const int LED_PIN = 11;
byte brightness = 0;

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

void loop() {
  while (brightness < 255) {
    analogWrite(LED_PIN, brightness);
    delay(10);
    brightness += 1;
  }

  while (brightness > 0) {
    analogWrite(LED_PIN, brightness);
    delay(10);
    brightness -= 1;
  }

  delay(1000);
}