#define LED 3


void setup() {
  pinMode(LED, OUTPUT);
}

void loop() {
  int x =0;
  for(int i=0; i<4; i++) {

    analogWrite(LED, x);
    delay(500);

    x = x + 255 * 1/3;
    }
    
  int y = 255;
  for(int i=0; i<4; i++){

    analogWrite(LED, y);
    delay(500);

    y = y - 255 * 1/3;
  }

}