int ledPin = D2;


void setup() {
    // Tell the Argon that we'll use D2 as an output pin.
    pinMode(ledPin, OUTPUT);
}


void loop() {
    // Turn on
    digitalWrite(ledPin, HIGH);   // Turn ON the LED pins
    delay(3000);               // Wait for 3 seconds
    
    // Turn off
    digitalWrite(ledPin, LOW);   // Turn OFF the LED pins
    delay(3000);               // Wait for 3 seconds
    // Repeat
}