#define LED_PIN 13
 
void setup () {
    pinMode (LED_PIN, OUTPUT);     // enable pin 13 for digital output
}
 
void loop () {
    digitalWrite (LED_PIN, HIGH);  // turn on the LED
    delay (1000);                  // wait one second (1000 milliseconds)
    digitalWrite (LED_PIN, LOW);   // turn off the LED
    delay (1000);                  // wait one second
}