void setup() {
    // initialize digital pin 2 as an output.
    pinMode(2, OUTPUT);
  }
  
  // the loop function runs over and over again forever
  void loop() {
    digitalWrite(2, HIGH);  // turn the LED on (HIGH is the voltage level)
    delay(1000);                      // wait for a second
    digitalWrite(2, LOW);   // turn the LED off by making the voltage LOW
    delay(1000);                      // wait for a second
  }