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
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
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
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.