int led = 9;           // the pin that the LED is attached to
int brightness = 0;    // how bright the LED is
int fadeAmount = 5;    // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup() {
  // declare pin 9 to be an output:
    pinMode(led, OUTPUT);
    }

    // the loop routine runs over and over again forever:
    void loop() {
      // set the brightness of pin 9:
        analogWrite(led, brightness);

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

              // reverse the direction of the fading at the ends of the fade:
                if (brightness == 0 || brightness == 255) {
                    fadeAmount = -fadeAmount ;
                      }
                        // wait for 30 milliseconds to see the dimming effect
                          delay(20);
                          }