Camera intervalometer Arduino code

Timelapse.ino

#define FOCUS   11
#define SHUTTER 13

/*
 * Pins 11 and 13 go to two reed relays, which connect the ring pin of a
 * headphone jack to the other two pins. These are connected to the camera via
 * a 2.5mm phone patch cord.  Set your camera ISO and aperture to expose well
 * in the darkest conditions you anticipate occurring during the timelapse. The
 * camera should be set to auto-expose on aperture-priority mode, so that the
 * focus and depth of field remain constant from frame to frame. Delay is
 * configured to take a little less than 3,000 frames in a 24 hour period
 * (filling up a 16GiB SD card).
 */

void pulse(int pin, unsigned long ms) {
  digitalWrite(pin, HIGH);
  delay(ms);
  digitalWrite(pin, LOW);
}

void setup() {
  pinMode(FOCUS, OUTPUT);
  pinMode(SHUTTER, OUTPUT);
  
  digitalWrite(FOCUS, LOW);
  digitalWrite(SHUTTER, LOW);
}

void loop() {
  pulse(FOCUS, 2500);
  for(;;) {
    pulse(SHUTTER, 500);
    delay(31046);
  }
}