#7.4.3. LED

void setup() {

  analogWrite(9, 0);

}

void loop() {

  for (int bright = 0; bright <= 255; bright++) {

    analogWrite(9, bright);

    delay(4);

  }

  for (int bright = 255; bright >= 0; bright--) {

    analogWrite(9, bright);

    delay(4);

  }

}