.39 k 295.16 - pass-band - a lower cut-off frequency f1 an upper cut-off frequency f2 f2 – f1 bandwidth A simple L-C an L-C acceptor circuit. resonant XC XC = XL 0 0 1 2 2 f L f C 2 0 2 1 4 f LC 0 1 2 f LC f0 L and C qualityfactor Q-factor R f0 L and R - stop-band - alowercut-offfrequency f1 an upper cut-off frequency f2 f2 – f1 bandwidth 0 0 2 1Bandwidth f f f Q 02 f L R Fig.8.9. Frequency response for a Fig.8.10. A simple L-C band-pass Fig.8.11. Frequency response for a Fig.8.12. A simple L-C band-stop Hz k

777. 50 Everyday Practical Electronics, June 2011 Teach-In 2011 A simple L-C band-stop filter is shown in Fig.8.12. This circuit uses an L-C resonant circuit and is referred to as a rejector circuit. The frequency at which the band- - mum attenuation occurs when the circuit is resonant, ie, when the reactance of the capacitor, XC, is equal to the reactance of the inductor, XL. This information allows us to determine the value of frequency at the centre of the pass-band, f0: frequency at which minimum attenuation will occur. The frequency of minimum attenuation will be given by: XC = XL 0 0 1 2 2 f L f C thus from which 2 0 2 1 4 f LC and thus 0 1 2 f LC where f0 is the resonant frequency (in Hz), L is the inductance (in H) and C is the capacitance (in F). determined by its quality factor (or Q-factor). This, in turn, is largely determined by the loss resistance, R, of the inductor (recall that a practical coil has some resistance as well as inductance). Once again, the bandwidth is given by: 0 0 2 1Bandwidth f f f Q 02 f L R where f0 is the resonant frequency (in Hz), L is the inductance (in H), and R is the loss resistance of the inductor (in ). Example 3 A simple acceptor circuit uses L = 2mH and C = 1nF. Determine the Fig.8.13. The characteristic impedance (Z0) of a network is determined by the values of resistance (or impedance) within the network – see text 0 1 2 f LC 3 9 1 2 2 10 1 10 6 10 112.6 kHz 8.88 Example 4 A 15kHz rejector circuit has a Q-factor of 40. Determine the bandwidth of the circuit. The bandwidth can be found from: 3 0 15 10 Bandwidth 375 Hz 40 f Q 375 Hz kHz Hz Termination, matching and characteristic impedance an attenuator to be predictable we need to take into account the input (source) and output (load) impedances. These impedances are said to terminate them into account the performance can be somewhat unpredictable! When a filter or attenuator is correctly terminated it is said to be matched. Analogue systems are often designed so that they have a particular input/source and output/ load impedance. In many audio systems the impedance chosen is 600 but in radio frequency (RF) applications impedances of 50 , 75 or 300 are common. It is often convenient to analyse the behaviour of a signal transmis- sion path in terms of a number

778. Everyday Practical Electronics, June 2011 51 Teach-In 2011 of identical series connected networks. One important feature of any number of identical symmetrical networks are connected in series, the resistance (or impedance) seen looking into the network will have a as the characteristic impedance of the network identical networks are connected in seen looking into this arrangement will be equal to the characteristic impedance, Z0. Now suppose that we remove the - poses, we will still be looking into an see an impedance equal to Z0 when we look into the network. impedance of Z0 across the output terminals of the single network that exactly the same way as the arrange- by correctly terminating the network in its characteristic impedance, we have made one single network section appear the same as a series of identical networks stretching to Z0) of a network is determined by the values of resistance (or impedance) within the network, as we shall see next. C-R and L-C we have described in earlier sections have far from ideal characteristics. are used and a selection of these (based on matched T-section and -section networks) are shown in these circuits are as follows: where Z0 is the characteristic impedance (in ), fC is the cut-off frequency (in Hz), L is the inductance (in H), and C Example 5 Determine the cut-off frequency and - Fig.8.14. Improved T-section and 0 L Z C Comparing the circuit shown in type with L C (note that the value of C is the effective series capacitance and is - tors connected in series). Now and C 1 2 f LC 0 C2 Z L f C 0 1 2 C f Z C 1 2 f LC 3 9 1 6.28 5 10 20 10 5 10 1.59 kHz 6.28 3 3 0 9 5 10 5 10 20 10 20 L Z C 3 0.5 10 500 : Capacitance: Characteristic impedance: Cut-off frequency: kHz

779. 52 Everyday Practical Electronics, June 2011 Teach-In 2011 The simple R-C filters that we described earlier in Fig.8.6 and Fig.8.8 require a very low source impedance and a very high load impedance in order to behave in a predictable manner (ie, to satisfy the equation for cut-off frequency that we met earlier). One way of improving the performance of these buffer, as shown in Fig.8.16 and Fig.8.17. These circuits maintain the predicted frequency response, but the rate at which the output voltage falls above cut-off may be Fortunately, we can easily solve this problem by exploiting the gain available from the operational am- popular second-order Sallen and that can be obtained with the simple The cut-off frequency of the second-and Fig.8.17. Later, in Build you will have the opportunity to build and test these circuits. One of the most important parameters of an analogue circuit is the amount of gain or loss that it provides. Gain can be expressed in various ways, but basically it is just the ratio of output to input expressed in terms of either voltage, current or power. Since gain and loss can sometimes be quite large we often use a logarithmic scale to express our ratios. This measurement is based on decibels (dB), where one decibel is equivalent to one tenth of a Bel (the logarithm of the voltage, current or power ratio). In case this is beginning to sound a little complicated we have summarised all of this in Table 8.1. Table 8.1. Gain or loss expressed in decibels of voltage, current and power Basis of measurement Gain or loss as a ratio Gain or loss expressed in decibels (dB) Voltage out in V V out 10 in 20log V V Current out in I I out 10 in 20log I I Power out in P P out 10 in 10log P P

780. Everyday Practical Electronics, June 2011 53 Teach-In 2011 Please note! Example 6 A 0 1 2 1 1 2 2 f C R C R C1 = C2 = C R1 = R2 = R 0 1 2 f CR out V 10 10 10 in 20log V A V 10 2 20log 0.02 Example 7 Now P out 10 in 10log P A P loss Check – How do you think you are doing? 8.8. Fig.8.20. See Question 1 P A 10 out 10 in log P P 1020log 100 20 2 40 dBdB 8.1. 8.2. L-C L-C 8.3. R C 8.4. 8.5. L-C 8.6. L-C L-C 8.7. 10 10 6 antilog 10 out 10 in antilog 0.6 P P P out out 10 10 10antilog 10 A out out 10 10 in in antilog log P P P P out in 10antilog 0.6P P 1.6 0.25 0.4 WW Please note!

781. 54 Everyday Practical Electronics, June 2011 Teach-In 2011 WE ARE now going to try out and see how they behave when we apply different signals to them. One of the features that Circuit higher-end electronics packages is the ability to directly carry out AC this would involve modelling the - the software ‘sweep’ through the frequency range and plot the output amplitude and phase. There are a number of useful appli- 5Spice Analysis (www.5spice.com). to use unless you are familiar with similar SPICE analysis programmes. it just can’t keep up in real-time. the simulation speed in order to give the software a chance to accurately simulate. - - gree to get your traces looking right. Speed trap Under certain circumstances Circuit Wizard will warn you about accurate high speed simulation (see Fig.8.21). present you with bizarre results with no warning. Fig.8.22 shows an simulated in real time! Changing the simulation speed is achieved by clicking on ‘Time:’ selecting an appropriate timing (see Fig.8.23). Note that this only appears when the simulation is running. showninFig.8.24below.Thisisanac- the output terminals and voltage rails for the supply to the operational am- mistake that students make. Please note that in order for our Circuit Wizard circuits to match the circuit diagrams you have seen in Learn you will need to ‘mirror’ the Although Circuit Wizard can’t do still does a great job of modelling We can then bring our results together and plot our own frequency understand what’s really going on and what happens to the signals as we vary the frequency of the input. Circuit Wizard carries out literally thousands of mathematical calculations in the background in order to show you how the circuit operates working with higher frequency Fig.8.21. Simulation speed warning Fig.8.22. The bizarre result of simulating a high frequency circuit in real-time Fig.8.23 (below). Changing simulation speed

782. Everyday Practical Electronics, June 2011 55 Teach-In 2011 the inverting (‘-’) input is at the top (see Fig.8.25). Using your new knowledge from Learnyoushouldbeabletocalculate the cut-off frequency to be around 159Hz. This means that we should expect it to happily pass low frequency signals below this frequency and reject high frequency signals. In order to test this out we’ll simulate the circuit with various frequencies and record the amplitude of the output. We can then plot this in Excel and see the characteristics Start by simulating the circuit with a 1Hz input frequency (ie, set the frequency of the function generator to 1Hz – Circuit Wizard will do this happily in real time. You should alter the properties of the graph as follows; maximum: 6V, minimum: 6V, time: 200ms. Your trace should look similar to Fig.8.26. You should also notice that the output (blue) and input (red) are basically identical, meaning that the signal has passed directly through Now change the frequency of the signal generator to 100Hz. You will also need to decrease the simulation speed and graph properties. These were 5ms and 2ms in the author’s case, but you should experiment to get the best results. The resulting waveform is show in Fig.8.27. Notice that the amplitude has been reduced or attenuated to around 4.2V, and the output waveform has been delayed and is out of phase. Experiment with various frequencies between 1Hz and 200Hz, recording your results. When you have a number of results plot them on a graph with frequency along the x-axis and amplitude along the y-axis. If you are using Excel to plot the graph, make sure that you select the ‘scatter’ graph type, as this will

783. 56 Everyday Practical Electronics, June 2011 Teach-In 2011 correctly plot the two values against each other. Fig.8.28 shows our results taking readings every 10Hz. essentially swapping the capacitor and resistor. You should now have in Fig.8.29. Experiment to see how the output changes with different frequencies from 1Hz to 600Hz recoding your results and plotting them on frequencies are attenuated while higher frequencies are passed un- altered. You should also notice that the lower the frequency the higher the phase difference. Our results are shown in Fig.8.30. Now we’re going to ramp things up a little and look at second-order filters. Fig.8.31 and Fig.8.32 show a low-pass and high- pass second-order Use your theory knowledge from Learn to calculate the cut-off frequency for each circuit and use this to help you select an appropriate frequency range to test the circuit. Simulate the circuit and collect a series of results in order to help you producegraphsforeachcircuitshow- ing how they respond. Fig.8.28. Graph showing the response of the low-pass Fig.8.30. Graph showing the response of the high-pass

784. Everyday Practical Electronics, June 2011 57 Teach-In 2011 Last, we are going to produce a and paste your two second - - For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/teach-in 8.1. C-R - 8.2. 8.3. 8.4. 8.5. 8.6. 8.7 8.8 By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! CIRCUIT WIZARD – featured in this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT See Direct Book Service – pages 75-77 in this issue * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export

785. 58 Everyday Practical Electronics, June 2011 Teach-In 2011 The data shown in Table 8.2 was obtained during an experiment on an active tone control. Plot the frequency response curve using the logarithmic grid shown in Fig.8.35 and use it to determine: (a) the maximum value of voltage gain (in dB) (b) the maximum value of voltage gain (expressed as a ratio) (c) the approximate voltage gain at 50Hz and 30kHz (d) the two frequencies at which the voltage gain falls to zero (e) the range of frequencies over -1dB of the maximum Investigate Frequency (Hz) 20 40 70 100 200 700 1k 2k 4k 7k 10k Voltage gain (dB) -3 +5 +12.5 +15 +16 +16 +16 +16 +16 +15 +12.5 20k 40k 60k +5.5 -2 -7.5 (f) the two frequencies at which the gain has fallen by 6dB from its maximum value. Fig.8.35. See Investigate Amaze In most electronic circuits, the signal voltages that we have to deal with range from a few millivolts to a few volts. Similarly, the power levels present in these circuits tend also to be rather modest and usually range from a few milliwatts to a few examples where signal voltages and power are either very much smaller or very much larger than this. When you receive a signal on your radio or TV at home, the signal voltage present at the input of the radio or TV receiver is often only a few tens or hundreds of microvolts. Since the impedanceoftheaerial,coaxialcable andinputofthereceiverisinvariably 75 , this suggests that, for a signal of 1 mV, the actual power present at the input of your radio or TV will be in the region of: (digital) to reach an estimated view- ing population of 11 million people. digital power output will increase tenfold to 200kW. Ifitwerepossibletoabsorballofthe currently radiated 1MW of analogue power in a single 50 ohm resistor the voltage generated across the ends of the resistor would be given by: This 50-foot dish antenna at the North Kennedy Space Center is supplied with a power of 3kW from a C-band radar to produce an effective radiated power (ERP) of around 3MW! 232 6 R 1 10 10 75 75 V P Z 0.0133 W At the other extreme, consider the power that is delivered to the aerial of a high power transmitting station. This is very much larger. For example, the Crystal Palace TV transmitter currently radiates a power of 1MW (analogue) and 20kW 6 1 10 50V P R 7.07 kV If the 1MW of radiated power from you, the Boshakova transmitter (used until recently by the Voice of Russia) produced a staggering 2.5MW of output, and its output was radiated by no less than eight guyed masts, each around 250 metres tall. Next month! look at digital-to-analogue and analogue-to-digital conversion. Table 8.2. W

786. Products Catalog 2011 …from engineers to engineers 50W Audio Power Amplifier HT-AV50W 50+ watts from a 12V battery power supply !! This integrated power output amplifier consists of little more than one integrated circuit. It is intended especially for use in motor vehicles and other battery operated applications. Although it appears simple and hardly worth looking at, the amplifier can produce an appreciable audio power output ! High power output through Class-H operation 80Wx2 Class-D Audio Power Amplifier HT-AU280 With efficiencies as high as 94% - compared to around 50% for Class-AB amplifiers… The required installation space is very small thanks to the extremely compact construction. This is primarily made possible by the very high efficiency of the PWM output stage (up to 94%), which reduces the complexity of the circuit and minimises the cooling footprint. http://www.handsontec.com HandsOn Technology

787. 46 Everyday Practical Electronics, July 2011 Teach-In 2011 By Mike and Richard Tooley Part 9: Digital-to-Analogue and Analogue-to-Digital Conversion Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS I N THIS instalment of Teach-In 2011, we introduce some combined applications of analogue and digital circuits in the form of digital-to-analogue and analogue- to-digital converters (DAC, ADC). In Learn we explore the circuits and techniques used in DAC and ADC. Investigate extends this further with a look at a popular DAC, which is available from several semiconductor manufacturers. Build looks at some further applications of digital circuits using both combinational and sequential logic techniques. Finally, in Amaze we look at the way that very large numbers are handled in digital systems. Quantisation Becausesignalsintherealworldexist in both digital (on/off) and analogue (continuouslyvariable)forms,digital andcomputersystemsneedtobeable to accept and generate both types of signal as inputs and outputs respectively. Because of this, there is a need for devices that can convert signals in analogue form to their equivalent in digital form, and vice versa. This chapter introduces digital- to-analogue and analogue-to-digital conversion. We shall begin by looking at the essential characteristics of analogue and digital signals and the principle of quantisation. In order to represent an analogue signal using digital codes, it is necessary to approximate (or quantise) the signal into a set of discrete voltage levels, as shown in Fig.9.1 The sixteen quantisation levels for a simple analogue-to-digital converter using a four-bit binary code are shown in Fig.9.2. Note that, in order to accom- modate analogue signals that have both positive and negative polarity we have used the two’s complement representation to indicate negative voltage levels. Thus, any voltage represented by a digital code in which the MSB (most - tive. Fig.9.3 shows how a typical analogue signal would be quantised Learn

788. Everyday Practical Electronics, July 2011 47 Teach-In 2011 into voltage levels by sampling at regular intervals (t1, t2, t3, etc). Digital-to-analogue conversion The basic digital-to-analogue converter (DAC) has a number of digital inputs (often 8, 10, 12, or 16) and a single analogue output, as shown in Fig.9.4. The simplest form of DAC shown in Fig.9.5(a) uses a set of binary-weighted resis- and a four-bit binary latch to store the binary input while it is being converted. connected in inverting mode, the analogue output voltage will be negative rather than positive. How- stage can be added at the output to change the polarity if required. The voltage gain of the inputs to the operational amplifier (determined by the ratio of feedback to input resistance and taking into ac- is shown in Table 9.1. If we assume that the logic levels produced by the four-bit data latch are ‘ideal’ (such that logic 1 corresponds to +5V and logic 0 corresponds to 0V), we can determine the output voltage corresponding to the eight possible input states by summing the voltages that will result from each of the four inputs taken independently. Forexample,whentheoutputofthe latch takes the binary value 1010 the outputvoltagecanbecalculatedfrom: Fig.9.1. The process of quantising an analogue signal into its digital equivalent Fig.9.2. Quantisation levels for a simple ADC that uses a four-bit binary code Fig.9.3. An analogue signal quantised into voltage levels by sampling at regular intervals (t1, t2, t3, etc.) Fig.9.4. Basic DAC representation Similarly, when the output of the latch takes the binary value 1111 (the maximum possible) the output voltage can be determined from: Table 9.1.Table of voltage gains for the simple DAC shown in Fig.9.5(a) Vout = (–1 × 5) + (–0.5 × 0) + (–0.25 × 5) + (–0.125 × 0) = –6.25V Vout = (–1 × 5) + (–0.5 × 5) + (–0.25 × 5) + (–0.125 × 5) = –9.375V Bit Voltage gain 3 (MSB) –R/R = –1 2 –R/2R = –0.5 1 –R/4R = –0.25 0 (LSB) –R/8R = –0.125

789. 48 Everyday Practical Electronics, July 2011 Teach-In 2011 The complete set of voltages corresponding to all eight possible binary codes is given in Table 9.2. Binary-weighted DAC An improved binary-weighted DAC is shown in Fig.9.5(b). This circuit operates on a similar principle to that shown in Fig.9.5(a), but uses four analogue switches instead of a four-bit data latch. The analogue switches are controlled by logic inputs so that a switch’s output is connected to the reference voltage (Vref) when its respective logic input is at logic 1, and to 0V when the corresponding logic input is at logic 0. When compared with the previous arrangement, this circuit offers the advantage that the reference voltage is considerably more accurate and stable than using the logic level to A further advantage arises from the fact that the reference voltage can be made negative, in which case the analogue output voltage will become positive. Typical reference voltages are –5V, –10V, +5V and +10V. Unfortunately, by virtue of the range of resistance values required, the binary-weighted DAC becomes increasingly impractical for higher resolution applications. Taking a 10-bit circuit as an example, and assuming that the basic value of R is 1k , the binary weighted values would become: Bit 0 1k Bit 2 2k Bit 3 4k Bit 4 8k Bit 5 16k Bit 6 32k Bit 7 64k Bit 8 128k Bit 9 256k Fig.9.5. Simple DAC arrangements Bit 3 Bit 2 Bit 1 Bit 0 Output voltage 0 0 0 0 0V 0 0 0 1 –0.625V 0 0 1 0 –1.250V 0 0 1 1 –1.875V 0 1 0 0 –2.500V 0 1 0 1 –3.125V 0 1 1 0 –3.750V 0 1 1 1 –4.375V 1 0 0 0 –5.000V 1 0 0 1 –5.625V 1 0 1 0 –6.250V 1 0 1 1 –6.875V 1 1 0 0 –7.500V 1 1 0 1 –8.125V 1 1 1 0 –8.750V 1 1 1 1 –9.375V Table 9.2. Output voltages produced by the simple DAC shown in Fig.9.5(a)

790. Everyday Practical Electronics, July 2011 49 Teach-In 2011 R-2R Accuracy and resolution Please note! The resolution Please note! The accuracy Filters Analogue-to-digital conversion Fig.9.6. Filtering the output of a DAC Fig.9.7. Basic ADC representation

791. 50 Everyday Practical Electronics, July 2011 Teach-In 2011 voltage present at the inverting input stage, the output of that stage will go to logic 1. So, assuming that the analogue input voltage is 2V, the outputs of IC1 and IC2 will go to logic 1 while the remaining outputs will be at logic 0. The priority encoder is a logic device that produces a binary output code that indicates the value of the one of its inputs. In this case, the output of IC2 will be the most sig- output code generated will be 010 (as shown in Fig.9.8(b). Flash ADC are extremely fast in operation (hence the name), but they become rather impractical as the resolution increases. For example, while a 10-bit ADC would need a staggering 1024 comparator stages! Typical conversion times for a 1 s, so this type of ADC is ideal for ‘fast’ or rapidly changing analogue signals. Due to their complexity, flash ADC are relatively expensive. Successive approximation A successive approximation ADC is shown in Fig.9.9. This shows an 8-bit converter that uses a DAC (usually based on an R-2R ladder) together comparator (IC1) and a successive approximation register (SAR). The 8-bit output from the SAR is applied to the DAC and to an 8-bit output latch. A separate end of conversion (EOC) signal (not shown in Fig.9.9) is generated to indicate that the conversion process is complete and the data is ready for use. When a start conversion (SC) signal is received, successive bits within the SAR are set and reset according to the output from the comparator. At the point at which the output from the comparator reaches zero, the analogue input voltage will be the same as the analogue output from the DAC and, at this point, the conversion is complete. The end of conversion signal is then generated and the 8-bit code from the SAR is read as a digital output code. Successive approximation ADCs Fig.9.9. A successive approximation ADC Fig.9.10. A ramp-type ADC

792. Everyday Practical Electronics, July 2011 51 Teach-In 2011 types and typical conversion times (ie, the time between the SC and EOC signals) are in the range 10 s to 100 s. Despite this, conversion times are fast enough for most non-critical applications, and this type of ADC is relatively simple and available at low-cost. Ramping it up A ramp-type ADC is shown in Fig.9.10. This type of ADC comparator, IC1. The output of the comparator is either a 1 or a 0 depending on whether the input voltage is greater or less than the instantaneous value of the ramp voltage. The output of the comparator is used to control a logic gate (IC2) which passes a clock signal (a square wave of accurate frequency) to the input of a pulse counter whenever the input voltage is greater than the output from the ramp generator. Fig.9.11. Waveforms for a single-ramp ADC The pulses are counted until the voltage from the ramp generator exceeds that of the input signal, at which point the output of the comparator goes low and no further pulses are passed into the counter. The number of clock pulses counted will depend on the input voltage and the representation of the analogue input. Typical waveforms for the ramp-type waveform are shown in Fig.9.11. Dual-slope ADC - ment of the ramp-type ADC, which Check – How do you think you are doing? 9.6. The binary codes produced by a four-bit bipolar analogue-to- digital converter (see Fig.9.2 and Fig.9.3) sampled at intervals of 1ms, have the following values: 9.1.Explainwiththeaidofasketch what is meant by quantisation. 9.2. A DAC can produce 256 different output voltages. What is the resolution of the DAC? 9.3. How many discrete voltage levels can be produced by a 10- bit DAC? 9.4. Explain the advantage of an R-2R ladder DAC compared a binary-weighted DAC. 9.5. ADC and suggest an application in which it can be used. Fig.9.12. Waveforms for a dual-ramp ADC If the ADC uses two’s complement to represent negative values (ie, 1111 represents -1, 1110 represents -2, and so on) sketch and identify the waveform of the analogue voltage. Time (ms) Binary code 0 0101 1 0100 2 0011 3 0010 4 0001 5 0000 6 1111 7 1110 For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/ teach-in

793. 52 Everyday Practical Electronics, July 2011 Teach-In 2011 IN this edition of Build we will try out some of the DAC circuits that we introduced in Learn (Fig.9.5). As we have seen, these can be con- with cleverly arranged arrays of input resistors. Binary-weighted DAC Firstenterthesimplebinary-weighted DAC circuit shown in Fig.9.13. This is a practical circuit based on the one shown in Learn Fig.9.5(a). We have used a series of logic input toggles to simulate standard logic level inputs, with the output voltage shown on a virtual voltmeter instrument. Set various input bit patterns and monitor the resulting output voltage. Using your theory from Learn to calculatetheexpectedoutputvoltage for two different input bit patterns and then test your answers using the simulation. Take readings of the output voltage for the binary coded decimal inputs from 0 (0000) to 15 (1111) and produce a graph of your results. Fig.9.14 shows our example results plotted using Microsoft Excel. Fig.9.13. A simple four-bit binary-weighted DAC Fig.9.14. Graph of results for the simple four-bit binary-weighted DAC Fig.9.16. Graph of results for four-bit binary- weighted DAC shown in Fig. 9.15 involvesasimilarcomparatorarrange- ment, but uses an internal voltage negative ramp which starts when the positive going ramp reaches the analogue input voltage. The important thing to note about this type of ADC is that, while the slope of the positive ramp depends on the input voltage, Hence,thistypeofADCcanprovide averyhighdegreeofaccuracyandcan also be made so that it rejects noise and random variations present on the input signal. The main disadvantage, ramping up and then ramping down requires some considerable time, and hencethistypeofADCisonlysuitable for‘slow’signals(ie,thosethatarenot rapidlychanging).Typicalconversion times lie in the range 500 s to 20ms.

794. Everyday Practical Electronics, July 2011 53 Teach-In 2011 One of the drawbacks to the simple DAC circuit is the fact that by - put is negative. A common way of dealing with this issue is to add an a gain of -1. This is often referred to as a unity gain inverter. Modify your binary-weighted DAC circuit (Fig.9.13) to that shown in Fig.9.15 below, and experiment with changing the input bits. Notice that - tude to the output voltage (Vout) but opposite in polarity. Plotting Vout against BCD input for this new arrangement should now look as shown in Fig.9.16. binary-weighted DAC is shown in Fig.9.17. Here the output voltage is taken across the outputs of In this way the output voltage is effectively doubled. In fact, this method is commonly employed in many commercial DAC integrated circuit devices. Fig.9.18. Binary-weighted DAC using analogue switches and a negative voltage reference Fig.9.19. Four-bit DAC using an R-2R ladder arrangement Fig.9.17. Improved binary weighted DAC with differential output A switch in time In Fig.9.5(b) we described an improved DAC circuit using analogue simply for simulation purposes using single-pole double-throw (SPDT) switches, as shown in Fig.9.18. Note that in a real circuit these would be controlled by logic inputs. Simulate the circuit by changing the binary input patterns by tog- gling switches SW1 to SW4. Notice that by having a negative reference voltage we achieve a positive output voltage. Experiment by changing the reference voltage (Vref) and note how this affects the output voltage range. On the ladder Finally, we will try out a third type of DAC circuit that utilises a so called R-2R resistor ladder arrangement, like that shown earlier in Fig.9.5(c). As we discussed in Learn, there are practical advantages to this type of one matched pair of resistor values. Construct the circuit shown in Fig.9.19 and experiment with the simulation. Build – The Circuit Wizard way

795. 54 Everyday Practical Electronics, July 2011 Teach-In 2011 ADCs and DACs invariably take the form of integrated circuit devices. Obtain data sheets for a DAC0800 digital-to-analogue converter (these can be freely downloaded from the websites of semiconductor manufacturers like National Semicon- ductor and Motorola) and use them to answer each of the following questions: 1. How many data bits are used? 2. What range of supply voltages can be used with this device? 3. What package styles are used for Investigate the device and how many connecting pins do the packages have? 4. What is the typical power con- sumption of the device when used with a ±10V supply? 5. What is the absolute maximum power dissipation for the device? 6. Which pins are used for (a) the LSB input and (b) the MSB input? 7. On what principle does the DAC operate? 8. What is the typical time taken for the output voltage to settle in response to a change at the input? 9.1. See page 46 and Fig.9.1 9.2. 8-bit 9.3. 1024 9.4. Only two values are needed in the resistor chain of an R-2R ladder (the ratio of the two resistances is more important than their absolute values). The resistance values in a binary-weighted DAC can become very large when a large number of bits are used 9.5. High speed of operation. A typical application would be for use with high-quality audio and video signals (ie, analogue signals at relatively high frequencies) 9.6. Falling ramp (the analogue value falls linearly) Answers to Check questions Amaze As you have seen, the resolution of a DAC or ADC is determined by the number of data bits that it uses. The simple four-bit DAC that you met in Build was only capable of generating sixteen different voltage states. By increasing the number of bits we can gain a corresponding increase in produce 32 different output voltages, a six-bit DAC is able to produce 64 different output levels, and so on. In many applications, the digital output of an ADC is processed using a computer or some form of embedded processor (such as those used in the engine control and management systems of motor vehicles). The unit of data in a computer (ie, the number of bits that can be handled by its processing unit as one single entity) is referred to as a word. So, ultimately, the digital output of an ADC must be converted into words that the computer or embedded system’s processor can operate on. The number of bits in a word is an important characteristic of a particular processor family or computer architecture. This, in turn, has an impact on the size and range of the quantities that it can manipulate. Early computers, such as the IBM PC and Commodore Amiga, as well as early console systems, such as the Sega Genesis, Super Nintendo, Mattel Intellivision, used a word length of 16-bits. This allowed them to manipulate integer numbers having a total of 65,536 different values. More powerful 32-bit computers (such as the Apple Macintosh, Pentium-based PC and popular console systems, including the Sony PlayStation, Nintendo GameCube, Xbox, and Wii) have word lengths of 32-bits and this allows them to manipulate integer numbers that can represent 4,294,967,296 different values. However, if that’s not quite enough in terms of resolution, the most recent 64-bit systems including some games consoles, such as Nintendo 64, PlayStation 2, Play- Station 3, Xbox 360, can cope with integer numbers having a staggering 18,446,744,073,709,551,616 different values! Next month! In next month’s Teach-In we will look at practical aspects of test instruments, measurements and testing circuits (including an introduction to PCB layout using Circuit Wizard). By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! CIRCUIT WIZARD – featured in this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT. See Direct Book Service – pages 75-77 in this issue * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export

796. HandsOn Technology http://www.handsontec.com 1 USB-RS232 Interface Card: HT-MP213 A compact solution for missing ports… Thanks to a special integrated circuit from Silicon Laboratories, computer peripherals with an RS232 interface are easily connected to a USB port. This simple solution is ideal if a peripheral does not have a USB port, your notebook PC has no free RS232 port available, or none at all ! After a slow and faltering start, the USB port has become commonplace on PCs, to the extent that the latest GHz machines have just one RS232 port left, or none at all. The compact USB-RS232 interface described in this article allows your good old RS232 peripherals (printer, programmer system, etc.) to be hooked up to a USB port. The free driver programs for Win 2000/XP, Linux and Apple Macintosh make the interface virtually transparent, enabling the USB port to behave like a regular COM interface. The driver and the conversion chip from Silicon Laboratories allow a full serial data link to be set up on a 9-way RS232 connector, including all handshaking signals. 1. THE SILICON LABORATORIES CP2103 SYSTEMS OVERVIEW The CP2103 is a highly-integrated USB-to-UART Bridge Controller providing a simple solution for updating RS- 232/RS-485 designs to USB using a minimum of components and PCB space. The simplified block diagram of the CP2103 is shown in Figure 1 and the pin assignment, in Figure 2. Royalty-free Virtual COM Port (VCP) device drivers provided by Silicon Laboratories allow a CP2103-based product to appear as a COM port to PC applications. The CP2103 UART interface implements all RS-232/RS-485 signals, including control and handshaking signals, so existing system firmware does not need to be modified. The device also features up to (4) GPIO signals that can be user-defined for status and control information. Support for I/O interface voltages down to 1.8 V is provided via a VIO pin. In many existing RS-232 designs, all that is required to update the design from RS-232 to USB is to replace the RS-232 level-translator with the CP2103. Silicon Laboratories has taken care of the PC side of things by supplying royalty-free Virtual COM Port (VCP) device drivers. If you've ever used a PC RS-232-to-USB converter, you know that it looks like a standard COM port to the PC and its applications. The VCP device driver also pretends to be a standard COM port. That means that we can use our newly acquired microcontroller USB interface to communicate with a Tera Term Pro terminal window on a computer just as if we were using RS-232 hardware on the embedded side. 2. HT-MP213 USB-to-RS232 CONVERTER BOARD The HT-MP213 is designed to transition a piece of hardware from an RS-232/485 interface to a USB interface. We were attracted to the CP2103 because of its skinny schematic diagram. If we believe what the CP2103 datasheet schematic is telling us, it doesn't require any external resistors or crystals to bring a fully compliant USB 2.0 interface to life. The silicon encapsulates a level 2.0 full-speed function controller, transceiver, EEPROM, oscillator, and UART in a tiny QFN-28 package. The internal EEPROM is used for storing vendor-specific information in commercial applications. If we find that we need to access the EEPROM, there is easy access and programming via its USB interface.

797. 42 Everyday Practical Electronics, August 2011 Teach-In 2011 By Mike and Richard Tooley Part 10: Electronic circuit construction and testing Our Teach-In series aims to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced reader with you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS T HIS month, we look at the practical aspects of electronic circuit construction and testing. In Learn we introduce you to two of the most common and versatile items of test equipment, the multimeter and oscilloscope. Build looks at techniques that can be used to design, construct and test printed circuit boards (PCB) within Circuit Wizard. Investigate involves taking measurements and Finally, Amaze looks at the reliability of electronic components. Learn At BTEC Level 1 and Level 2 you need to be able to make measurements on simple DC and AC circuits including: Measuring voltage, current and resistance using a multi-range meter (or multimeter) Displaying waveforms and making measurements of voltage (peak and peak-to-peak) and time using an oscilloscope. Fig.10.1. Multimeters can be either analogue (left) or digital (right)

798. Everyday Practical Electronics, August 2011 43 Teach-In 2011 estimation of the pointer’s position, and then the application of some mental arithmetic based on the range switch setting (see Fig.10.2) Unlike their analogue counterparts, digital multimeters are usually extremely easy to read and have displays that are clear, unam- biguous, and capable of providing a very high resolution. It is also possible to distinguish between readings that are very close. This is just not possible with an analogue instrument. Digital multimeters offer a number - pared with their analogue counter- multimeter usually consists of a 3½-digit seven-segment display— digit is either blank (zero) or 1. In all cases, you will need to ensure that you work safely and observe correct procedures (for example, switching off and disconnecting the power supply before connecting test leads). We begin this month’s Learn by introducing the test instruments that you will be using. Multimeters One of the most common, versatile and easy-to-use instruments is the multi-range meter, or multimeter. This instrument combines the functions of a voltmeter, ammeter and ohmmeter into a single instrument. Many multimeters also have additional ranges, for example to check continuity, measure capacitance or to check diodes and transistors. Most multimeters operate from internal batteries, and are thus independent of the mains supply. This allows you to easily carry them around and make measurements on electronic equipment when you are away from the laboratory or workshop. There are two main types of multimeter: analogue and digital (see Fig.10.1). Analogue multimeters employ conventional moving coil form of a pointer moving across a calibrated scale. This arrangement is not so convenient to use as that employed in digital instruments because the position of the pointer is rarely exact and may require interpolation. Analogue instruments do, however, offer some advantages, not least, is that it’s very easy to make adjustments to a circuit, while observing a movement in one direction repre- senting an increase and in the other a decrease. Despite this, the main disadvantage of analogue meters is the rather cramped and sometimes confusing scale calibration. To determine Fig.10.2. A comparison of the displays provided on analogue and digital multimeters. Both meters indicate the same value. Fig.10.3. The procedure for making current and voltage measurements using a digital multimeter

799. 44 Everyday Practical Electronics, August 2011 Teach-In 2011 Consequently, the maximum indication on the 2V range will be 1.999V. This suggests that the instrument is capable of offering a resolution of 1mV on the 2V range (in other words, the smallest incre- ment in voltage that can be measured is 1mV). Depending on the size and calibration markings on the instrument’s scale, the resolution obtained from a comparable analogue meter would typically be about 50mV, and so the digital instrument provides us with a resolution that is many times greater than its analogue counterpart. Multimeter measurements The procedure for making current and voltage measurements using a digital multimeter, is shown in Fig.10.3. We’ve chosen this type of instrument for our example because you will probably be using a modern digital instrument rather than an older analogue type. Note how it is necessary to break the circuit and insert the meter when making a current measurement. No- tice also how the voltmeter is connected in parallel with the circuit at the point at which you are making a measurement. It is essential that you get these two connections right and that you select the correct ranges on the multimeter. Failure to observe these two simple precautions can result in damage to the meter and/or the circuit under test! In Fig. 10.3, one of the meters is used to measure the supply current (note that the circuit must be broken and the meter inserted into it), while the second instrument is being used to measure the potential difference (voltage drop) across diode D1. The initial range settings (200mA for the current measurement, and 20V for the voltage measurement) are chosen so that they are both greater than those that we would expect to in the circuit to be (9 – 5.6)/100 amps or 34mA. Similarly, we could assume that the voltage that we would measure shouldbe5.6V(thesameastheZener voltage), but in no event would we expect it to be greater than the supply voltage (9V). We have, therefore, left quite a margin for safety with the two ranges that we’ve selected! Please note! It is essential to switch off and disconnect the power supply before attempting to connect test leads. When the meter ranges have been set and theconnectionsmade,thesupplycan be reinstated and switched back on, so that measurements can be made. Please note! In your school/college course you will only be working with equipment that uses safe low voltage supplies. Even so, it is essential to observe Health and Safety precautions whenever you are working on live electrical and electronic circuits. When in doubt, you should always refer to your tutor! Please note! When the circuit on test uses large value capacitors it may be necessary to wait a few minutes in order to allow them to discharge safely before making connections to the circuit. Please note! Make sure that you only use properly insulated test leads to make connections to a circuit on test. The leads clips and probes to make connections to a circuit. Never use bare wires and test prods as these can cause short-circuits to adjacent connections! Oscilloscopes Oscilloscopescanbeusedinavariety of measuring applications, the most important of which is the display of time related voltage waveforms. Older oscilloscopes (Fig.10.4) used cathode ray tubes (CRT) for their displays. In order to make accurate measurements, the face of the CRT graticule that was either integral with the tube or took the form of a separate translucent sheet. Modern oscilloscopes use monochrome, which incorporate an electronically generated measuring scale. Accurate voltage and time measurements are made with reference to the scale or graticule, applying a scale factor derived from the appropriate range switch. The use of the graticule is illus- trated by the following example. An oscilloscope screen is depicted in Fig.10.5. This diagram is reproduced at a reduced size. If shown full-size, thegraticalmarkingswouldbespaced wouldbeevery2mmalongthecentral vertical and horizontal axes. The oscilloscope is operated with position. The timebase (horizontal Fig.10.4. A typical two-channel general purpose oscilloscope that uses a CRT display

800. Everyday Practical Electronics, August 2011 45 Teach-In 2011 virtual instruments - Please note! - calibrate - Oscilloscope measurements - - - Virtual instruments - Fig.10.5. Using an oscilloscope scale supply Fig.10.7. A typical display produced by a PC-based virtual oscilloscope

801. 46 Everyday Practical Electronics, August 2011 Teach-In 2011 Control Adjustment Focus Provides a correctly focused display on the screen Intensity Adjusts the brightness of the display Astigmatism Provides a uniformly defined display over the entire screen area and in both x and y directions. The control is normally used in conjunction with the focus and intensity controls Trace rotation Permits accurate alignment of the display with respect to the graticule (CRT displays only) Scale illumination Controls the brightness of the graticule or scale Horizontal deflection system Timebase (time/cm) Adjusts the timebase range and sets the horizontal time scale. Usually this control takes the form of a multi-position rotary switch and an additional continuously variable control is often provided. The ‘CAL’ position is usually at one, or other, extreme setting of this control Stability Adjusts the timebase so that a stable waveform display is obtained Trigger level Selects the particular level on the triggering signal at which the timebase sweep commences Trigger slope This usually takes the form of a switch that determines whether triggering occurs on the positive or negative going edge of the triggering signal Trigger source This switch allows selection of one of several waveforms for use as the timebase trigger. The options usually include an internal signal derived from the vertical amplifier, a 50Hz signal derived from the supply mains, and a signal which may be applied to an External Trigger input Horizontal position Positions the display along the horizontal axis (CRT displays only) Vertical deflection system Vertical attenuator (V/cm) Adjusts the magnitude of the signal attenuator (V/cm) and sets the vertical voltage scale. This control is invariably a multi-position rotary switch; however, an additional variable gain control is sometimes also provided. Often this control is concentric with the main control and the ‘CAL’ position is usually at one, or other, extreme setting of the control Vertical position Positions the display along the vertical axis of the display AC-DC-ground Normally an oscilloscope employs DC coupling throughout the vertical amplifier; hence a shift along the vertical axis will occur whenever a direct voltage is present at the input. When investigating waveforms in a circuit, one often encounters AC superimposed on DC levels; the latter may be removed by inserting a capacitor in series with the signal. With the AC- DC-ground switch in the DC position, a capacitor is inserted in the input lead, whereas in the DC position the capacitor is shorted. If ground is selected, the vertical input is taken to common (0V) and the oscilloscope input is left floating. This last facility is useful in allowing the accurate positioning of the vertical position control along the central axis. The switch may then be set to DC and the magnitude of any DC level present at the input may be easily measured by examining the shift along the vertical axis. Chopped-alternate This control, which is only used in dual-beam CRT oscilloscopes, provides selection of the beam splitting mode. In the chopped position, the trace displays a small portion of one vertical channel waveform followed by an equally small portion of the other. The traces are, in effect, sampled at a relatively fast rate, the result being two apparently continuous displays. In the alternate position, a complete horizontal sweep is devoted to each channel alternately. Table 10.1. Oscilloscope controls and adjustments AC

802. Everyday Practical Electronics, August 2011 47 Teach-In 2011 Check – How do you think you are doing? (b) Focus (c) Stability (d) Trigger source (e) Vertical attenuator. 10.5. Explain why it is important to ensure that the variable controls of an oscilloscope are placed in the ‘CAL’ position before attempting to make an accurate measurement. 10.6. What adjustment should be made to an oscilloscope when it is to be used to display a small AC voltage superimposed on a much large DC voltage? Explain why this adjustment is necessary. 10.1. Briefly explain the difference between analogue and digital multimeters. Which type of instrument offers the greatest resolution? Why is this? 10.2. What indications are displayed on the analogue and digital multimeters shown in Fig.10.8? 10.3. What information (eg, amplitude, period) can be obtained from the oscilloscope displays shown in Fig.10.9? 10.4. Explain the function of each of the following oscilloscope controls: (a) Brightness Fig.10.8. See Question 10.2 Fig.10.9. See Question 10.3 For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/ teach-in By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! CIRCUIT WIZARDCircuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT. See Direct Book Service – pages 75-77 in this issue 1 ms/cm

803. 48 Everyday Practical Electronics, August 2011 Teach-In 2011 A soft touch IN previous instalments of Build, we’ve been using Circuit Wizard to simulate and test various circuits in order to demonstrate electronic theory. However, in this edition, we are going to look at the process of taking an electronic circuit and converting it to a printed circuit board (PCB) design that can be produced for real. This is one of the real gems of the Circuit Wizard software as you’ll see later on. We will try out some of the software’s automatic conversion tools, as well as investigating some of the more advanced functionality. Once you’ve completed this tutorial you should be ready to enter, test and convert your own circuits to a PCB design. The electronics industry is heavily reliant on software throughout the product design cycle. An example design cycle for an electronic circuit is shown in Fig.10.10. A designer might use various tools and calculators to design the initial circuit. The circuit would then be drawn in an electronic format in a process known as schematic capture. The circuit may then be simulated and analysed using a Simulation Program with Integrated Circuit Emphasis (SPICE). SPICE software runs thousands of calculations on each junction point or node of a circuit, taking into account all of the components. There are various types of analysis that can be carried out: information can be displayed in real time (as in Circuit Wizard) to show a virtual simulation, or gathered and presented in reports or graphs/ charts to show how a circuit functions over time and/or with varying characteristics. In this way a designer can be pretty sure that a circuit will operate correctly before spending time and money producing the physical board. Once the information from the circuit is then used to generate a PCB design ready for production and testing of the circuit. On the board So, let’s get to work and see Circuit Wizard in action generating a PCB! Start off by entering the circuit shown in Fig.10.11; a basic potential divider-based automatic light circuit. Ensure that you get all of the component values and connections correct. Once you’ve entered the circuit, run a quick simulation to make sure that it functions correctly. Press the ‘Run’ button on the toolbar and raise/lower the light level on the LDR (R2) to ensure that the LED (D1) lights under low light conditions). Now we’re ready to begin the conversion process. Click on the ‘Convert to PCB Layout’ button on the toolbar (Fig.10.12), or alternatively use the menu to navigate through ‘Project’, ‘Circuit Symbols’ then ‘Convert to PCB Layout…’. This will start a short wizard to guide you through the conversion process. Click ‘Next’ to continue to the next screen, where you will be asked to select a board type (single or double-sided) and a track size. For most home/school low voltage DC projects, with a relatively low component count and where space and component density is not a premium, we would suggest normal tracks on a single-sided board. Build – The Circuit Wizard way for an electronic circuit circuit ready for conversion to a PCB layout

804. Everyday Practical Electronics, August 2011 49 Teach-In 2011 Therefore, select ‘Single-Sided; Normal Tracks’ and then click on ‘Next’. The next screen allows us to change the size and shape of the board. In this case, we’ll leave these as the default and click on ‘Next’. crossed! As Circuit Wizard carries out the conversion of your circuit to a PCB, it will animate the placing of the components, followed by the calculation of the optimum track layout. If all goes well, after from yours. It should be noted that the automatic routing functionality of Circuit Wizard is a little limited, and it does struggle to route much more than the simplest circuits without a little help. However, we’ll be looking at tactics for cre- ating more complex PCBs later in this article. Now that we have created our PCB layout, there are a number of exciting things that we can do with it. A superb feature of Circuit Wizard is that as well as simulating the circuit Make sure that you select the Off- board Component variant, not a PCB Component. Wire the PP3 battery’s positive and negative connections to the two-pin screw terminal block by dragging from the ends of the battery connector wires (Fig.10.14). Virtual test You are now ready to virtually test your PCB; start the simulation using the ‘Run’ button on the toolbar, as you would for a standard circuit, and try out the function of the circuit by changing the light level on the LDR. On the left-hand side of the screen you may select various different views of the PCB. The default is ‘Real World’, which shows a full colour representation of what the board will actually look like when constructed. ‘Normal’ is a more tra- ditional PCB design view. As with schematic simulation, the PCB may also be simulated in a ‘Current Flow’ and ‘Logic Level’ view. In ‘Current Flow’ view, the tracks are colour coded depending on the instantaneous voltage and ‘marching of current (Fig. 10.16). This is particularly useful for understanding the operation of the circuit, as well a short period of time you should receive a completion message de- tailing the success of your conversion (Fig.10.13). Closing this should reveal your new PCB layout! Fig.10.14 shows our example PCB layout; this may vary slightly Fig.10.12 (above left). The ‘Convert to PCB layout’ toolbar button Fig.10.14. Example PCB layout for the simple light-operated switch circuit in Fig.10.11, and wiring the PP3 9V battery to the PCB schematic, you can also simulate a virtual copy of your PCB design. attach a suitable power supply. Drag and drop across a PP3 9V battery from the Off-board Components in the Component Gallery (Fig.10.15). Fig.10.15. Off-board Components in the Component Gallery

805. 50 Everyday Practical Electronics, August 2011 Teach-In 2011 Build – The Circuit Wizard way as providing a comparison for fault Design output - - drilling. More complex circuits - Fig.10.16. Current Flow view of the PCB Fig.10.17. The Circuit Wizard PCB print menu Fig.10.18. Circuit Wizard’s CAD/CAM menu

806. Everyday Practical Electronics, August 2011 51 Teach-In 2011 that you receive a routing message similar to that shown in Fig.10.20, explaining that the software was unable to completely convert your circuit automatically. In our example, you can see that you may be more or less successful to completely route using the automatic routing feature. Inspecting the it is impossible to wire the circuit, just that the software was unable to we can step in here to make the job of the software a little easier. Rats nest However, this time select ‘Rats Nest; Fig.10.22. The pins of the components are mass of criss-crossing wires is often We now have to place the com- simply placing components at ran- is to place the components so that We might also require components so that it locates in the right place To achieve the former, it is essentially a case of placing the components so that there are as few cross-overs of green lines as possible. Hence, this will make the job of rout- Fig.10.20. Automatic routing message for the circuit of Fig.10.19 Fig.10.21. The generated PCB layout showing incomplete routing Fig.10.22. Starting point for the ‘rats nest’ PCB layout

807. 52 Everyday Practical Electronics, August 2011 Teach-In 2011 Build – The Circuit Wizard way links.Aswellascomponentposition, their orientation may be altered by rotation(keyboardshortcutCTRL+R). Notice that as you move components to a new location, the green lines will update to the nearest common point for that net. This allows rats nest prior to routing the tracks. Fig.10.23 shows an example layout which places the battery connector at the edge of the board and attempts to leave the rats nest as clean as possible. On track At this point we can either start to draw our tracks manually in-line with the green nets, or instruct Circuit Wizard to attempt to automatically route the board now that we have prepared the component personal preference is to have the software route the tracks automatically, then go in and modify the results as required to achieve a the individual user to experiment and decide upon their favoured approach. To initiate automatic routing, click (Fig.10.24). Our completed auto Fig.10.23. Improved layout using ‘rats nest’ technique Fig.10.25. The completed auto-routed layout Fig.10.24. Selecting automatic routing from the PCB Layout Tools menu Fig.10.26. The track button Fig.10.27. A manually added PCB track routed layout looks as shown in Fig. 10.25. The layout is now complete and ready for virtual simulation and output for production. If you prefer to draw the tracks manually (or indeed if Circuit Wiz- ard fails to route your circuit automatically) select the track button from the toolbar (Fig.10.26). Tracks are started by left-clicking with additional segments added by further right-clicking. Previous users of PCB drafting - tice for it to become intuitive. You view for manual track drawing. Fig.10.27 shows a track manually added to the 555 circuit. A number of additional PCB con- available through the PCB wizard. On the second screen, tick ‘Allow me to customise the PCB layout con- with many additional options as you proceed through the conversion process. One of these additional con- the physical component mappings. When converting to a PCB, Circuit Wizard selects the most appropriate PCB component footprint based on the component variant and values selected. However, there may be times when you wish to specify a different model from that chosen by default. The screen shown in Fig.10.28 will be included in the wizard when the tick box is checked as described earlier, allowing you to alter the package

808. Everyday Practical Electronics, August 2011 53 Teach-In 2011 used for each component (in this case showing the package selection window for the battery, B1). On the subsequent wizard screen you are given a number of component placement options. An interesting option is ‘Take into account component positions’. When Circuit Wizard converts to a PCB it tries to order the components as you have set them out on your schematic. This may be convenient for keep- ing component numbering sequential. However, in practice this is not always the best way to place com- automatically routing and/or the components are being placed in a Fig.10.28. Specifying different component models Fig.10.29. An example of a Quality Check Report poor manner, try unticking this option. This can have a dramatic effect on the results. Finally, one really useful tool is Qual- ity Check. This may be accessed from the PCB Layout Tools icononthetoolbar,or by selecting ‘Project’, ‘PCB Components’ then ‘Quality Check’ from the menu. This will analyse the PCB layout in comparison to your circuit diagram, to ensure that all of the connections have been made correctly, as well as various other checks. This is particularly useful when routing manually to check the con- nectivity of your design. Fig.10.29 shows an example Quality Check Report. We’ve really only scratched the surface of the PCB conversion and drafting tools within Circuit Wizard. As with any software tool, the best way to learn more is to get ‘hands on’ and use the software. In the next edition of Build we’ll be giving you the opportunity to do just that with a range of project circuits for you to enter, test, convert and build using all of the skills you’ve learnt throughout the series. Answers to Check questions 10.1 See page 43 and page 44 10.2 (a) 83.0mA AC (b) 180 10.3 (a) Sine wave; 5ms period (frequency = 200Hz); amplitude 6V pk-pk (b) Pulse wave; 8ms period (p.r.f. = 125Hz; high time = 2ms, low time 6ms; 25% duty cycle (mark-to-space ratio = 1:3; (amplitude 2.5V pk-to-pk 10.4 See page 46 and Table 10.1 10.5 See page 45 and Table 10.1 10.6 See page 46 and Table 10.1

809. 54 Everyday Practical Electronics, August 2011 Teach-In 2011 Fig. 10.30 shows a simple regulated power supply and three common items of test equipment. 1. Photocopy the diagram and add connecting wires to the diagram in order to show: (a) How the collector current of transistor TR1 is measured (b) How the base-emitter voltage of TR1 is measured. 2. For (a) and (b) above, list the initial adjustments that should be made to the test equipment. 3. If the output voltage of the circuit is meas- uredat0Vandtheinputvoltageas15.1V,what measurements would you make, and in what order,tolocatethefault?Explainyouranswer. Amaze Investigate In our everyday lives we are increasingly reliant on highly complex electronic systems that involve large numbers of individual component parts. However, because each individual part can be prone to failure, we need to ensure that each component has a very high reliability in order to ensure that the equipment as a whole remains free from failure. Reliability (ie, the ability to operate without failure) is thus a paramount considerationforthoseinvolvedwith the design of electronic equipment. To put this into context: suppose that we know that one out of every 100000 of a particular component type is likely to break down every hour. This implies that an item of equipment that makes use of 100 of these components would break down at an average interval of 1000 hours or less than 42 days operation. In many cases this would be woe- fully inadequate! The requirement for a very high degree of reliability is crucial in many applications. In satellite com- munications, the electronics is often expected to operate for at least 20 yearswithoutfailure,simplybecause itwouldbeimpossibletorecoverand repair the satellite without spending far more than the satellite was actually worth. Added to this, there would beconsiderablelossofrevenuewhile the satellite was out of service: in many cases this might amount to millions of pounds or dollars. The failure rate of individual com- ponentsdependsonthesituationand environment in which they are used. Asatelliteexperiencesextremeforces and temperatures during launch and In consequence, the environment in which a satellite operates is con- sidered severe when compared with that in which most consumer elec- reason, we need to ensure that only the most reliable types of electronic component are used in satellites. But just how reliable are the elec- troniccomponentsusedinthecircuits that you construct? A single low-cost metal oxide resistor operated within itsratingandinabenignenvironment canbeexpectedtoahaveworkinglife of more than 1000 years. The same to have a reliability that is at least ten times and preferably more than 100 times greater than this! Next month! In next month’s Teach-In 2011 we round up the series with a brief look back at previous parts. We shall also be including some fun revision activities as well as essential reference information. Our series con- cludes with a selection of electronic projects that you can build and test using Circuit Wizard. Fig.10.30. See Investigate

810. HandsOn Technology http://www.handsontec.com 1 ISP to ICP Programming Bridge: HT-ICP200 In-Circuit-Programming (ICP) for P89LPC900 Series of 8051 Flash μController… …ICP uses a serial shift protocol that requires 5 pins to program: PCL, PDA, Reset, VDD and VSS. ICP is different from ISP (In System Programming) because it is done completely by the microcontroller’s hardware and does not require a bootloader… That the 80C51-based controllers are extremely popular is nothing new, certainly when considering the large number of designs that can be found on the web. The reason may well be the fact that the tools (both hardware and software) that are available for this controller are very affordable and there is an enormous amount of information readily available. In addition, a very active forum provides answers to many questions. One of the most significant features of the P89LPC900 Family is that the core now requires only 2-clock Cycles Per Instruction (CPI). 8051 experts will already know that this used to be 12 or 6 cycles until now. In practice, this means that the crystal frequency can be drastically lowered to achieve the same processing speed as their classic counter parts. ISP Programming is only available for 20, 28 and 44pin parts. IAP is only available once your IAP program has been loaded in to the LPC900 part. ICP -can be used to program all the LPC900 parts. The LPC90x devices can only be programmed using a ICP programming method. In contrast to some of the larger LPC900 family members, the LPC90x devices do not offer other programming methods like Parallel Programming, In- System Programming (ISP) or complete In-Application Programming (IAP). HOWEVER - ICP requires hardware control/ signaling of the LPC900 to be programmed. In some high-end applications, there may be a need to replace the code in the microcontroller without replacing the IC itself. This article described in detail the operation of the In-Circuit-Programming (ICP) capability which allows these microcontrollers to be programmed while mounted in the end product. P89LPC9xx parts (affectionately know as the LPC900 series of micro-controllers) can be programmed 4 ways... 1. ISP (In-System-Programmed) using the UART of the LPC900. 2. IAP (In-Application-Programmed) .. or self programmed by reprogramming the flash under code execution. 3. ICP (In-Circuit-Programming)... using Synchronous Serial.... Similar to SPI signaling - each data bit is clocked in/out under clock signal control. 4. Parallel Programmer, available in expensive industry grade tools. 1. INTRODUCTION HT-ICP200 P89LPC900 Target Application Board To communicate between a PC (running Flash Magic) and the LPC900 Micro-Controller to be programmed an ICP Bridge circuit is required as shown in Figure 1. Figure 1: Hooking up ICP to the P89LPC900 Application Board

811. 46 Everyday Practical Electronics, September 2011 Teach-In 2011 By Mike and Richard Tooley Part 11: Summing it all up Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have attempted to provide coverage of three of the most important electronics units that are currently studied in many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge TEACH-IN 2011 A BROAD-BASED INTRODUCTION TO ELECTRONICS I N THIS instalment of Teach-In 2011, we bring our series to a conclusion with a quick review of the previous ten parts, and include a comprehensive index that will help you to locate the key topics that we’ve introduced as the series has progressed. There’s also a selection of questions and fun activities, including a crossword, that will help you to check your understanding. For good measure, we’ve also included eight additional circuits for you to investigate using the Circuit Wizard software. We began our Teach-In series by looking at the signals that are used to convey information in electronic circuits. We discussed the units and quantities that we use when making measurements in electronic circuits, and how waveforms are used to show how the voltage and current in an electronic circuit vary with time. We also introduced batteries and power supplies that we use to provide power to electronic circuits. Part 2 dealt with resistors, capacitors, timing circuits and Ohm’s Law. We also found out what happens when a capacitor is charged or discharged. Part 3 provided you with an introduction to diodes and power supplies. We investigated the voltage/ current characteristics for two different types of diode, and showed how they could be used together with a transformer to produce a power supply. We also looked at light emitting diodes (LEDs) and Zener diodes. Learn

812. Everyday Practical Electronics, September 2011 47 Teach-In 2011 Crossword Check – How do you think you are doing? 11.1. Solve the crossword shown in Fig.11.1. Clues across 5 Amplitude (4) 7 Instrument for measuring current (7) 8 Polarised capacitor (12) 10 Commonly used for logarithmic ratios (7) 15 Most positive connection of an NPN transistor (9) 18 Very common type of waveform (4) 19 Stores electric charge (9) 20 Unit of potential difference (4) 21 Instrument used to display waveforms (12) 22 P in PRF (5) 26 Mostpositiveconnectionona conductingdiode(5) 27 ×0.000001 (5) 29 Peak or maximum value (9) 30 Unit of frequency (5) Clues down 1 Used to produce delays (5) 2 Diode voltage reference (5) 3 Present on the plates of a capacitor (6) 4 Time for one cycle (6) 6 Circuit that has no stable state (form of oscillator) (7) 9 direction only (5) 11 C in CRT (7) 12 13 Fast analogue-to-digital converter (5) Transistors were the subject of Part 4. We described the operation of NPN and PNP transistors, and explained how they are used to amplify current and operate as saturated switches. An introduction to operational of Part 5. We showed how opera- in inverting, non-inverting and differential arrangements, as well as showing how they could be used as comparators, where one voltage is compared with another. Logic circuits were explained in Part 6. Here we met the symbols, truth tables and Boolean logic for each of the most common types of logic gate. We also introduced bistable devices, and showed how they could be used in binary counters. The highly versatile electronic timer (555/6) was introduced in Part 7. These versatile circuits can be used to produce accurate time delays and repetitive pulse waveforms. Analogue circuit applications, in were described in Part 8. We explained the characteristics of low- and showed how these could be built using simple arrangements of resistors, capacitors and inductors. We also introduced some simple active The month’s Check panels provides you with an opportunity to test your understanding of the previous ten parts of our Teach-In 2011 series. 14 ×1,000,000 (4) 16 Steps alternating voltage up or down (11) 17 Most positive connection of a PNP transistor (7) 19 Smallest indivisible part of a battery (4) 23 L in LED (5) 24 Unit of capacitance (5) 25 ×0.001 (5) 28 Unit of resistance (3) Crossword solution – page 53

813. 48 Everyday Practical Electronics, September 2011 Teach-In 2011 Check – How do you think you are doing? The next question tests your ability to recognise the symbols used in circuit diagrams: 11.2. Identify each of the symbols shown in Fig.11.2. Question11.3 and Question 11.4 test your ability to extract information from a waveform: 11.3. For the waveform shown in Fig.11.3(a): (a) What type of waveform is shown? (b) What is the frequency of the waveform? (c) What is the periodic time of the waveform? (d) What is the amplitude (peak value) of the waveform? 11.4. For the waveform shown in Fig.11.3(b): (a) What type of waveform is shown? (b) What is the pulse repetition frequency of the waveform? (c) What is the periodic time of the waveform? (d) What is the duty cycle of the waveform (e) What is the peak-peak value of the waveform? Fig.11.2 See Question 11.2 Fig.11.3 (right). See Question 11.3 and Question 11.4 measure, we explained how decibels are used to express gain or loss in electronic circuits. In Part 9, we showed how an analogue signal can be converted to digital data, and vice versa. We described the process of quantisation and explained how the number of data bits affects the accuracy and resolution of a DAC and ADC. Part 10 dealt with the practical aspects of constructing and testing electronic circuits. We introduced some basic items of test equipment in the form of multimeters and oscilloscopes, and showed how these could be used to measure voltage, current, frequency, time and waveform in an electronic circuit.

814. Everyday Practical Electronics, September 2011 49 Teach-In 2011 Quantity Unit Abbreviation Electric potential Volt Ampere A Electric power W Capacitance F Resistance Ohm Frequency Hz Bit rate Bps Definition Unit The potential that appears between two points when a current of 1 Ampere flows in a circuit having a resistance of 1 Ohm The current that flows in an electrical conductor when electric charge is being transported at the rate of 1 Coulomb per second 1 Watt The resistance of a circuit when a current of 1 Ampere flowing in it produces a potential difference of 1 Volt 1 Hertz Question 11.7 tests your ability to convert multiples and sub-multiples to fundamental units: The next two questions test your knowledge of some of the units and quantities used in electronics: 11.5. Complete the table of electrical quantities and units of measurement 11.6. 11.7. Express: (a) 250mV in V (b) 0.15mA in A (c) 68000 in k (d) 0.235W in mW (e) 0.22M in k (f) 885Hz in kHz (g) 1500pF in nF (h) 1.2kbps in bps The next question tests your ability to recognise some common electronic components: 11.8. needed to build a simple astable LED Question 11.9 checks a basic understanding of basic digital logic: 11.9. (a) a four-input AND gate can be built (b) a four-input OR gate can be built Finally, Question 11.10 tests your ability to read and understand a simple electronic circuit diagram: 11.10 - ance of ±5%. - - Fig.11.5. See question 11.10 Fig.11.4. See question 11.8 The answers to these questions are shown on page 54 volt ampere ohm The potential that appears between two points when a current of one ampere flows in a circuit having a resistance of one ohm The current that flows in an electrical conductor when electric charge is being transported at the rate of one coulomb per second The resistance of a circuit when a current of one ampere flowing in it produces a potential difference of one volt 1 watt 1 hertz

815. 50 Everyday Practical Electronics, September 2011 Teach-In 2011 OVER the Teach-In series, our Build section has put theory into practice using Circuit Wizard to simulate a whole range of electronic circuits. We’ve shown how using simulation software is great for allowing you to really get to the bottom of how a circuit actually operates, as well as being a crucial tool for electronic designers. In this, the last edition we are giving you the opportunity to try out your ‘wizard’ skills with a selection of practical circuits that you can enter and investigate. For each circuit, we’ve included a brief description, along with some suggestions for experimentation and a few questions to help test and extend your understanding of the underpinning theory. These circuits are a great starting point for your own projects and circuit designs. COIN TOSS Description The circuit shown in Fig.11.6 uses a J-K speed. When switch SW1 is pressed, at 1kHz (that’s one thousand times a second). During this time, the LEDs will ap- dimly lit. When the button is released, and hence one LED will remain lit to signify either ‘heads’ or ‘tails’. The circuit is not truly random, but because the output is changing so quickly it would be hard to get a consistent output by timing the button press. Investigate: 1. We’ve used the in-built clock device – try to create your own clock generator (perhaps using a 555 astable or a Schmitt oscillator circuit). 2. The coin toss circuit is not truly Build – The Circuit Wizard way random – how could we generate a real random selection? 3. How could we extend the circuit to give six outputs – ie, to create an electronic dice? Fig.11.6. Coin toss circuit diagram EGG TIMER Description The egg timer circuit shown in Fig.11.7 is a classic 555 bistable circuit. Switch SW1 selects between a soft-boiled (~3 min) and hard-boiled (~5 min) egg by changing the resistor through which capacitor C1 is charged. When the circuit is powered, the buzzer (BZ1) will sound until switch SW2 is pressed to start the timer. For this reason a practical version of this circuit should include a further toggle switch to connect/disconnect the power supply. Investigate: 1. Monitor the charge on capacitor C1 by placing a probe on pin-6/7. 2. Use the theory that you learnt in Part 2 to calculate the time period for the circuit when timing both soft- and hard-boiled eggs (note that resistor R3 is in series with either R1 or R2 when you calculate the total resistance through which C1 is charged). 3.Howwouldyoualterthecircuittogiveafour-minuteegg? Fig.11.7. Egg timer circuit diagram

816. Everyday Practical Electronics, September 2011 51 Teach-In 2011 KNIGHT RIDER LIGHTS Description In Fig.11.8, a 4017 decade counter is used to produce a ‘running lights’ sequence illumi- nating each LED in turn. Each LED is connected to two outputs, so that as the 4017 counts up further, the LEDs are lit again in reverse order. This gives the effect of the LEDs running alternately forward/backwards. Investigate: 1. The speed of the lights can be varied by ‘adjusting’ potentiometer VR1. Check that this works. Fig.11.8. Knight Rider ‘chaser’ lights 2. The 4017 is clocked by a simple Schmitt oscillator circuit (IC1a). Use the Internet and/or other resources to devices and how they may be used to make a simple clock signal. 3. What is the purpose of diodes D1 to D8? INTRUDER ALARM Description The circuit shown in Fig.11.9 uses a thyristor (or silicon controlled particular device before, but it acts as a latch to hold the circuit in the ‘on’ state once pushswitch (push-to- break) SW1 is pressed. The alarm will remain on until the circuit is disconnected from the battery (for example with keyswitch SW2), even if SW1 is released. Switch SW1 could be replaced with a normally closed (NC) pressure pad, a trip wire or a door contact in a real circuit. Investigate: 1. Extend the circuit to include more than one trigger. 2. Use the Internet and/or other re- works. 3. What would happen if (a) resistor R1 became open-circuit or (b) if transistor Q1 became short-circuit between collector and emitter? Fig.11.9. Circuit diagram for a simple intruder alarm For more information, links and other resources please check out our Teach-In website at: www.tooley.co.uk/ teach-in 4. Why is only one series resistor (R10) required?

817. 52 Everyday Practical Electronics, September 2011 Teach-In 2011 Build – The Circuit Wizard way PUSH-ON/PUSH-OFF CONTROL SWITCH Description In Fig.11.10, a J-K flip-flop is clocked on/off when pushswitch (push-to-make) SW1 is pressed. The Schmitt trigger inverter (IC2a) and capacitor C1 are used to de- Q1, which in turn allows current (RL1), and hence completes the mains voltage circuit and powers the light on and off. Investigate: do we need to reduce it? 2. What would happen if SW1 was 3. What is the purpose of diode D1? 9V BATTERY TESTER Description breakdown voltage Zener diodes to control red, amber and green LEDs on test. Investigate: be different values? 2. What would the effect be of changing the breakdown voltage of the Zener diodes? 5V, 12V etc.? Fig.11.10. Circuit for a push-on/push-off control switch Fig.11.11. An LED 9V battery tester circuit By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from start to ﬁnish – even including on-screen testing of the PCB prior to construction! CIRCUIT WIZARD – featured in this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package. Two versions are available, Standard and Professional. This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90 inc. VAT. See Direct Book Service – pages 75-77 in this issue * Circuit diagram design with component library (500 components Standard, 1500 components Professional) * Virtual instruments (4 Standard, 7 Professional) * On-screen animation * PCB Layout * Interactive PCB layout simulation * Automatic PCB routing * Gerber export

818. Everyday Practical Electronics, September 2011 53 Teach-In 2011 METRONOME Description A 555 timer is used in Fig.11.12 in an - Investigate: TEMPERATURE- CONTROLLED FAN Description Investigate: - Fig.11.12. Metronome circuit using a 555 timer IC Fig.11.13 (above). Temperature-controlled fan circuit Fig.11.14 (right). Answer to Question 11.1

819. 54 Everyday Practical Electronics, September 2011 Teach-In 2011 Answers to Check questions 11.1. See Fig.11.14 11.2. (a) switch (SPST) (k) preset potentiometer sistor (BJT) 11.3. (a) sinewave (b) 40Hz (c) 25ms 11.4. (b) 5ms (c) 200Hz 11.5. 11.6. 11.7. (b) 150 A (c) 68k (e) 220k (f) 0.885kHz (g) 1.5nF (h) 1200bps. 11.8. (a) resistors (4) (b) preset potentiometers (2) (e) transistors (2) 11.9. See Fig. 11.15 11.10. (b) PNP transistor (h) R2. Fig.11.15. Answer to Question 11.9 Round-up Teach- In 2011 in a C-R t Mike and Richard Tooley

820. Everyday Practical Electronics, September 2011 55 Teach-In 2011 555 timer 4-53, 7-44, 7-45 556 timer 7-46, 7-53 741 operational amplifier 5-48 ADC 1-51, 9-49, 9-51 AND logic 6-45, 6-47 Acceptor circuit 8-49 Accuracy 9-49 Active filter 8-50 Ampere 1-51, 2-51 Amplitude 1-53 Analogue meter 10-43 Analogue signal 1-51, 9-47 Analogue-to-digital conversion 1-51, 9-46, 9-49 Anode 3-48 Astable oscillator 4-55 Astable pulse generator 7-48 Attenuators 8-46 Automatic light switch 5-56 Automatic routing 10-49 BJT 4-46, 4-47, 4-48, 4-49 Balanced attenuator 8-47 Band-gap reference 9-49 Band-pass filter 8-47, 8-48, 8-57 Band-stop filter 8-47, 8-48 Bandwidth 5-51, 8-50 Base 4-46 Batteries 1-54 Bias 3-48, 4-50 Binary 6-49, 9-46 Binary-weighted DAC 9-48, 9-52 Bipolar junction transistor 4-46, 4-47 Bistable 6-48 Bits per second 1-51 Block schematic 1-55 Boolean logic 6-46 Bridge rectifier 3-50 Buffer 6-46 C-R circuits 2-54 C-R high-pass filter 8-48 C-R low-pass filter 8-48 CLEAR input 6-48, 6-49 CMOS 6-50 CRT 10-44 Capacitors 2-53, 2-57, 2-58 Cathode 3-48 Cathode ray tube 10-44 Cells 1-54 Characteristic impedance 8-50 Charge 2-54 Circuit Wizard 1-56, 10-48 Collector 4-46 Collector load 4-50 Colour code 2-52 Combinational logic 6-47 Common base 4-48 Common collector 4-48 Common emitter 4-48 Common-emitter amplifier 4-49, 4-51 Comparator 5-53, 5-55 Complex waveform 1-52 Counter 7-52 Current 1-51 Current gain 4-49, 4-53, 5-50, 8-50 Current measurement 10-43, 10-44 Cut-off frequency 5-52, 8-51, 8-49 D-type bistable 6-48, 6-50 DAC 1-51, 9-47, 9-49 DIL package 6-50 Darlington transistor 4-48 Decade counter 6-54 Decay 2-55 Decibels 8-50 Depletion mode MOSFET 4-48 Dielectric 2-53 Differential amplifier 5-52 Digital logic 6-44 Digital meter 10-43 Digital signal 9-47 Digital-to-analogue conversion 9-47 Digital-to-analogue converter 1-51 Diode characteristics 3-49, 3-51 Diodes 3-48, 3-52 Discharge 2-54 Dual timer 7-52 Dual-in-line 6-50 Dual-slope ADC 9-51 Duty cycle 1-54 Electric charge 2-54 Electrolytic capacitor 2-53 Emitter 4-46 Energy storage 2-54 Enhancement-mode MOSFET 4-48 Equivalent circuit 5-50 Exclusive-NOR logic 6-46, 6-47 Exclusive-OR logic 6-46, 6-47 Exponential decay 2-55 Exponential growth 2-55 FET 4-46, 4-47 Feedback 4-51 Field effect transistor 4-46, 4-47 Filters 8-47, 8-51 Fixed resistor 2-51 Flash ADC 9-50 Follower 5-52, 5-53 Forward bias 3-48 Frequency 1-53 Frequency response 5-51, 5-52 Full-wave rectifier 3-50 Gain 4-53, 5-50, 5-51 Gain-bandwidth product 5-51 Gates 6-45 Germanium 3-49 Giga 1-52 Graticule 10-44 Growth 2-55 Half-wave rectifier 3-50 Hertz 1-51 High-frequency cut-off 5-52 High-frequency roll-off 5-52 High-pass filter 8-47, 8-48, 8-51, 8-50, 8-56 Input resistance 5-50 Integrated circuits 5-48 Intruder alarm 6-53 Inversion 6-46 Inverter 6-46, 6-47 Inverting amplifier 5-52, 5-54 Inverting input 5-49 J-K bistable 6-48, 6-49 JFET 4-48 TEACH-IN 2011 – Topic Index

821. 56 Everyday Practical Electronics, September 2011 Teach-In 2011Kilo 1-52 Kitchen timer 7-50 L-C band-pass filter 8-49 L-C band-stop filter 8-49 LDR 2-51 LED 3-50, 3-51, 3-55 LED flasher 7-51 Light-dependent resistor 2-51 Light-emitting diode 3-50 Light-emitting diodes 3-51 Load 4-48, 4-50 Logic 6-44, 6-47 Logic 0 6-44 Logic 1 6-44 Logic gates 6-45, 6-46, 6-52 Low-frequency cut-off 5-52 Low-frequency roll-off 5-52 Low-pass filter 8-47, 8-48, 8-51, 8-50, 8-55 MOSFET 4-48 MSB 9-46 Matching 8-50 Mega 1-52 Micro 1-52 Mid-band 5-52 Milli 1-52 Monostable pulse generator 7-46 Most significant bit 9-46 Motor control circuit 4-53 Multimeters 10-42, 10-43 Multiples 1-52 Music 1-52 N-type material 3-48, 4-46 NAND logic 6-46, 6-47 NOT logic 6-46 NPN transistor 4-46, 4-47 Nano 1-52 Negative feedback 4-51, 5-51 Non-inverting amplifier 5-52 Non-inverting input 5-49 OR logic 6-45, 6-46, 6-47 Off state 6-44 Off time 1-53 Ohm 1-51, 2-51 Ohm’s Law 2-50, 2-56 On state 6-44 On time 1-53, 7-46 Operating point 4-50 Operational amplifier 5-48, 5-49 Oscillator 4-55, 5-56 Oscilloscope 10-44, 10-45 Output resistance 5-50 P-type material 3-48, 4-46 PCB 10-48 PNP transistor 4-46, 4-47 PRESET input 6-48, 6-49 Parallel plate capacitor 2-53 Periodic time 1-53 Phase shift 5-49 Photodiode 3-50 Pi-network 8-47 Polarising voltage 2-53 Potentiometer 2-51 Power gain 5-50, 8-50 Power supplies 1-54 Pre-set resistor 2-51 Printed circuit board 10-48 Pulse generator 7-46, 7-48 Pulse period 1-53 Pulse repetition frequency 1-53, 7-48 Pulse waveform 1-52, 1-53 Q-factor 8-50 Quantisation 9-46, 9-47 R-2R ladder DAC 9-48 RESET input 6-48 Ramp waveform 1-52 Ramp-type ADC 9-50, 9-51 Rats nest 10-51 Rectifier 3-50 Rectifier diode 3-49, 3-50 Rejector circuit 8-49 Resistor colour code 2-52 Resistors 2-51 Resolution 9-49 Resonance 8-49 Reverse bias 3-48 Ripple counter 6-53 Roll-off 5-52 SET input 6-48 Sallen and Key filter 8-50 Saturated switch 4-52 Sawtooth waveform 1-52 Schematic diagram 1-55 Second-order filter 8-56 Semiconductor 3-48 Signal diode 3-50 Signal diodes 3-49 Signals 1-51, 1-50 Silicon 3-49 Simulation 1-56 Sinking 7-45 Sourcing 7-45 Speech 1-52 Square wave generator 7-49 Sub-multiples 1-52 Successive approx. ADC 9-50 T-network 8-47 TTL 6-50 Temp.-sensitive resistor 2-51 Termination 8-50 Thermistor 2-51 Time constant 2-55 Timer circuit 7-47 Timing diagram 6-48, 6-49 Tolerance 2-51 Transfer characteristic 4-49 Transformers 3-50 Transistor amplifier 4-54 Transistor switch 4-51 Transistors 4-46 Triangle waveform 1-52 Trigger input 7-48 Unbalanced attenuator 8-47 Valves 5-57 Variable capacitor 2-53 Variable resistor 2-51 Virtual instrument 10-45 Virtual test 10-49 Volt 1-51, 2-51 Voltage follower 5-52, 5-53 Voltage gain 5-50, 5-51, 8-50 Voltage measurement 10-43, 10-44 Watt 1-51 Waveform measurement 10-45 Waveforms 1-52, 1-58 Zener diode 3-50, 3-51, 3-54

822. 50 http://www.handsontec.com www.handsontec.com LCD+Keyboard Shield 10-Segments LED Bar Display Ethernet Module Arduino Uno MicroSD Breakout Board WiFi Module 20x4 LCD Display Module Stepper Motor Driver PWM Motor Speed Controller Breakout Board Modules Integrated Circuits Discrete Parts Assembled Kits Connectors

Teach-In Electronics

More Related Content

Viewers also liked (19)

Similar to Teach-In Electronics (20)

Recently uploaded (20)

Teach-In Electronics