int ledPin = 9;  // PWM pin

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

  void loop() {
  for (int brightness = 0; brightness <= 255; brightness += 5) {
 analogWrite(ledPin, brightness);
 delay(100);
 }
  for (int brightness = 255; brightness >= 0; brightness -= 5) {
 analogWrite(ledPin, brightness);
 delay(100);
}
 }