int ledPin = D2;
int ledPin2 = D3;

void setup() {
// We want to tell the Argon that we'll use
  // D2 as an output pin.
  pinMode(ledPin, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop() {
    
    digitalWrite(ledPin, HIGH);
    digitalWrite(ledPin2, LOW);
    delay(500); 
    digitalWrite(ledPin, LOW);
    digitalWrite(ledPin2, HIGH);
    delay(500); 
}