Fading an LED with PWM

Use a loop and analogWrite together to produce a smooth, continuous breathing fade instead of fixed brightness steps.

You'll need: the same LED-on-a-PWM-pin wiring from Lesson ard-08.

Lesson ard-08 ended by suggesting a loop that ramps brightness up and down — this lesson builds that properly, introducing the for loop, one of the most useful pieces of syntax for repeating an action with a changing value each time.

void setup() {
  pinMode(9, OUTPUT);
}

void loop() {
  for (int level = 0; level <= 255; level++) {
    analogWrite(9, level);
    delay(8);
  }
  for (int level = 255; level >= 0; level--) {
    analogWrite(9, level);
    delay(8);
  }
}

A for loop has three parts, separated by semicolons: a starting value (int level = 0), a condition checked before each repeat (level <= 255), and an action performed after each repeat (level++, which increases level by one). Together, this counts level from 0 to 255, calling analogWrite(9, level) at every step along the way — exactly 256 brightness steps, each held for 8 milliseconds, producing a fade that takes just about two seconds up, then two seconds back down.

Try changing the delay(8) value: a smaller number fades faster, a larger number fades slower — a simple, safe way to get comfortable adjusting a for loop's behavior before writing one from scratch yourself.