PulseHeartbeat.c

/**
 * PulseHeartbeat
 * 
 * Blink the onboard LED to signal "Yepp, we are still runnning".
 * The onbaord LED is on pin 13 and so pin 13 will be set to OUTPUT.
 * 
 * Call this at the beginning of your loop() function.
 * Caution: Will only work if millis() if functional and no one else
 *          did hook up timer0.
 */
void PulseHeartbeat(void) {
  static unsigned long lastMillis = 0;

  if(0 == lastMillis) {
    pinMode(13, OUTPUT);
  }
  
  lastMillis = millis();
  digitalWrite(13, ((lastMillis / 1000) % 2 ? HIGH : LOW));
}