So, the idea of the arduino intervalometer is to trigger a camera at a set interval – therefore the first thing to figure out, is how to actually triggering the camera.
Most DSLRs have a pretty straight-forward way of triggering the camera, using the remote port. Opening the port, you find three pins, one ground, one for auto-focus and one for taking the picture.
Connect ground to #2, the camera focuses, and connect ground to #3, it takes a picture.
Disable auto
When shooting with an intervalomer, you will want to disable autofocus, and set the camera for manual focus. You can see below why using autofocus when shooting a timelapse is a bad idea
Apart from disabling autofocus, you should also disable other automatic controls such as whitebalance and lightmetering.
So all we need to do, is connect gnd and #3 pin – though you might want to experiment, some cameras won’t take the picture without #2 being connected to gnd, even if autofocus is disabled!
What I did, was I used the connector from a remote I had lying around.