void setup() {
   pinMode(13, OUTPUT); //set pin 13 as output
}
void loop() {
    digitalWrite(13, HIGH); //set  pin 13 high (+5v)
  delay(1000); //wait 1000 ms = 1 second
  digitalWrite(13, LOW); //set pin 13 low (0v)
  delay(1000); //wait 1 second
  }