Temperature Controlled Fan with Utsource

Today we are going to learn how to build a cooling fan which automatically turns on when the temperature is high above certain level. For this we are going to use C945 NPN transistor as the main controller and a thermistor as the temperature sensing device. Thermistors are also a type of resistors which changes their resistance with the temperature. All the resistors change their resistance with the temperature but thermistors change their resistance significantly with any temperature variation.

Key Components :

We will need few other components to complete this project. All the components are given with their corresponding order links from https://www.utsource.net/ So, you can order the components easily.

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Circuit Diagram:

This is the basic circuit diagram of the temperature controlled fan circuit. C945 Transistor’s collector is connected to the negative lead of the cooling fan. Base of the C945 transistor is connected to the voltage divider created by the thermistor and the 220Ω resistor.

Step By Step Guide:

Step 1: Arrange the components

Step 2: Solder 220Ω resistor across the emitter and base pins of the C945 transistor.

Step 3: Solder the thermistor as shown in the circuit diagram.

Step 4: Solder the Fan wires to the collector of the C945 transistor and positive supply as shown in the circuit diagram.

Step 5: Connect the power supply as shown in the circuit. Now the circuit is ready you can test it.

How It Works:

When temperature is high the resistance of the thermistor will decrease. This will cause the increase of voltage across 220Ω resistor. This will cause the C945 transistor to trigger and fan to turn ON.

Conclusion:

You can use this circuit as a exhaust fan controller. Also you can control a AC fan with this circuit by using a 9V relay in the place of the 9V fan in the circuit diagram.