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Fade an LED with PWM (Arduino)

Smoothly fade an LED brighter and dimmer using analogWrite on a PWM pin. Learn pulse-width modulation and for-loops.

Beginner15 min

What you need

Wiring

Arduino Uno
LED

Hover a pin or a wire to trace the connection.

Code

fade.ino
// Fade an LED up and down using PWM (analogWrite).
// Use a PWM-capable pin — on the Uno these are marked with ~ (3,5,6,9,10,11).

const int ledPin = 9;

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

void loop() {
  for (int b = 0; b <= 255; b++) { analogWrite(ledPin, b); delay(8); } // fade up
  for (int b = 255; b >= 0; b--) { analogWrite(ledPin, b); delay(8); } // fade down
}

Steps

  1. Wire the LED from D9 through a 220Ω resistor; cathode to GND.
  2. D9 must be a PWM pin (marked ~ on the board).
  3. Upload the sketch. The LED breathes smoothly up and down.
  4. Try changing the delay to speed up or slow down the fade.