#define DUTY_CYCLE 192  // Duty cycle for the PWM over [0,255]
 
void setup() {
   pinMode(13, OUTPUT);  
}


void loop() {
   analogWrite(13, DUTY_CYCLE);  
   delay(1000);                       // time delay in msec before repeat

  
   for (int fadeValue = 0 ; fadeValue <= 255; fadeValue += 5) {
      analogWrite(13, fadeValue);
      delay(30); 
   }

   
   for (int fadeValue = 255 ; fadeValue >= 0; fadeValue -= 5) {
      analogWrite(13, fadeValue);
      delay(30);
   }
}