//Initializing LED Pin
int led_pin = 13;

void setup() {
  //Declaring LED pin as output
  pinMode(led_pin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  for ( int i = 256; i > 0; i--)
  {
    analogWrite(led_pin, i);
    delay (10);
  }
  delay (2000);
  for ( int i = 0; i < 256; i++)
  {
    analogWrite(led_pin, i);
    delay (10);
  }
  delay (2000);
}