#define LED_PIN 3

int power = 5;
bool increase = true;

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

void loop() {
  while (true) {
    increase = (power == 0 || power == 250) ? !increase : increase;
    analogWrite(LED_PIN, power);
    power += (increase) ? 5 : -5;
    Serial.println(power);
    delay(100);
  }
}