This document describes a student project to design and implement an analog and digital temperature control system using two temperature sensors - the LM35 and DS18B20. It includes the components, block diagrams, equations to convert between Celsius and Fahrenheit temperatures, and circuits to scale and shift the sensor output voltages. The digital system uses an Arduino to take ADC readings and control a relay based on predetermined high and low temperatures. While the analog LM35 circuit works as expected, issues were found with the DS18B20 circuit. Overall, the digital controller is more expensive but more efficient than the analog implementation.

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

2. 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

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

4. BLOCK DIAGRAM

5. 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

6. 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

7. Scale and Shift circuit

8. 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.

9. 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.

10. 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

11. 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.

12. 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.

13. 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

14. 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

15. DIGITAL CONTROLLER LM35
ADC Value Calculation
For,
29 Degree Celsius (0.29V)
Val = (0.29 × 1023) ÷ 5 = 59.33 = 59 (Approximately)
For ,
35 Degree Celsius (0.35V)
Val = (0.35 × 1023) ÷ 5 = 71.61 = 71 (Approximately)
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

16. DIGITAL CONTROLLER DS18B20
ADC Value Calculation
For,
29 Degree Celsius (0.29V)
Val = (0.29 × 1023) ÷ 5 = 59.33 = 59 (Approximately)
For ,
35 Degree Celsius (0.35V)
Val = (0.35 × 1023) ÷ 5 = 71.61 = 71 (Approximately)
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

17. Complete circuit with LM35 temperature
sensor

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

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

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

21. Complete circuit using DS18B20 temperature
sensor

22. Temperature increased but no voltage is
generating from DS18B20

23. LM35 ANALOGUE CIRCUIT

24. DS18B20 ANALOGUE CIRCUIT

25. LM35 DIGITAL CIRCUIT

26. 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);

27. DS1820 DIGITAL CIRCUIT

28. 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);
}

29. 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

30. REFERENCE
https://techshopbd.com/

31. 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.