int ledPin = 3;  // PWM pin
int brightness = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Fade in
  for (int brightness = 0; brightness <= 255; brightness++) {
    analogWrite(ledPin, brightness);
  //  delay(1);
  }
  Serial.println("fade in");
  // Fade out
  for (int brightness = 255; brightness >= 0; brightness--) {
    analogWrite(ledPin, brightness);
  //  delay(1);
  }
  Serial.println("faded out");
}