AutocadHow-ToBeginner · 3 min read

Which Pins Support PWM on Arduino Uno: Complete Guide

On the Arduino Uno, PWM (Pulse Width Modulation) is supported on digital pins 3, 5, 6, 9, 10, and 11. These pins can output analog-like signals using the analogWrite() function.

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Syntax

To generate a PWM signal on Arduino Uno, use the analogWrite(pin, value) function.

pin: The PWM-capable pin number (3, 5, 6, 9, 10, or 11).
value: The duty cycle from 0 (always off) to 255 (always on).

This function sets the pin to output a square wave with varying duty cycle, simulating analog voltage.

arduino

analogWrite(pin, value);

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Example

This example fades an LED connected to pin 9 using PWM. The LED brightness changes smoothly from off to fully on and back.

arduino

const int ledPin = 9;

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

void loop() {
  for (int brightness = 0; brightness <= 255; brightness++) {
    analogWrite(ledPin, brightness);
    delay(10);
  }
  for (int brightness = 255; brightness >= 0; brightness--) {
    analogWrite(ledPin, brightness);
    delay(10);
  }
}

Output

LED connected to pin 9 smoothly fades in and out repeatedly.

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Common Pitfalls

Many beginners try to use analogWrite() on pins that do not support PWM, which will not produce the expected analog output.

Also, remember that analogWrite() does not generate a true analog voltage but a PWM signal that can be smoothed with external components.

Using pins 0 and 1 for PWM is not recommended because they are used for serial communication.

arduino

/* Wrong: Using analogWrite on pin 2 (no PWM) */
analogWrite(2, 128); // This will not produce PWM

/* Right: Use a PWM pin like 3 */
analogWrite(3, 128); // Correct PWM output

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Quick Reference

PWM Pin	Description
3	PWM output pin
5	PWM output pin
6	PWM output pin
9	PWM output pin
10	PWM output pin
11	PWM output pin

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Key Takeaways

PWM on Arduino Uno is available only on pins 3, 5, 6, 9, 10, and 11.

Use analogWrite(pin, value) to set PWM duty cycle from 0 to 255.

Do not use analogWrite on pins without PWM support; it won't work.

PWM simulates analog output by switching the pin on and off rapidly.

Avoid using pins 0 and 1 for PWM as they are reserved for serial communication.