Star trails are the paths left by stars as seen from the earth. As the earth spins, the stars appear to move and circle in the sky.

To capture the star trails you need a camera, a tripod and an automated trigger for your camera. The Arduino, a relay and the camera’s remote control will create the automated trigger.

Project Steps

Fritzing schematic.

The system is powered by 12 volts. The transistor turns the relay on when pin 2 is set to HIGH.

This fires the IR remote control that triggers the DSLR.

The Arduino code can’t be more simple. Just decide the time between photos and put that time after the command that sets pin 2 LOW.

Remember that your DLSR must have time to take and process the photos. If you set your camera to a 10-second exposure you must have 25 to 200 seconds delay between exposures.

Peel back the adhesive paper on top of the DLSR remote control and solder two wires to the two pads under the button.

Place the adhesive paper back in place.

Connect the two wires to the contacts of your relay.

Finally, go to or There you can download the software which will merge your individual photos together and create star trail photos like this one.