Thermal Touch Switch using op-amp 741

Various types of switch circuits like a light operated switch, sound operated switch, etc is already posted on www.bestengineeringprojects.com. Now here is a thermal touch switch that automatic on and off due to the increase and decrease of pre-defined temperature. This type of circuit is useful to operate fans, cooler, etc.

Circuit description of thermal touch switch using operational amplifier 741

The circuit comprises an operational amplifier IC (IC₁), silicon diode (D₁ and D₂), and a few passive components to complete the circuit. Diode D₁ is used here as a temperature sensor. OP-amp 741 is used here as a comparator.

When the temperature is low, diode D₁ does not connect and the output of IC₁ is low when the temperature increases D₁ starts conducting and the output of IC₁ is high, which further glow LED LED₂.

For adjustment of pre-define temperature put switch SW₁ on and adjust potentiometer VR₁ so that output at pin 6 is half of the supply voltage.

NOTE: To control appliance according to temperature use relay with driver circuit at output pin 6.

Check out other touch-operated switches posted in bestengineeringprojects.com

1. Touch Switch Circuit using Transistor
2. Touch Switch-Cum-Heat Operated Switch
3. Clap Switch Cum Touch Switch
4. Thermal Touch Switch using op-amp 741
5. Simple Touch Switch Using Two Transistors

PARTS LIST OF THERMAL TOUCH SWITCH USING OPERATIONAL AMPLIFIER 741

Resistor (all ¼-watt, ± 5% Carbon)

R1, R2 = 10 KΩ R3 = 4.7 KΩ R4, R5 = 1 KΩ R6 = 1 MΩ R7 = 10 MΩ R8, R9 = 470Ω VR1 = 10 KΩ

Capacitors

C1 = 100 µF, 10V (Electrolytic Capacitor) C2 = 10 KpF (Ceramic Disc)

Semiconductors

IC1 = LM741 (Operational Amplifier) D1, D2 = 1N4148 (Small Signal Diode)

Miscellaneous

SW1 = On/off Switch LED1, LED2