How to Control a DC Fan Using Arduino PWM (with Circuit Diagram)

Keywords: Arduino fan control, PWM, transistor, temperature fan control

How to Control a DC Fan Using Arduino PWM (with Circuit Diagram)

Controlling the speed of a DC fan is one of the most practical applications for beginners working with Arduino. Pulse Width Modulation (PWM) allows us to adjust the speed of a fan smoothly and efficiently without expensive hardware.

In this tutorial, you'll learn how to:

• Use an Arduino to control a 2-wire DC fan

• Apply PWM to change speed

• Build the full circuit with a transistor and diode

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What You'll Need

Component	Quantity
Arduino Uno	1
2-wire DC fan (5V–9V)	1
NPN transistor (e.g. 2N2222 or BC547)	1
1kΩ resistor (base resistor)	1
Diode (1N4007 or 1N5819)	1
Breadboard and jumper wires	—
External power supply (9V battery or adapter)	1 (optional for 9V fans)

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Circuit Diagram

Explanation:

• The transistor acts as a switch. It receives a PWM signal from Arduino on its base through a 1kΩ resistor.

• The diode is connected across the fan terminals in reverse bias to protect from voltage spikes (flyback diode).

• The fan is powered from the 9V source (or Arduino 5V for smaller fans).

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📄 Arduino Code

c++

int fanPin = 9; // Connects to the transistor base

void setup() {
  pinMode(fanPin, OUTPUT);
}

void loop() {
  // Increase fan speed gradually
  for (int speed = 0; speed <= 255; speed += 5) {
    analogWrite(fanPin, speed);
    delay(100);
  }
  delay(2000);

  // Decrease fan speed gradually
  for (int speed = 255; speed >= 0; speed -= 5) {
    analogWrite(fanPin, speed);
    delay(100);
  }
  delay(2000);
}

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Tips:

• Use analogWrite() to generate PWM on pins 3, 5, 6, 9, 10, or 11.

• Don't power a 9V fan directly from Arduino — use an external source with a shared GND.

• Don't power a 9V fan directly from Arduino — use an external source with a shared GND.

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Conclusion

Using PWM with Arduino to control a fan is simple and educational. This same principle can be applied to control LEDs, motors, heaters, and more. For automatic control, you can even combine this with a temperature sensor like LM35 — which we’ll cover in a future tutorial.