int ledPin = 9;    // LED connected to digital pin 9
int brightness = 0; // How bright the LED is
int fadeAmount = 5; // How many points to fade the LED by

void setup() {
  pinMode(ledPin, OUTPUT); // Set the LED pin as an output
}

void loop() {
  analogWrite(ledPin, brightness); // Set the brightness of the LED

  brightness = brightness + fadeAmount; // Change the brightness for next time through the loop

  // Reverse the direction of the fading at the ends of the fade:
  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount; // Change the direction of the fade
  }

  delay(50); // Wait for 30 milliseconds to see the dimming effect
}