Automatic Temperature Controlled Fan

As we have already published Clap-Operated remote control for fan previously. Now, here is the circuit of Automatic temperature controlled fan used to control the speed of fan according to change in temperature.

Circuit description

The circuit of automatic temperature controlled fan is build around temperature transducer AD590 followed by operational amplifier LM324. AD590 is a temperature transducer, change temperature into corresponding voltage. The output of transducer is given to pin 2 of IC2 LM324. The two reference voltage is given to pin 6 and pin 10 through variable resistor VR1 and VR2 respectively. The value of these variable resistor is fixed according to operating temperature (i.e. RL1 energized when temperature is above 300C and RL2 energized when temperature is below 230C). The output is taken from pin 7 and pin 8 which further given to base of transistor T1 and T2 through resistor R5 and R6 respectively. Transistor T1 and T2 is used as relay driver transistor. The two input is given from two different stage of regulator.

circuit diagram of automatic temperature controlled fan

Power supply Circuit:- The primary AC voltage is step down to 12 – 0 – 12 by using transformer X1 which further rectified using bridge rectifier (D1 through D4). The rectified output is filtered using capacitor and given to input pin 1 of voltage regulator IC 7812 (IC1). The regulated output is taken from pin 3 of IC1 where pin 2 is grounded.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 100 KΩ

R2 = 56 KΩ

R3 = 39 KΩ

R4, R5, R6 = 1 KΩ

VR1, VR2 = 10 KΩ (Preset)


C1 = 1000 µF/40V

C2, C3 = 1000 µF/25V

C4 = 0.1 µF


IC1 = LM7812 (12V regulator IC)

IC2 = LM324 (operational amplifier)

T1, T2 = SL100

D1 – D6 = 1N4001 (rectifier diode)


TT1 = AD590 (temperature transducer)

RL1, RL2 = 12V 200Ω

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