const int PIN_LED = D2;   //pin D2

void setup() {
  //initialize the pin mode
  pinMode(PIN_LED, OUTPUT);
}

void loop() { 
  digitalWrite(PIN_LED, HIGH); //turn LED on
  delay(100);				   //delay 100 ms
  digitalWrite(PIN_LED, LOW);  //turn LED off
  delay(100);		         //delay 100 ms
}