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DC Motor Speed Control (Transistor + Arduino)

Drive a DC motor from one pin through a transistor and vary its speed with PWM. Learn transistor switching and flyback protection.

Beginner25 min

What you need

Wiring

Arduino Uno
NPN transistor
DC motor

Hover a pin or a wire to trace the connection.

Code

dc_motor.ino
// Ramp a DC motor's speed up and down with PWM through a transistor.
const int motorPin = 9; // PWM -> transistor base (through a resistor)

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

void loop() {
  for (int s = 0; s <= 255; s += 5) { analogWrite(motorPin, s); delay(50); } // speed up
  delay(1000);
  for (int s = 255; s >= 0; s -= 5) { analogWrite(motorPin, s); delay(50); } // slow down
  delay(1000);
}

Steps

  1. Transistor: base to D9 through a 1kΩ resistor, emitter to GND, collector to one motor terminal.
  2. Motor's other terminal to +5V (use an external supply; share ground with the Arduino).
  3. Add a 1N4001 flyback diode across the motor (band/stripe toward +5V).
  4. Upload — the motor ramps up and down. Never wire a motor straight to a pin.