Arduino LED Fade Using PWM (analogWrite)

The question

An LED is on PWM pin 10. Make it fade in from 0 to 255 and then fade out back to 0, changing the brightness by 1 each step with a 20 ms delay.

The sketch

void setup() {
  pinMode(10, OUTPUT);
}

void loop() {
  for (int b = 0; b <= 255; b += 1) {
    analogWrite(10, b);
    delay(20);
  }
  for (int b = 255; b >= 0; b -= 1) {
    analogWrite(10, b);
    delay(20);
  }
}

Wiring

LED → 220Ω → pin 10 (a ~ PWM pin); cathode → GND.

How it works

1. 1Only pins marked ~ (3, 5, 6, 9, 10, 11 on an Uno) support PWM.
2. 2analogWrite(pin, value) takes 0 (off) to 255 (full brightness).
3. 3One for loop counts up to fade in, a second counts down to fade out.