EEE305 Assignment-1.pdf

Assignment-1
The Temperature Box: An Introductory Control System Project

Objective
● Problem based learning approach
● To design and implementation of a close loop feedback
temperature control system
● Analogue and digital circuit implementation
● Compare and differentiate by LM35 and DS18B20

COMPONENTS OF THIS PROJECT
● Sensor LM35 and DS18B20
● Scale and shift circuit
● Relay
● LED
● DC source
● Arduino uno
● Resistor
● potentiometer

EQUATIONS AND CONVERSIONS
We get, Vs=0.975+0.0125Tf
Also, Tf= 70 degree F ; Vs=1.85V
Tf=85 degree F ; Vs=2.04V
Tf=95 degree F ; Vs=2.16V
Tc=70 degree C ; Tf= 21.11 degree F
Tc= 85 degree C ; Tf= 29.44 degree F
Tc= 95 degree C ; Tf= 35 degree F
We will put 0.5V and 4.5V at 85 and 95 degree F in scale and shift equation which is
Vt= α+βVs

SCALE AND SHIFT CIRCUIT FOR LM35
Voltage output at 29 degree (low) , Vs=29*0.01=0.29 volts
Voltage output at 35 degree (high) , Vs = 35*0.01=0.35 volts
Vt=0.5V at 29 degree celsius and Vt=4.5V at 35 degree celsius
We know, Vt= α+βVs
0.5=α+β0.29 ……..(1)
4.5=α+β0.35 ……..(2)
From equation (1) and (2) we get,
α= -18.83 and β= 66.67
Let , R=100K
R1=R/β=100/66.67=1.5K
R2=[-5*(R)]/α=[-5*(100)]/(-18.83)= 26.6K

COMPARISON CIRCUIT
● Scaled and shifted sensor voltage is compared
to the predetermined high and low
temperatures.
● A decision is made (using digital logic)
whether to open or close the relay and, hence,
turn the device off or on.
● VH denote the voltage corresponding to the
highest desired temperature and VL denote
voltage corresponding to the lowest desired
temperature.
● The decision is based on three rules
1. The relay is on if VT < VL < VH.
2. The relay is off if VT > VH > VL.
3. The relay state is unchanged if VL < VT < VH.

COMPARISON CIRCUIT
● The decision is based on three rules
1. The relay is on if VT < VL < VH.
2. The relay is off if VT > VH > VL.
3. The relay state is unchanged if VL <
VT <VH.

COMPARISON OF LM35
After scaling,
Input voltage at comparison circuit for 29 degree celsius = 0.29 volts
Input voltage at comparison circuit for 35 degree celsius = 0.35 volts
We know, Vt= α+βVs
VL=Vt= (-18.83)+(66.67*0.29)=0.5V
VH=Vt= (-18.83)+(66.67*0.35)=4.5V

ANALOGUE CONTROLLER (LM35)
● Use to measure precise centigrade temperature.
● It is rated to operate over a -55 degree celsius to
150 degree celsius temperature range.
● Output voltage increases 10mV per degree celsius
rise in temperature.
● Input voltage is from 4 volts to 30 volts.
● Consumes about 60 microamperes of current.
● Output voltages are linearly comparative to the
celsius temperature.

RELAY
● Activated for strong positive
voltage.
● Get pulls on the switch and the
circuit is completed for LED and
then shines.
● Pull goes away when voltage is
released.
● Switch remains in original
position when a little voltage is
given.

DIGITAL AND LOGIC IMPLEMENTATION
● Here we need to define two logical
functions:
A = Vt < Vh, B = Vt >Vl.
1.VT greater than VH Then A =
1 and B = 0
2. VT less than VL Then B = 1 and A = 0
3.VT between VH and VL then A = B

DIGITAL LOGIC
● Bulb will be ON if
VT≤VL<VH
● Bulb will be OFF if VT
≥VH>VL
● Bulb will be UNCHANGED
if VL<VT<VH
A
A B OUT PUT
0 0 Previous
State
0 1 Previous
State
1 0 Off
1 1 Not Possible

DIGITAL CONTROLLER LM35
ADC Value Calculation
For,
29 Degree Celsius (0.29V)
Val = (0.29 × 1023) ÷ 5 = 59.33 = 59 (Approximately)
For ,
1.The relay is on if Vt ≤ Vl < Vh [on]
2. The relay is off if Vt ≥ Vh > Vl [off]
3. State is unchanged if Vl < Vt < Vh

DIGITAL CONTROLLER DS18B20
ADC Value Calculation
For,
For ,
1.The relay is on if Vt ≤ Vl < Vh [on]
2. The relay is off if Vt ≥ Vh > Vl [off]
3. State is unchanged if Vl < Vt < Vh

Complete circuit with LM35 temperature
sensor

When temperature is 28°C i.e. VT<VL<VH
and Lamp turns On

When temperature is 32°C i.e. VL<VT<VH and Lamp
should remain like its previous state but it becomes off.

When temperature is 36°C i.e. VL<VH<VT and
Lamp become off

Complete circuit using DS18B20 temperature
sensor

Temperature increased but no voltage is
generating from DS18B20

ARDUINO CODE FOR LM35
int sensor = A0, relay = 7, adc_in=0;
float temp=0;
void setup () {
Serial.begin(9600);
pinMode(relay, OUTPUT);
}
void loop() {
adc_in=analogRead(sensor);
temp= ((adc_in*5000.0)/1023.0)/10.0;
Serial.println(temp);
}
if (temp >=35){
digitalWrite(relay, LOW);
Serial.println("Relay off");
}
if (temp <=30){
digitalWrite(relay, HIGH);
Serial.println("Relay on");
}
delay(1000);

ARDUINO CODE FOR DS18B20
ARDUINO CODE FOR
DS18B20
void loop(void)
{
sensors.requestTemperatures();
temp=sensors.getTempCByIndex(0);
Serial.println(" C ");
Serial.println(temp);
if (temp >=35){
digitalWrite(relay, LOW);
Serial.println("Relay off");
}
if (temp <=30){
digitalWrite(relay, HIGH);
Serial.println("Relay on");
}
delay(1000);
}

COST ALLOCATION AND COMPARISON
DIGITAL CONTROLLER LM35
● LM35 sensor- 140tk
● Voltage source- 110tk
● Arduino-950tk
● RESISTOR-16tk (8 pisces)
● NPN BJT-4tk
● LED-2tk
● Jumper wire-30tk
● Relay-30tk
Total cost : 1282tk
DIGITAL CONTROLLER DS18B20
● DS18B20 sensor-100tk
● Voltage source-110tk
● Arduino-950tk
● NPN BJT-4tk
● LED-2tk
● Relay-30tk
● Jumper wire-30tk
Total cost : 1226tk

REFERENCE
https://techshopbd.com/

Conclusion
From this project we can say that analog circuit system instantly stops while
VT> VL and we also say that Digital circuit is costly but more efficient.

EEE305 Assignment-1.pdf

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