void setup() {
  // initialize digital pin LED_BUILTIN as an output
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  // turn the LED on (HIGH is the voltage level)
  digitalWrite(LED_BUILTIN, HIGH);
  // wait for a 100 ms
  delay(100);
  // turn the LED off by making the voltage LOW                    
  digitalWrite(LED_BUILTIN, LOW);
  // wait for a 100 ms
  delay(100);
}