// setup runs just one time
void setup() {
  pinMode(13, OUTPUT);  // define pin 13 (LED) as output
}

// loop runs forever
void loop() {
  digitalWrite(13, HIGH);   // set pin13 to High state
  delay(1000);              // Wait 1 sec
  digitalWrite(13, LOW);    // set pin13 to Low state
  delay(1000);              // Wait 1 sec
}