// the setup function runs once when you press reset or power the board

void setup() {

  // initialize digital pin LED_BUILTIN as an output.

  pinMode(13, OUTPUT);

}

// the loop function runs over and over again forever

void loop() {

  digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)

  delay(1000);                       // wait for a second

  digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW

  delay(1000);                       // wait for a second

}