#define PWM_PIN 9  // Define the PWM output pin

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

void loop() {
  // Increase brightness
  for (int duty = 0; duty <= 255; duty++) {
    analogWrite(PWM_PIN, duty);
    delay(10);
  }

  // Decrease brightness
  for (int duty = 255; duty >= 0; duty--) {
    analogWrite(PWM_PIN, duty);
    delay(10);
  }
}