int ledPin = D2;
void setup() {
  // We want to tell the Argon that we'll use
  // D2 as an output pin.
  pinMode(ledPin, OUTPUT);
}

void loop() {
    // led on for 3 sec
    digitalWrite(ledPin, HIGH);
    delay(3000);
    // led sleep for 3 sec
    digitalWrite(ledPin, LOW);
    delay(3000);
}