int i = 0;
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin 13 as an output.
  pinMode(13, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  for(i = 0; i < 255; i++)
  {
    digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(3); // wait for a second
  }
  for(i = 255; i > 0; i--)
  {
    digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW
    delay(3);   // wait for a second
  }
                
  
}