Wireless energy meter monitoring with automated tariff calculation

ELECTRICAL AND ELECTRONICS ENGINEERING Page 1
CHAPTER 1
INTRODUCTION
Electricity is the driving force behind the development of any country. With the rapid increase in
residential, commercial and industrial consumer of electricity throughout the world, it has now become
imperative for utilities companies to device better, non intrusive, environmentally- safe techniques of
gauging utilities consumption, so that correct bills can be generated and invoiced. Traditionally,
electricity meter are installed on consumers premises and the consumption information is collected by
meter readings on their fortnightly or monthly visit to the premises. But energy meter reading is a
monotonous and expensive task. Now the meter reader people goes to each meter and take the meter
reading manually to issue the bill which will later be entered in the billing software for billing and
payment automation. If the manual meter reading and bill data entry process can be automated then it
would reduced the laborious task and financial wastage.” Wireless Energy meter Monitoring with
Automated Tariff Calculation” is a metering system that is to be used for data collecting from the meter
and processing the collector data for billing and other decision purposes. In this project we have
proposed an automatic meter reading system which is low cost, high performance, highest data rate, and
highest coverage area.

CHAPTER 2
BLOCK DIAGRAM
2.1 TRANSMITTERSECTION
Fig 2.1.1 Block Diagram of Transmitter Section
MICRO
CONTROLLER
RELAY
CRYSTAL
OSCILLATOR
RESET
METER PULSE
LCD DISPLAY
TRANSMITTER

2.2 RECIEVER SECTION
Fig 2.2.1 Block Diagram of Receiver Section
MICROCONTROLLER
RECIEVER
RESET
LCD DISPLAY
CRYSTAL OSCILLATOR

CHAPTER 3
COMPONENTS DESCRIPTION
3.1 ATmega 328(MICROCONTROLLER)
The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two
independent registers to be accessed in one single instruction executed in one clock cycle. The
resulting architecture is more code efficient while achieving throughputs up toten times faster
than conventional CISC microcontrollers. The ATmega32 provides the following features: 32K
bytes of In-System Programmable Flash Program memory with Read-While-Write capabilities,
1024 bytes EEPROM, 2Kbyte SRAM, 32 general purpose I/O lines, 32 general purpose working
registers, a JTAG interface for Boundary-scan, On-chip Debugging support and programming,
three flexible Timer/Counters with compare modes, Internal and External Interrupts, a serial
programmable USART, a byte oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC
with optional differential input stage with programmable gain (TQFP package only), a
programmable Watchdog Timer with Internal Oscillator, an SPI serial port, and six software
selectable power saving modes. The Idle mode stops the CPU while allowing the USART, Two-
wire interface, A/D Converter, SRAM, Timer/Counters, SPI port, and interrupt system to
continue functioning. The Power-down mode saves the register contents but freezes the
Oscillator, disabling all other chip functions until the next External Interrupt or Hardware Reset.
In Power-save mode, the Asynchronous Timer continues to run, allowing the user to maintain a
timer base while the rest of the device is sleeping. The ADC Noise Reduction mode stops the
CPU and all I/O modules except A synchronous Timer and ADC, to minimize switching noise
during ADC conversions. In Standby mode, the crystal/resonator Oscillator is running while the
rest of the device is sleeping. This allows very fast start-up combined with low-power
consumption. In Extended Standby mode, both the main Oscillator and the Asynchronous Timer
continue to run. The device is manufactured using Atmel’s high density nonvolatile memory
technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system
through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-

chip Boot program running on the AVR core. The boot program can use any interface to
download the application program in the Application Flash memory. Soft-ware in the Boot Flash
section will continue to run while the Application Flash section is updated, providing true Read-
While-Write operation. By combining an 8-bit RISC CPU with In-System Self-Programmable
Flash on a monolithic chip, the Atmel ATmega32 is a powerful microcontroller that provides a
highly-flexible and cost-effective solution to many embedded control applications. The
ATmega32 AVR is supported with a full suite of program and system development tools
including: C compilers, macro assemblers, program debugger/simulators, in-circuit emulators,
and evaluation kits.
Fig 3.1.1 ATmega 328 Microcontroller Pin out

3.1.1 Features
 High-performance, Low-power AVR 8-bit Microcontroller
 Advanced RISC Architecture
– 131 Powerful Instructions – Most Single-clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16 MHz
– On-chip 2-cycle Multiplier
 Nonvolatile Program and Data Memories
– 32K Bytes of In-System Self-Programmable Flash
Endurance: 10,000 Write/Erase Cycles
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program True Read-While-Write Operation
– 1024 Bytes EEPROM Endurance: 100,000 Write/Erase Cycles
– 2K Byte Internal SRAM
– Programming Lock for Software Security
 JTAG (IEEE std. 1149.1 Compliant) Interface
– Boundary-scan Capabilities According to the JTAG Standard
– Extensive On-chip Debug Support
– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG
Interface
 Peripheral Features
– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes
– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture
Mode
– Real Time Counter with Separate Oscillator
– Four PWM Channels
– 8-channel, 10-bit ADC
8 Single-ended Channels

7 Differential Channels in TQFP Package Only
2 Differential Channels with Programmable Gain at 1x, 10x, or 200x
– Byte-oriented Two-wire Serial Interface
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
 Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby
and Extended Standby
 I/O and Packages
– 32 Programmable I/O Lines
– 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF
 Operating Voltages
– 2.7 - 5.5V for ATmega32L
– 4.5 - 5.5V for ATmega32
 Speed Grades
– 0 - 8 MHz for ATmega32L
– 0 - 16 MHz for ATmega32
 Power Consumption at 1 MHz, 3V, 25C for ATmega32L
– Active: 1.1 mA
– Idle Mode: 0.35 mA
– Power-down Mode: < 1 μA

3.2 RF TRANSCEIVER
An RF module (radio frequency module) is a (usually) small electronic device used to transmit
and/or receive radio signals between two devices. In an embedded system it is often desirable to
communicate with another device wirelessly. This wireless communication may be
accomplished through optical communication or through radio frequency (RF) communication.
For many applications the medium of choice is RF since it does not require line of sight. RF
communications incorporate a transmitter and/or receiver.
RF modules are widely used in electronic design owing to the difficulty of designing radio
circuitry. Good electronic radio design is notoriously complex because of the sensitivity of radio
circuits and the accuracy of components and layouts required to achieve operation on a specific
frequency. In addition, reliable RF communication circuit requires careful monitoring of the
manufacturing process to ensure that the RF performance is not adversely affected. Finally, radio
circuits are usually subject to limits on radiated emissions, and require Conformance testing and
certification by a standardization organization such as ETSI or the U.S. Federal Communications
Commission (FCC). For these reasons, design engineers will often design a circuit for an
application which requires radio communication and then "drop in" a pre-made radio module
rather than attempt a discrete design, saving time and money on development.
RF modules are most often used in medium and low volume products for consumer applications
such as garage door openers, wireless alarm systems, industrial remote controls, smart sensor
applications, and wireless home automation systems. They are sometimes used to replace
older infra red communication designs as they have the advantage of not requiring line-of-sight
operation.
Several carrier frequencies are commonly used in commercially-available RF modules, including
those in the industrial, scientific and medical (ISM) radio bands such as 433.92 MHz, 915 MHz,
and 2400 MHz. These frequencies are used because of national and international regulations
governing the used of radio for communication. Short Range Devices may also use frequencies
available for unlicensed such as 315 MHz and 868 MHz.

3.2.1Types of RF modules
The term RF module can be applied to many different types, shapes and sizes of small electronic
sub assembly circuit board. It can also be applied to modules across a huge variation of
functionality and capability. RF modules typically incorporate a printed circuit board, transmit or
receive circuit, antenna, and serial interface for communication to the host processor.
Most standard, well known types are covered here:
 Transmitter module
 Receiver module
 Transceiver module
 System on a chip module
3.2.1.1 Transmitter modules
An RF transmitter module is a small PCB sub-assembly capable of transmitting a radio wave
and modulating that wave to carry data. Transmitter modules are usually implemented alongside
a micro controller which will provide data to the module which can be transmitted. RF
transmitters are usually subject to regulatory requirements which dictate the maximum
allowable transmitter power output, harmonics, and band edge requirements.
3.2.1.2 Receiver modules
An RF receiver module receives the modulated RF signal, and demodulates it. There are two
types of RF receiver modules: super heterodyne receivers and super-regenerative receivers.
Super-regenerative modules are usually low cost and low power designs using a series of
amplifiers to extract modulated data from a carrier wave. Super-regenerative modules are
generally imprecise as their frequency of operation varies considerably with temperature and
power supply voltage. Super heterodyne receivers have a performance advantage over super-
regenerative; they offer increased accuracy and stability over a large voltage and temperature

range. This stability comes from a fixed crystal design which in turn leads to a comparatively
more expensive product.
Fig 3.2.1.1 RF Transceiver Module

Fig 3.2.1.2 RF Transceiver Module

3.3 LCD DISPLAY
LCD stands for Liquid Crystal Display, which is used to shows status of an application,
display values, debugging a program, etc.,
3.3.1 Construction of Liquid crystal display
A Liquid crystal display is a passive device, which means it doesn’t produce any light to
display characters, images, video and animations. But it simply alters the light travelling through
it. The internal construction of LCD describes how the light altered when it passes through it in
order to produce any characters, images, etc.
Consider a single pixel area in LCD, in which there are two polarization filters oriented at
90 degree angle to each other as shown in figure 1.1. These filters are used to polarize the
unpolarized light. The first filter (Vertical polarized filter in figure 1.1) polarizes the light with
one polarization plane (Vertical). When the vertically polarized light passes through the second
filter (Horizontal polarized filter) no light output will produce.
Fig 3.3.1.1 Orientation of two polarization filters in LCD

The vertically polarized light should rotate 90 degrees in order to pass through the
horizontal polarized light. This can be achieving by embedding liquid crystal layer between two
polarization filters. The liquid crystal layer consists of rod shaped tiny molecules and ordering of
these molecules creates directional orientation property. These molecules in the liquid crystal are
twisted 90 degrees as shown in the figure 1.2. The vertically polarized light passes through
rotation of the molecules and twisted to 90 degrees. When the orientation of light matches with
the outer polarization filter light will pass it and brightens the screen.
Fig 3.3.1.2 Liquid Crystal molecules orientation.
If the Liquid crystal molecules are twisted 90 degrees more precisely, then more light
will pass through it. Two glass transparent electrodes are aligned front and back of the liquid
crystal in order to change the orientation of the crystal molecules by applying voltage between
them as shown in figure 1.3 and figure 1.4. If there is no voltage applied between the electrodes,
the orientation of molecules will remain twist at 90 degrees and the light passes through the outer
polarization filter thus pixel appears as complete white. If the voltage is applied large enough the
molecules in the liquid crystal layer changes its orientation (untwist) so that light orientation also
changes and then blocked by the outer polarization filter thus the pixel appears black. In this

way, black and white images or characters are produced. By arranging small pixels together as a
matrix will produce on which it is possible to show different sizes of images and characters. By
controlling the voltage applied between liquid crystal layers in each pixel, light can be allowed to
pass through outer polarization filter in various amounts, so that it can possible to produce
different gray levels on the LCD screen.
Generally the electrodes is made up of Indium Tin Oxide (ITO) which is
transparent material, hence it is simply called glass electrodes plates. LCD display is also
“twisted neumatic LCD” because of twist and untwist of molecules in liquid crystal layer.
Fig 3.3.1.3 LCD Display

Fig 3.3.1.4 Orientation of Liquid crystal molecules altered by applying voltage between two ITO
glass plates.

3.4 ENCODER(HT12E)
HT12E is a 212 series encoder IC widely used in remote control and very common among Radio
Frequency RF applications. This HT12E IC capable of converting 12 bit Parallel data inputs into
serial outputs. These bits are classified into 8 (A0-A7) address bits and 4(AD0-AD3) data bits.
Using the address pins we can provide 8 bit security code for secured data transmission between
the encoder and the decoder. The encoder and decoder should use the same address and data
format. HT12E is capable of operating in a wide Voltage range from 2.4V to 12V and also
consists of a built in oscillator. Let’s move into the working of HT12E encoder IC.
3.4.1 Pin Description of IC HT12E:
The pin Description of the IC HT12E was pretty simple to understand with total of 18 pins.
 VDD and VSS: Positive and negative power supply pins.
 OSC1 and OSC2: Input and output pins of the internal oscillator present inside the IC.
 TE: This pin is used for enabling the transmission, a low signal in this pin will enable the
transmission of data bits.

 A0 – A7: These are the input address pins used for secured transmission of this data.
Fig 3.4.1 Pin Diagram of HT12E
 These pins can be connected to VSS for low signal or left open for high state.
 AD0 – AD3: This pins are feeding data into the the IC. These pins may be connected to VSS
for sending LOW since it is a active low pin
 DOUT: The output of the encoder can be obtained through this pin and can be connected to
the RF transmitter.

3.4.2 Working of HT12E IC:
Fig 3.4.2 HT12E Transmission Timing
HT12E starts working with a low signal on the TE pin. After receiving a low signal the HT12E
starts the transmission of 4 data bits as shown in the timing diagram above. And the output cycle
will repeats based on the status of the TE pin in the IC. If the TE pin retains the low signal the
cycle repeats as long as the low signal in the TE pin exists. The encoder IC will be in standby
mode if the TE pin is disabled and thus the status of this pin was necessary for encoding process.
The address of these bits can be set through A0 – A7 and the same scheme should be used in
decoders to retrieve the signal bits.

3.4.3 Practical Circuit Using HT12E:
Fig 3.4.3 Circuit for HT12E

3.5 DECODER(HT12D)
HT12D is a decoder integrated circuit that belongs to 212 series of decoders. This series of
decoders are mainly used for remote control system applications, like burglar alarm, car door
controller, security system etc. It is mainly provided to interface RF and infrared circuits. They
are paired with 212 series of encoders. The chosen pair of encoder/decoder should have same
number of addresses and data format.
In simple terms, HT12D converts the serial input into parallel outputs. It decodes the serial
addresses and data received by, say, an RF receiver, into parallel data and sends them to output
data pins. The serial input data is compared with the local addresses three times continuously.
The input data code is decoded when no error or unmatched codes are found. A valid
transmission in indicated by a high signal at VT pin.
HT12D is capable of decoding 12 bits, of which 8 are address bits and 4 are data bits. The data
on 4 bit latch type output pins remain unchanged until new is received.

3.5.1 Pin description of HT12D
Pin
No
Function Name
1
8 bit Address pins for input
A0
2 A1
3 A2
4 A3
5 A4
6 A5
7 A6
8 A7
9 Ground (0V) Ground
10
4 bit Data/Address pins for output
D0
11 D1
12 D2
13 D3
14 Serial data input Input
15 Oscillator output Osc2
16 Oscillator input Osc1
17 Valid transmission; active high VT
18 Supply voltage; 5V (2.4V-12V) Vcc

Fig 3.5.1 Circuit for HT12D
 VDD and VSS are used to provide power to the IC, Positive and Negative of the power
supply respectively. As I said earlier its operating voltage can be in the range 2.4V to
12V
 OSC1 and OSC2 are used to connect external resistor for internal oscillator of HT12D.
OSC1 is the oscillator input pin and OSC2 is the oscillator output pin as shown in the
figure below.
Fig 3.5.2 Oscillator of HT12D

 A0 – A7 are the address input pins. Status of these pins should match with status of
address pin in HT12E (used in transmitter) to receive the data. These pins can be
connected to VSS or left open.
 DIN is the serial data input pin and can be connected to a RF receiver output.
 D8 – D11 are the data output pins. Status of these pins can be VSS or VDD depending
upon the received serial data through pin DIN.
 VT stand for Valid Transmission. This output pin will be HIGH when valid data is
available at D8 – D11 data output pins.
3.5.2 Working
Fig 3.5.3 HT12D Decoder Timing
HT12D decoder will be in standby mode initially ie, oscillator is disabled and a HIGH on DIN
pin activates the oscillator. Thus the oscillator will be active when the decoder receives data
transmitted by an encoder. The device starts decoding the input address and data. The decoder
matches the received address three times continuously with the local address given to pin A0 –
A7. If all matches, data bits are decoded and output pins D8 – D11 are activated. This valid data
is indicated by making the pin VT (Valid Transmission) HIGH. This will continue till the
address code becomes incorrect or no signal is received.

3.6 ARDUINO UNO BOARD
The Arduino Uno is a microcontroller board based on the ATmega328 (datasheet). It has 14
digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz
crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It
contains everything needed to support the microcontroller; simply connect it to a computer with
a USB cable or power it with a AC-to-DC adapter or battery to get started. The Uno differs from
all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it
features the Atmega8U2 programmed as a USB-to-serial converter. "Uno" means one in Italian
and is named to mark the upcoming release of Arduino 1.0. The Uno and version 1.0 will be the
reference versions of Arduno, moving forward. The Uno is the latest in a series of USB Arduino
boards, and the reference model for the Arduino platform.
3.6.1 Summary
Microcontroller ATmega328
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limits) 6-20V
Digital I/O Pins 14 (of which 6 provide PWM output)
Analog Input Pins 6
DC Current per I/O Pin 40 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 32 KB of which 0.5 KB used by
Boot loader
SRAM 2 KB
EEPROM 1 KB
Clock Speed 16 MHz

3.6.2 Power
The Arduino Uno can be powered via the USB connection or with an external power supply. The
power source is selected automatically. External (non-USB) power can come either from an AC-
to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-
positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and
Vin pin headers of the POWER connector. The board can operate on an external supply of 6 to
20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and
the board may be unstable. If using more than 12V, the voltage regulator may overheat and
damage the board. The recommended range is 7 to 12 volts. The power pins are as follows:
 VIN: The input voltage to the Arduino board when it's using an external power source (as
opposed to 5 volts from the USB connection or other regulated power source) . You can
supply voltage through this pin, or, if supplying voltage via the power jack, access it
through this pin.
 5V: The regulated power supply used to power the microcontroller and other components
on the board. This can come either from VIN via an on-board regulator, or be supplied by
USB or another regulated 5V supply.
 3V3: A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50
mA.
 GND: Ground pins.
3.6.3 Memory
The Atmega328 has 32 KB of flash memory for storing code (of which 0,5 KB is used for the
boot loader); It has also 2 KB of SRAM and 1 KB of EEPROM (which can be read and written
with the EEPROM library).

3.6.4 Input and Output
Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(),
digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or
receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of
20-50 kOhms. In addition, some pins have specialized functions:
 Serial: 0 (RX) and 1 (TX).
Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the
corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.
 External Interrupts: 2 and 3.
These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a
change in value. See the attachInterrupt() function for details.
 PWM: 3, 5, 6, 9, 10, and 11.
Provide 8-bit PWM output with the analogWrite() function.
 SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK).
These pins support SPI communication, which, although provided by the underlying hardware, is
not currently included in the Arduino language.
 LED: 13.
There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on,
when the pin is LOW, it's off.
The Uno has 6 analog inputs, each of which provides 10 bits of resolution (i.e. 1024 different
values). By default they measure from ground to 5 volts, though is it possible to change the
upper end of their range using the AREF pin and the
analogReference() function. Additionally, some pins have specialized functionality:
 I²C: 4 (SDA) and 5 (SCL).Support I²C (TWI) communication using the Wire library.
There are a couple of other pins on the board:
 AREF: Reference voltage for the analog inputs. Used with analogReference().
 Reset: Bring this line LOW to reset the microcontroller. Typically used to add a reset
button to shields which block the one on the board.

3.6.5 Communication
The Arduino Uno has a number of facilities for communicating with a computer, another
Arduino, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial
communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega8U2 on the
board channels this serial communication over USB and appears as a virtual com port to
software on the computer. The '8U2 firmware uses the standard USBCOM drivers, and no
external driver is needed. However, on Windows, an *.inf file is required. The Arduino software
includes a serial monitor which allows simple textual data to be sent to and from the Arduino
board. The RX and TX LEDs on the board will flash when data is being transmitted via the
USB-to-serial chip and USB connection to the computer (but not for serial communication on
pins 0 and 1).A SoftwareSerial library allows for serial communication on any of the Uno's
digital pins. The ATmega328 also support I2C (TWI) and SPI communication. The Arduino
software includes a Wirelibrary to simplify use of the I2Cbus.
3.6.6 Programming
The Arduino Uno can be programmed with the Arduino software (download). Select "Arduino
Uno w/ATmega328" from the Tools > Boardmenu (according to the microcontroller on your
board).The ATmega328 on the Arduino Uno comes preburned with a bootloader that allows us
to upload new code to it without the use of an external hardware programmer. It communicates
using the original STK500
Protocol (reference,C header files). We can also bypass the bootloader and program the
microcontroller through the ICSP (In-Circuit Serial Programming) header. The ATmega8U2
firmware source code is available. The ATmega8U2 is loaded with a DFU bootloader, which can
be activated by connecting the solder jumper on the back of the board (near the map of Italy) and
then resetting the 8U2. We can then use Atmel's FLIP software (Windows) or the DFU
programmer (Mac OS X and Linux) to load a new firmware. Or we can use the ISP header with
an external programmer (overwriting the DFU bootloader).

3.6.7 Automatic (Software) Reset
Rather than requiring a physical press of the reset button before an upload, the Arduino Uno is
designed in a way that allows it to be reset by software running on a connected computer. One of
the hardware flow control lines (DTR) of the ATmega8U2 is connected to the reset line of the
ATmega328 via a 100 nanofarad capacitor. When this line is asserted (taken low), the reset line
drops long enough to reset the chip. The Arduino software uses this capability to allow you to
upload code by simply pressing the upload button in the Arduino environment. This means that
the bootloader can have a shorter timeout, as the lowering of DTR can be well-coordinated with
the start of the upload. This setup has other implications. When the Uno is connected to either a
computer running Mac OS X or Linux, it resets each time a connection is made to it from
software (via USB). For the following half-second or so, the bootloader is running on the Uno.
While it is programmed to ignore malformed data (i.e. anything besides an upload of new code),
it will intercept the first few bytes of data sent to the board after a connection is opened. If a
sketch running on the board receives one-time configuration or other data when it first starts,
make sure that the software with which it communicates waits a second after opening the
connection and before sending this data. The Uno contains a trace that can be cut to disable the
auto-reset. The pads on either side of the trace can be soldered together to re-enable it. It's
labeled "RESET-EN". We may also be able to disable the auto-reset by connecting a 110 ohm
resistor from 5V to the reset line.
3.6.8 USB Overcurrent Protection
The Arduino Uno has a resettable poly fuse that protects your computer's USB ports from shorts
and overcurrent. Although most computers provide their own internal protection, the fuse
provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse
will automatically break the connection until the short or overload is removed.

3.6.9 Physical Characteristics
The maximum length and width of the Uno PCB are 2.7 and 2.1 inches respectively, with the
USB connector and power jack extending beyond the former dimension. Three screw holes allow
the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8
is 160 mil(0.16"), not an even multiple of the 100 mil spacing of the other pins.

3.7 BRIDGE RECTIFIER
A Full Wave Rectifier Circuit produces an output voltage or current which is purely DC or has
some specified DC component. Full wave rectifiers have some fundamental advantages over
their half wave rectifier counterparts. The average (DC) output voltage is higher than for half
wave, the output of the full wave rectifier has much less ripple than that of the half wave rectifier
producing a smoother output waveform.
In a Full Wave Rectifier circuit two diodes are now used, one for each half of the cycle. A
multiple winding transformer is used whose secondary winding is split equally into two halves
with a common centre tapped connection, (C). This configuration results in each diode
conducting in turn when its anode terminal is positive with respect to the transformer centre
point C producing an output during both half-cycles, twice that for the half wave rectifier so it is
100% efficient as shown below.
3.7.1 Full Wave Rectifier Circuit
Fig 3.7.1.1 Full wave Rectifier circuit

The full wave rectifier circuit consists of two power diodes connected to a single load resistance
(RL) with each diode taking it in turn to supply current to the load. When point A of the
transformer is positive with respect to point C, diode D1 conducts in the forward direction as
indicated by the arrows.
When point B is positive (in the negative half of the cycle) with respect to point C,
diode D2conducts in the forward direction and the current flowing through resistor R is in the
same direction for both half-cycles. As the output voltage across the resistor R is the phasor sum
of the two waveforms combined, this type of full wave rectifier circuit is also known as a “bi-
phase” circuit.
As the spaces between each half-wave developed by each diode is now being filled in by the
other diode the average DC output voltage across the load resistor is now double that of the
single half-wave rectifier circuit and is about 0.637Vmax of the peak voltage, assuming no
losses.
Where: VMAX is the maximum peak value in one half of the secondary winding and VRMS is the
rms value.
The peak voltage of the output waveform is the same as before for the half-wave rectifier
provided each half of the transformer windings have the same rms voltage value. To obtain a
different DC voltage output different transformer ratios can be used. The main disadvantage of
this type of full wave rectifier circuit is that a larger transformer for a given power output is
required with two separate but identical secondary windings making this type of full wave
rectifying circuit costly compared to the “Full Wave Bridge Rectifier” circuit equivalent.

3.7.2 The Full Wave Bridge Rectifier
Another type of circuit that produces the same output waveform as the full wave rectifier circuit
above, is that of the Full Wave Bridge Rectifier. This type of single phase rectifier uses four
individual rectifying diodes connected in a closed loop “bridge” configuration to produce the
desired output. The main advantage of this bridge circuit is that it does not require a special
centre tapped transformer, thereby reducing its size and cost. The single secondary winding is
connected to one side of the diode bridge network and the load to the other side as shown below.
3.7.3 The Diode Bridge Rectifier
Fig 3.7.3.1 Diode Bridge Rectifier
The four diodes labeled D1 to D4 are arranged in “series pairs” with only two diodes conducting
current during each half cycle. During the positive half cycle of the supply,
diodesD1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the current
flows through the load.

3.7.3.1 The Positive Half-cycle
Fig 3.7.3.1.1 Current flow through the load
During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but
diodes D1and D2 switch “OFF” as they are now reverse biased. The current flowing through the
load is the same direction as before.
3.7.3.2 The Negative Half-cycle
Fig 3.7.3.2.1 Current flow in Negative half cycle
As the current flowing through the load is unidirectional, so the voltage developed across the
load is also unidirectional the same as for the previous two diode full-wave rectifier, therefore
the average DC voltage across the load is 0.637Vmax.

Fig 3.7.3.2.2 Four pin Bridge Rectifier
3.7.4 Typical Bridge Rectifier
However in reality, during each half cycle the current flows through two diodes instead of just
one so the amplitude of the output voltage is two voltage drops ( 2 x 0.7 = 1.4V ) less than the
input VMAX amplitude. The ripple frequency is now twice the supply frequency (e.g. 100Hz for a
50Hz supply or 120Hz for a 60Hz supply.)
Although we can use four individual power diodes to make a full wave bridge rectifier, pre-made
bridge rectifier components are available “off-the-shelf” in a range of different voltage and
current sizes that can be soldered directly into a PCB circuit board or be connected by spade
connectors.
The image to the right shows a typical single phase bridge rectifier with one corner cut off. This
cut-off corner indicates that the terminal nearest to the corner is the positive or +ve output
terminal or lead with the opposite (diagonal) lead being the negative or -ve output lead. The
other two connecting leads are for the input alternating voltage from a transformer secondary
winding.

Fig 3.7.4.1 Bridge Rectifier

3.8 TRANSFORMER
Energy from one circuit to another without any direct electrical connection and with the help of
mutual induction between two windings. It transforms power from one circuit to another without
changing its frequency but may be in different voltage level.
This is a very short and simple definition of transformer.
3.8.1 Working Principle of Transformer
The working principle of transformer is very simple. It depends upon Faraday's law of
electromagnetic induction. Actually, mutual induction between two or more winding is
responsible for transformation action in an electrical transformer.
Faraday's Laws of Electromagnetic Induction
According to these Faraday's laws, "Rate of change of flux linkage with respect to time is
directly proportional to the induced EMF in a conductor or coil".
Basic Theory of Transformer
Say you have one winding which is supplied by an alternating electrical source. The alternating
current through the winding produces a continually changing flux or alternating flux that
surrounds the winding. If any other winding is brought nearer to the previous one, obviously
some portion of this flux will link with the second. As this flux is continually changing in its
amplitude and direction, there must be a change in flux linkage in the second winding or coil.
According to Faraday's law of electromagnetic induction, there must be an EMF induced in the
second. If the circuit of the later winding is closed, there must be an current flowing through it.
This is the simplest form of electrical power transformer and this is the most basic of working
principle of transformer. For better understanding, we are trying to repeat the above
explanation in a more brief way here. Whenever we apply alternating current to an electric coil,
there will be an alternating flux surrounding that coil. Now if we bring another coil near the first
one, there will be an alternating flux linkage with that second coil. As the flux is alternating,

there will be obviously a rate of change in flux linkage with respect to time in the second coil.
Naturally emf will be induced in it as per Faraday's law of electromagnetic induction. This is the
most basic concept of the theory of transformer. The winding which takes electrical power
from the source, is generally known as primary winding of transformer. Here in our above
example it is first winding. The winding which gives the desired output voltage due to mutual
induction in the transformer, is commonly known as secondary winding of transformer. Here in
our example it is second winding. The above mentioned form of transformer is theoretically
possible but not practically, because in open air very tiny portion of the flux of the first winding
will link with second; so the current that flows through the closed circuit of later, will be so small
in amount that it will be difficult to measure. The rate of change of flux linkage depends upon

the amount of linked flux with the second winding. So, it is desired to be linked to almost all flux
of primary winding to the secondary winding. This is effectively and efficiently done by placing
one low reluctance path common to both of the winding. This low reluctance path is core of
transformer, through which maximum number of flux produced by the primary is passed through
and linked with the secondary winding. This is the most basic theory of transformer.
Main Constructional Parts of Transformer
The three main parts of a transformer are,
1. Primary Winding of transformer - it produces magnetic flux when it is connected to
electrical source.
2. Magnetic Core of transformer - the magnetic flux produced by the primary winding, that
will pass through this low reluctance path linked with secondary winding and create a closed
magnetic circuit.
3. Secondary Winding of transformer - the flux, produced by primary winding, passes
through the core, will link with the secondary winding. This winding also wounds on the
same core and gives the desired output of the transformer.
Fig 3.8.1 Transformer

3.9 RESISTORS
A resistor is a passive two-terminal electrical component that implements electrical resistance as
a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage
levels within circuits. In electronic circuits, resistors are used to limit current flow, to adjust
signal levels, bias active elements, and terminate transmission lines among other uses. High-
power resistors, that can dissipate many watts of electrical power as heat, may be used as part of
motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have
resistances that only change slightly with temperature, time or operating voltage. Variable
resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or
as sensing devices for heat, light, humidity, force, or chemical activity.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous
in electronic equipment. Practical resistors as discrete components can be composed of various
compounds and forms. Resistors are also implemented within integrated circuits.
The electrical function of a resistor is specified by its resistance: common commercial resistors
are manufactured over a range of more than nine orders of magnitude. The nominal value of the
resistance will fall within a manufacturing tolerance.
3.9.1 Theory of operation

The hydraulic analogy compares electric current flowing through circuits to water flowing
through pipes. When a pipe (left) is filled with hair (right), it takes a larger pressure to achieve
the same flow of water. Pushing electric current through a large resistance is like pushing water
through a pipe clogged with hair: It requires a larger push (voltage drop) to drive the same flow
(electric current).
3.9.2 Ohm's law
The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law:
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the
constant of proportionality is the resistance (R). For example, if a 300 ohm resistor is attached
across the terminals of a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through
that resistor.
Practical resistors also have some inductance and capacitance which will also affect the relation
between voltage and current in alternating current circuits.
The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An
ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a
very large range of values, the derived units of milliohm (1 mΩ = 10−3 Ω), kilohm (1 kΩ =
103Ω), and megohm (1 MΩ = 106 Ω) are also in common usage.
3.9.3 Series and parallel resistors
The total resistance of resistors connected in series is the sum of their individual resistance
values.

The total resistance of resistors connected in parallel is the reciprocal of the sum of
the reciprocals of the individual resistors.
So, for example, a 10 ohm resistor connected in parallel with a 5 ohm resistor and a 15 ohm
resistor will produce the inverse of 1/10+1/5+1/15 ohms of resistance, or 1/(.1+.2+.067)=2.725
ohms.
A resistor network that is a combination of parallel and series connections can be broken up into
smaller parts that are either one or the other. Some complex networks of resistors cannot be
resolved in this manner, requiring more sophisticated circuit analysis. Generally, the Y-Δ
transform, or matrix methods can be used to solve such problems.
3.9.4 Power dissipation
At any instant, the power P (watts) consumed by a resistor of resistance R (ohms) is calculated
as: where V (volts) is the voltage across the resistor and I (amps) is
the current flowing through it. Using Ohm's law, the two other forms can be derived. This power
is converted into heat which must be dissipated by the resistor's package before its temperature
rises excessively.
Resistors are rated according to their maximum power dissipation. Discrete resistors in solid-
state electronic systems are typically rated as 1/10, 1/8, or 1/4 watt. They usually absorb much
less than a watt of electrical power and require little attention to their power rating.

Fig3.9.4.1 An aluminium-housed power resistor rated for 50 W when heat-sinked
Resistors required to dissipate substantial amounts of power, particularly used in power supplies,
power conversion circuits, and power amplifiers, are generally referred to as power resistors; this
designation is loosely applied to resistors with power ratings of 1 watt or greater. Power resistors
are physically larger and may not use the preferred values, color codes, and external packages
described below.
If the average power dissipated by a resistor is more than its power rating, damage to the resistor
may occur, permanently altering its resistance; this is distinct from the reversible change in
resistance due to its temperature coefficient when it warms. Excessive power dissipation may
raise the temperature of the resistor to a point where it can burn the circuit board or adjacent
components, or even cause a fire. There are flameproof resistors that fail (open circuit) before
they overheat dangerously.
Since poor air circulation, high altitude, or high operating temperatures may occur, resistors may
be specified with higher rated dissipation than will be experienced in service.
All resistors have a maximum voltage rating; this may limit the power dissipation for higher
resistance values.

3.10 CAPACITORS
A capacitor (originally known as a condenser) is a passive two-terminal electrical
component used to store electrical energy temporarily in an electric field. The forms of practical
capacitors vary widely, but all contain at least two electrical conductors (plates) separated by
a dielectric (i.e. an insulator that can store energy by becoming polarized). The conductors can be
thin films, foils or sintered beads of metal or conductive electrolyte, etc. The non conducting
dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics
include glass, ceramic, plastic film, air, vacuum, paper, mica, and oxide layers. Capacitors are
widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor,
an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of
an electrostatic field between its plates.
When there is a potential difference across the conductors (e.g., when a capacitor is attached
across a battery), an electric field develops across the dielectric, causing positive charge +Q to
collect on one plate and negative charge −Q to collect on the other plate. If a battery has been
attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor.
However, if a time-varying voltage is applied across the leads of the capacitor, a displacement
current can flow.
An ideal capacitor is characterized by a single constant value, its capacitance. Capacitance is
defined as the ratio of the electric charge Q on each conductor to the potential
difference V between them. The SI unit of capacitance is the farad (F), which is equal to
one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to
about 1 mF (10−3 F).
The larger the surface area of the "plates" (conductors) and the narrower the gap between them,
the greater the capacitance is. In practice, the dielectric between the plates passes a small amount
of leakage current and also has an electric field strength limit, known as the breakdown voltage.
The conductors and leads introduce an undesired inductance and resistance.
Capacitors are widely used in electronic circuits for blocking direct current while
allowing alternating current to pass. In analog filter networks, they smooth the output of power

supplies. In resonant circuits they tune radios to particular frequencies. In electric power
transmission systems, they stabilize voltage and power flow.
Fig 3.10.1 Capacitors

3.11 TRANSISTORS
A transistor is a device that regulates current or voltage flow and acts as a switch or gate for
electronic signals. Transistors consist of three layers of a semiconductor material, each capable
of carrying a current.
The transistor was invented by three scientists at the Bell Laboratories in 1947, and it rapidly
replaced the vacuum tube as an electronic signal regulator. A transistor regulates current or
voltage flow and acts as a switch or gate for electronic signals. A transistor consists of three
layers of a semiconductor material, each capable of carrying a current. A semiconductor is a
material such as germanium and silicon that conducts electricity in a "semi-enthusiastic" way. It's
somewhere between a real conductor such as copper and an insulator (like the plastic wrapped
around wires).
The semiconductor material is given special properties by a chemical process called doping. The
doping results in a material that either adds extra electrons to the material (which is then
called N-type for the extra negative charge carriers) or creates "holes" in the material's crystal
structure (which is then called P-type because it results in more positive charge carriers) . The
transistor's three-layer structure contains an N-type semiconductor layer sandwiched between P-
type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN
configuration).
A small change in the current or voltage at the inner semiconductor layer (which acts as the
control electrode) produces a large, rapid change in the current passing through the entire
component. The component can thus act as a switch, opening and closing an electronic gate
many times per second. Today's computers use circuitry made with complementary metal oxide
semiconductor (CMOS) technology. CMOS uses two complementary transistors per gate (one
with N-type material; the other with P-type material). When one transistor is maintaining a logic
state, it requires almost no power.

Transistors are the basic elements in integrated circuits (IC), which consist of very large numbers
of transistors interconnected with circuitry and baked into a single silicon microchip.
Fig 3.11.1 Transistors

3.12 RELAY
A relay is an electrically operated switch. Many relays use an electromagnet to mechanically
operate a switch, but other operating principles are also used, such as solid-state relays. Relays
are used where it is necessary to control a circuit by a low-power signal (with complete electrical
isolation between control and controlled circuits), or where several circuits must be controlled by
one signal. The first relays were used in long distance telegraph circuits as amplifiers: they
repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays
were used extensively in telephone exchanges and early computers to perform logical operations.
Fig 3.12.1 Relay
A type of relay that can handle the high power required to directly control an electric motor or
other loads is called a contactor. Solid-state relays control power circuits with no moving parts,
instead using a semiconductor device to perform switching. Relays with calibrated operating
characteristics and sometimes multiple operating coils are used to protect electrical circuits from

overload or faults; in modern electric power systems these functions are performed by digital
instruments still called "protective relays".
Magnetic latching relays require one pulse of coil power to move their contacts in one direction,
and another, redirected pulse to move them back. Repeated pulses from the same input have no
effect. Magnetic latching relays are useful in applications where interrupted power should not be
able to transition the contacts.
Magnetic latching relays can have either single or dual coils. On a single coil device, the relay
will operate in one direction when power is applied with one polarity, and will reset when the
polarity is reversed. On a dual coil device, when polarized voltage is applied to the reset coil the
contacts will transition. AC controlled magnetic latch relays have single coils that employ
steering diodes to differentiate between operate and reset commands.
A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron
yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one
or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke
and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so
that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition,
one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other
relays may have more or fewer sets of contacts depending on their function. The relay in the
picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit
between the moving contacts on the armature, and the circuit track on the printed circuit
board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that activates the
armature, and the consequent movement of the movable contact (s) either makes or breaks
(depending upon construction) a connection with a fixed contact. If the set of contacts was closed
when the relay was de-energized, then the movement opens the contacts and breaks the
connection, and vice versa if the contacts were open. When the current to the coil is switched off,
the armature is returned by a force, approximately half as strong as the magnetic force, to its
relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in
industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage
application this reduces noise; in a high voltage or current application it reduces arcing.

When the coil is energized with direct current, a diode is often placed across the coil to dissipate
the energy from the collapsing magnetic field at deactivation, which would otherwise generate
a voltage spike dangerous to semiconductor circuit components. Such diodes were not widely
used before the application of transistors as relay drivers, but soon became ubiquitous as
early germanium transistors were easily destroyed by this surge. Some automotive relays include
a diode inside the relay case.
If the relay is driving a large, or especially a reactive load, there may be a similar problem of
surge currents around the relay output contacts. In this case a snubber circuit (a capacitor and
resistor in series) across the contacts may absorb the surge. Suitably rated capacitors and the
associated resistor are sold as a single packaged component for this commonplace use.
If the coil is designed to be energized with alternating current (AC), some method is used to split
the flux into two out-of-phase components which add together, increasing the minimum pull on
the armature during the AC cycle. Typically this is done with a small copper "shading ring"
crimped around a portion of the core that creates the delayed, out-of-phase component,[9] which
holds the contacts during the zero crossings of the control voltage.

3.13 ELECTRONIC ENERGYMETER
Energy meter or watt-hour meter or is an electrical instrument that measures the amount of
electrical energy used by the consumers. Utilities is one of the electrical departments, which
install these instruments at every place like homes, industries, organizations, commercial
buildings to charge for the electricity consumption by loads such as lights, fans, refrigerator
and other home appliances
Fig 3.13.1 Electronic energy meter
The basic unit of power is watts and it is measured by using a watt meter. One thousand watts
make one kilowatt. If one uses one kilowatt in one hour duration, one unit of energy gets
consumed. So energy meters measure the rapid voltage and currents, calculate their product and
give instantaneous power. This power is integrated over a time interval, which gives the energy
utilized over that time period.
3.13.1 Two Basic Types of Watt-Hour Meter
The energy meters are classified into two basic categories, such as:
o Electromechanical Type Induction Meter
o Electronic Energy Meter

Watt hour meters are classified into two types by taking the following factors into
considerations:
o Types of displays analog or digital electric meter.
o Types of metering points: secondary transmission, grid, local and primary distribution.
o End applications like commercial, industrial and domestic purpose
o Technical aspects like single phases, three phases, High Tension (HT), Low Tension (LT) and
accuracy class materials.
The electricity supply connection may be either single phase or three phase depending on the
supply utilized by the domestic or commercial installations. Particularly in this article we are
going to study about the working principles of single-phase electromechanical induction type
watt- hour meter and also about three-phase electronic watt hour meter from the explanation of
two basic energy meters as described below .
3.13.2 Single Phase Electromechanical Induction Watt Hour Meter
It is a well-known and most common type of age-old watt-hour meter. It comprises a rotating
aluminum disc placed on a spindle between two electromagnets. The rotation speed of the disc is
proportional to the power, and this power is integrated by the use of gear trains and counter
mechanism. It is made of two silicon steel laminated electromagnets: shunt and series magnets.
Series magnet carries a coil which is of a few turns of thickness wire connected in series with the
line; whereas the shunt magnet carries a coil with numerous turns of thin wire connected across
the supply.
Braking magnet is a kind of permanent magnet that applies the force opposite to the normal disc
rotation to move that disc a balanced position and to stop the disc while power gets off.

Fig 3.13.2.1 Single Phase Electromechanical Induction Energy Meter
Series magnet produces a flux which is proportional to the flowing current, and shunt magnet
produces a flux proportional to the voltage. These two fluxes lag at 90 degrees due to inductive
nature. The interface of these two fields produces eddy current in the disk, utilizing a force,
which is proportional to the product of instantaneous voltage, current and the phase-angle
between them. A braking magnet is placed over one side of the disc, which produces a break
torque on the disc by a constant field provided by using a permanent magnet. Whenever
the braking and driving torques become equal, the speed of the disc becomes steady.
A Shaft or vertical spindle of the aluminum disc is associated with the gear arrangement that
records a number proportional to the revolutions of the disc. This gear arrangement sets the
number in a series of dials and indicates energy consumed over a time.
This type of energy meter is simple in construction and the accuracy is somewhat less due to
creeping and other external fields. A foremost problem with these types of energy meters is their
proneness to tampering, which necessitate an electrical-energy-monitoring system. These series
and shunt type meters are widely used in domestic and industrial applications.
Electronic energy meters are accurate, precise and reliable type of measuring instruments when
compared to electromechanical induction type meters. When connected to loads, they consume
less power and start measuring instantaneous. So, electronic type of three phase energy meter is
explained below with its working principle.

3.13.3 3-Phase Electronic Watt Hour Meter
This meter is able to perform current, voltage and power measurements in three phase supply
systems. By using these three phase meters, it is also possible to measure high voltages and
currents by using appropriate transducers. One of the types of three phase energy meters is
shown below (given as an example) that ensures reliable and accurate energy measurement
compared to the electromechanical meters.
Fig 3.13.3.1 Three Phase Watt Hour Meter
It uses AD7755, a single-phase energy measurement IC to acquire and process the input voltage
and current parameters. The voltage and currents of the power line are rated down to signal level
using transducers like voltage and current transformers and given to that IC as shown in figure.
These signals are sampled and converted into digital, multiplied by one another to get the
instantaneous power. Later these digital outputs are converted to frequency to drive an
electromechanical counter. The frequency rate of the output pulse is proportional to the
instantaneous power, and (in a given interval) it gives energy transfers to the load for a particular
number of pulses.

The microcontroller accepts the inputs from all the three energy measurement ICs for three phase
energy measurement and serves as the brain of the system by performing all the necessary
operations like: storing and retrieving data from EEPROM, operating the meter using buttons to
view energy consumption, calibrating phases and clearing readings; and, it also drives the
display using decoder IC.
Till now we have read about the energy meters and their working principles. For a deeper
understanding of this concept, the following description about the watt hour meter gives
complete circuit details and its connections using a microcontroller.

3.14 LIGHT DEPENDENTRESISTOR
A Light Dependent Resistor (LDR) or a photo resistor is a device whose resistivity is a function
of the incident electromagnetic radiation. Hence, they are light sensitive devices. They are also
called as photo conductors, photo conductive cells or simply photocells. They are made up of
semiconductor materials having high resistance. There are many different symbols used to
indicate a LDR, one of the most commonly used symbol is shown in the figure below. The arrow
indicates light falling on it.
Fig3.14.1 Representation of LDR
3.14.1 Working Principle of LDR
A light dependent resistor works on the principle of photo conductivity. Photo conductivity is
an optical phenomenon in which the materials conductivity is increased when light is absorbed
by the material. When light falls i.e. when the photons fall on the device, the electrons in the
valence band of the semiconductor material are excited to the conduction band. These photons in
the incident light should have energy greater than the band gap of the semiconductor material to
make the electrons jump from the valence band to the conduction band. Hence when light having
enough energy strikes on the device, more and more electrons are excited to the conduction band
which results in large number of charge carriers. The result of this process is more and more
current starts flowing through the device when the circuit is closed and hence it is said that the

resistance of the device has been decreased. This is the most common working principle of
LDR
3.14.2 Characteristics of LDR
LDR’s are light dependent devices whose resistance is decreased when light falls on them and
that is increased in the dark. When a light dependent resistor is kept in dark, its resistance is
very high. This resistance is called as dark resistance. It can be as high as 1012 Ω and if the
device is allowed to absorb light its resistance will be decreased drastically. If a constant voltage
is applied to it and intensity of light is increased the current starts increasing. Figure below
shows resistance vs. illumination curve for a particular LDR.
Fig 3.14.2.1 Characteristics curve for LDR
Photocells or LDR’s are non linear devices. There sensitivity varies with the wavelength of light
incident on them. Some photocells might not at all response to a certain range of wavelengths.
Based on the material used different cells have different spectral response curves. When light is
incident on a photocell it usually takes about 8 to 12ms for the change in resistance to take place,
while it takes one or more seconds for the resistance to rise back again to its initial value after
removal of light. This phenomenon is called as resistance recovery rate. This property is used in
audio compressors. Also, LDR’s are less sensitive than photo diodes and photo transistor. (A
photo diode and a photocell (LDR) are not the same, a photo-diode is a p-n junction
semiconductor device that converts light to electricity, whereas a photocell is a passive device,

there is no p-n junction in this nor it “converts” light to electricity). Types of Light Dependent
Resistors: Based on the materials used they are classified as: i) Intrinsic photo resistors (Un
doped semiconductor): These are made of pure semiconductor materials such as silicon or
germanium. Electrons get excited from valance band to conduction band when photons of
enough energy fall on it and number charge carriers is increased. ii) Extrinsic photo resistors:
These are semiconductor materials doped with impurities which are called as dopants. These
dopants create new energy bands above the valence band which are filled with electrons. Hence
this reduces the band gap and less energy is required in exciting them. Extrinsic photo resistors
are generally used for long wavelengths.
3.14.3 Construction of a Photocell
The structure of a light dependent resistor consists of a light sensitive material which is deposited
on an insulating substrate such as ceramic. The material is deposited in zigzag pattern in order to
obtain the desired resistance & power rating. This zigzag area separates the metal deposited areas
into two regions. Then the ohmic contacts are made on the either sides of the area. The
resistances of these contacts should be as less as possible to make sure that the resistance mainly
changes due to the effect of light only. Materials normally used are cadmium sulphide , cadmium
selenide, indium antimonide and cadmium sulphonide. The use of lead and cadmium is avoided
as they are harmful to the environment.

3.14.4 Applications of LDR
LDR’s have low cost and simple structure. They are often used as light sensors. They are used
when there is a need to detect absences or presences of light like in a camera light meter. Used in
street lamps, alarm clock, burglar alarm circuits, light intensity meters, for counting the packages
moving on a conveyor belt, etc.
Fig 3.14.4.1 LDR

3.15 VOLTAGE REGULATOR (7805)
The 78xx (sometimes L78xx, LM78xx, MC78xx….) is a family of self-contained fixed linear
voltage regulator integrated circuits. The 78xx family is commonly used in electronic circuits
requiring a regulated power supply due to their ease-of-use and low cost. For ICs within the
family, the xx is replaced with two digits, indicating the output voltage (for example, the 7805
has a 5 volt output, while the 7812 produces 12 volts). The 78xx line are positive voltage
regulators, they produce a voltage that a positive relative to a common ground. There is a related
line of 79xx devices which are complementary negative voltage regulators. 78xx and 79xx ICs
can be used in combination to provide positive and negative supply voltages in the same circuit.
Fig 3.15.1 Pin out of 7805 Regulator
3.15.1 Advantages
78xx series ICs do not require additional components to provide a constant, regulated source of
power, making them easy to use, as well as economical and efficient uses of space. Other voltage
regulators may require additional components to set the output voltage level, or to assist in the
regulation process. Some other designs (such as a switched-mode power supply) may need
substantial engineering expertise to implement.

3.15.2 Disadvantage
The input voltage must always be higher than the output voltage by some minimum amount
(typically 2.5 volts). This can make these devices unsuitable for powering some devices from
certain types of power sources(for example, powering a circuit that requires 5 volts using 6 volts
batteries will not work using a 7805)

CHAPTER 4
WORKING
4.1 TRANSMITTER SECTION
Fig 4.1.1 Block diagram for Transmitting section
ENERGY
METER
RF
TRANSMITTER
LCD DISPLAY
ARDUINO UNO-ATMEGA
328 INTERFACED BOARD

4.2 RECEIVER SECTION
Fig 4.2.1 Block Diagram for Receiver Section
RF RECIEVER
ARDUINO UNO- ATMEGA328
INTERFACED BOARD
LCD DISPLAY

CHAPTER 5
CIRCUIT DIAGRAM
5.1 TRANSMITTERSECTION
Fig 5.1.1 Circuit diagram for Transmitter Section

5.1.1 Description
The transmitter section consists of a RF Transmitting module, an energy meter, a LCD display
and an Arduino UNO board. The Arduino UNO board used here is a base for the
microcontroller, ATmega 328.
The energy meter pulse is taken out by using a LDR and is given as an input to the 10th pin of an
encoder IC HT12E. (10-13) pins are called DATA pins, in which the input data can be given to
any one of these four pins. The pin from 1 to 9 in HT12E IC is grounded, where 1 to 8 pins are
called ADDRESS pins.
The 15th and 16th pin is shorted by a 750kΩ resistance. So we connect one 680kΩ, three 22kΩ
and three 1kΩ resistors in series to obtain a resistance value of 750kΩ. The Vcc(5V) is given to
the encoder IC through the 18th pin. The output of the encoder IC will be a signal which is
modulated as well as encoded in the proper way for transmission.
The output from the IC HT12E is given to the DATA pin of the RF Transmitter module. The RF
Transmitter module consists of 4 pins in total, a GND pin, a DATA pin, a Vcc pin and an ANT
(antenna). The GND pin is grounded and a 5V is fed to the Vcc pin. The other fourth pin will
acts as an antenna.
The transmitter section here is the consumer’s house. So inorder to display the meter reading and
cost of consumption , a part of the output from the IC HT12E is taken out and given to an
Arduino UNO board.
An Arduino UNO board is a platform which comprises of the microcontroller ATmega 328,
programmer, reset pin and various other controllers which is used to operate the UNO board. The
program for what to display and how to display in the LCD is given to the microcontroller
(ATmega 328) which is inbuilt within the UNO board.
The program used here is the C programming which has been buildup using a programmer called
Arduino Software. The C program is installed into the microcontroller within the Arduino board
which consists of a programmer along with the board to convert the given C language to the
controller’s language. According to the command given, the Arduino board sends signal to the
LCD to display the rate and cost of consumption to the consumer.

5.2 RECEIVER SECTION
Fig 5.2.1 Circuit diagram for Receiver Section

5.2.1 Description
The Receiver section consists of a RF Receiver module, IC HT12D decoder, an Arduino UNO
board and a LCD. The transmitted data from the transmitter section is received in the receiver
section through an antenna. The RF Receiver module present here has 8 pins, in which 3 are
GND, 2 pins are DATA and one is ANT (antenna). The output is taken out from the DATA pin
and it is given to the decoder IC HT12D.
HT12D is the decoder IC. It has 18 pins in total, in which (1-8)pins are called the ADDRESS
pins, (10-13) are DATA pins, 14th pin is the DATAIN (DIN) pin, 15 and 16th pins are shorted
with a resistance off 33kΩ and 18th pin is the Vcc. The pins from 1 to 9 are grounded.
Now the 14th pin of IC HT12D will input the data from the RF Receiver module. The decoder
will decodes and unmodulate the signals received. These unmodulated signals are taken out
through the 17th pin to the Arduino UNO board.
The Arduino UNO board will receives the data (signal) from the decoder IC and displays the rate
and units consumed by the consumer in the LCD as explained in the transmitter section.
The hand held device as well as the LCD is placed in the Electricity Department (KSEB). So that
the authority could analyze the consumption and rate of consumption of each and every
consumer without any error in less time.

CHAPTER 6
PROGRAMMING CODE
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
#include <SoftwareSerial.h>
#define LCDtxPin 2
SoftwareSerial LCD = SoftwareSerial(2,LCDtxPin);
const int buttonPin = 7;
int buttonPushCounter = 0;
int buttonState = 0;
int lastButtonState = 0;
float rate = 0;
float rate1 = 0;
float unit=0;
float unit1=0;
int buttonState1 = 0;
void setup() {
LCD.begin(9600);
lcd.begin(16, 2);
pinMode(LCDtxPin, OUTPUT);
pinMode(buttonPin, INPUT);
Serial.begin(9600);
}

void loop() {
buttonState = digitalRead(buttonPin);
if (buttonState != lastButtonState) {
if (buttonState == HIGH ) {
buttonPushCounter++;
Serial.println("on");
Serial.print("number of button pushes: ");
Serial.println(buttonPushCounter);
} else {
Serial.println("off");
}
delay(50);
}
unit=buttonPushCounter*1;
unit1=unit/1000;
rate=buttonPushCounter*7;
rate1=rate/1000;
Serial.println("rate");
Serial.println(rate1);
Serial.println("unit");
Serial.println(unit1);
lcd.setCursor(0, 0);
lcd.print("YOUR CONSUMPTION");
delay(50);
lcd.setCursor(0, 4);

lcd.print("Rs:");
lcd.print(rate1);
lcd.print("UNIT:");
lcd.print(unit1);
delay(50);
lastButtonState = buttonState;
}

CHAPTER 7
APPLICATIONS
The wireless energy meter design in this project could find application in every state distribution
company for reading energy consumption. It can also be extended for metering and monitoring
other utility commodities, such as internet access, wireless drinking water consumption reading
etc.
5.1 ADVANTAGES
 Accurate meter reading, no more estimates
 Improved billing
 Accurate profile classes and measurement classes, true cost applied
 Improved security and tamper detection for equipment
 Energy management through profile data graphs
 Less financial burden correcting mistakes
 Less accrued expenditure
5.2 DISADVANTAGES
 Cause malfunction due to interference with other RF devices
 Higher electrical power drive.

CHAPTER 8
FUTURE SCOPE
The Wireless energy meter for India has the potential to change the future of the energy
billing system. It could help the energy distribution companies reduce cost and increase
profits, improve billing accuracy and efficiency, and contribute to the energy
sustainability! The wireless energy meter reading method used here can be replaced with
GSM modems and can be extended to make the energy billing system more widespread
and make it one system for the entire state.
The mode of payment by the consumers can be extended to credit cards, internet based
payments, ATM centers etc. This makes the wireless energy meter system simpler and
eliminating the need for customers to go to the recharge centers allowing the user
anytime recharge.

CHAPTER 9
ESTIMATION AND COSTING
COMPONENTS RANGE QUANTITY PRICE (RS)
ARUINO UNO
BOARD
- 2 1800
ADAPTER FOR
UNO BOARD
- 2 400
LCD DISPLAY 16 Chr X 2 Line 2 500
TRANSFORMER 12-0-12V1A 1 200
TRANSISTOR BC549 2 50
RESISTOR 680KΩ 1 25
RESISTOR 22KΩ 3 30
RESISTOR 33KΩ 1 15
RESISTOR 1KΩ 3 15
CAPACITOR 1000µF 1 10
RELAY 12V 1 75
LDR - 1 20
ENERGY METER - 1 850
PCB BOARD - 2 40
ENERGY METER
BOARD
- 1 100
2PIN AC CHORD - 1 125
BRIDGE
RECTIFIER
- 1 40
RF TRANCEIVER
MODULE
434MHz 1 475
18 PIN IC HT12E - 1 25

18 PIN IC HT12D - 1 25
7805 VOLTAGE
REGULATOR
- 1 15
COMPONENTS COST 5000
TRAVELLING EXPENCES 2500
PROGRAMMING STUDY 7000
TOTAL 14,500
Tab 9.1 Estimation and costing

CHAPTER 10
CONCLUSION
The present system is used for meter reading for electricity using RF Communication.
The system can be further modified to detect power theft between pole and individual
subscribers by installing the units at each subscriber end. For the readings of electricity
meters in the consumer premises to be transmitted to a central base station for further
processing billing etc. With tens of millions of meters to be read periodically and
regularly, this alone represents an enormous market. The cost of one system is on higher
side but if more number of systems are produced, and then the cost of mass production
will get reduced. The present system is implemented to send non voice data only. The
system can be further developed to transfer voice data through RF. But the system should
be robust enough to handle interference in the RF.

CHAPTER 11
BIBILIOGRAPHY
1. Loss. P.V.A, Lamego.M.M and Vieira.J.L.F,1998. A single phase microcontroller
based energy meter, IEEE Instrumentation and Measurements
2.Saptarshi De, Rahul Anand, A Naveen and Sirat Moinuddin, 2003. E-Metering Solution
for checking energy thefts and stearmlining revenue collection in INDIA,IEEE
3. Krzysztof Iniewski,2008. Wireless Technologies, CRC Press.

Wireless energy meter monitoring with automated tariff calculation

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