int led = 9;
int brightness = 0;
int faceAmount = 5;

void setup() {
  pinMode(led, OUTPUT);
  // put your setup code here, to run once:

}

void loop() {
  analogWrite(led, brightness);

  brightness = brightness + faceAmount;
  
  if (brightness <= 0 || brightness >= 255) {
    faceAmount  = -faceAmount;
  }

  delay(30);

  // put your main code here, to run repeatedly:

}