Op-Amp Circuit: Thermostat Fan
This is an op-amp circuit that turns on a fan when the temperature goes above a certain threshold. The threshold can be adjusted with a potentiometer.
The Circuit
R2 and the thermistor creates a voltage divider that will output a voltage based on the temperature. The opamp compares this voltage with the voltage from the potentiometer. If the voltage from the potentiometer is higher, the output is low. If the voltage from the thermistor is higher, then output becomes high.
When the output of the opamp is high, the transistor turns on, which turns on the fan.
Parts List
R1,RV1
10k
Thermistor
10k NTC
D2
1N4007
Q1
2N2222
R2
4.7k
M1
Fan
U1
LM741
How To Build
This project can be powered by a 9V battery. To test the circuit, you can connect it on a breadboard like shown below:
