How to Control DC Motor with Arduino: Simple Guide

To control a DC motor with Arduino, use a motor driver like the L298N or a transistor circuit connected to Arduino pins. Write code to set the motor direction and speed using digitalWrite() for direction and analogWrite() for speed control via PWM signals.

Syntax

To control a DC motor, you typically use two Arduino pins: one for direction and one for speed (PWM). The main functions are:

• pinMode(pin, OUTPUT); - sets the pin as output.
• digitalWrite(pin, HIGH/LOW); - sets motor direction.
• analogWrite(pin, value); - controls motor speed with PWM (0-255).

You connect the motor driver inputs to these pins and power the motor separately.

arduino

pinMode(directionPin, OUTPUT);
pinMode(speedPin, OUTPUT);
digitalWrite(directionPin, HIGH); // Motor forward
analogWrite(speedPin, 200); // Speed control (0-255)

Example

This example shows how to control a DC motor's direction and speed using an Arduino and an L298N motor driver. The motor runs forward at half speed for 3 seconds, then backward at full speed for 3 seconds.

arduino

const int directionPin = 8;
const int speedPin = 9;

void setup() {
  pinMode(directionPin, OUTPUT);
  pinMode(speedPin, OUTPUT);
}

void loop() {
  // Motor forward at half speed
  digitalWrite(directionPin, HIGH);
  analogWrite(speedPin, 128); // 50% speed
  delay(3000);

  // Motor backward at full speed
  digitalWrite(directionPin, LOW);
  analogWrite(speedPin, 255); // 100% speed
  delay(3000);
}

Output

Motor runs forward at half speed for 3 seconds, then backward at full speed for 3 seconds, repeating.

Common Pitfalls

• Not using a motor driver or transistor can damage the Arduino because motors draw more current than Arduino pins can supply.
• Forgetting to connect the motor power supply ground to Arduino ground causes erratic behavior.
• Using digitalWrite() instead of analogWrite() for speed control means the motor runs only full on or off.
• Not adding a flyback diode when using transistors can damage components from voltage spikes.

arduino

/* Wrong way: Directly powering motor from Arduino pin (can damage Arduino) */
pinMode(9, OUTPUT);
digitalWrite(9, HIGH); // Not recommended

/* Right way: Use motor driver or transistor with PWM */
pinMode(9, OUTPUT);
analogWrite(9, 128); // Safe speed control

Quick Reference

Function	Purpose	Usage Example
pinMode(pin, OUTPUT)	Set pin as output	pinMode(8, OUTPUT);
digitalWrite(pin, HIGH/LOW)	Set motor direction	digitalWrite(8, HIGH);
analogWrite(pin, 0-255)	Control motor speed with PWM	analogWrite(9, 128);
delay(milliseconds)	Pause program	delay(3000);

Key Takeaways

Always use a motor driver or transistor to protect the Arduino from high current.

Use digitalWrite to set motor direction and analogWrite for speed control with PWM.

Connect the motor power supply ground to Arduino ground to avoid erratic motor behavior.

Add a flyback diode when using transistors to protect from voltage spikes.

Test motor control with simple code before adding complexity.