void setup() {  // program section that runs once
   pinMode(D0, OUTPUT);//assign pin 13 as an output
}

// the loop function runs over and over again forever

void loop() {  //runs program over and over until stopped
   digitalWrite(D0, HIGH); // turn the LED on
   delay(1000); // wait for one second
   digitalWrite(D0, LOW); // turn the LED off
   delay(1000); 
}