void setup() {

  // put your setup code here, to run once:

  pinMode(LED_BUILTIN, OUTPUT);

}

void loop() {

  // put your main code here, to run repeatedly:

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

  delay(1000);             // wait for a second

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

  delay(1000);             // wait for a second

}