Why this matters
Long-exposure astrophotography is limited by the Earth’s rotation: leave the shutter open too long and stars turn into streaks. Commercial star trackers that counter this motion are bulky and often cost upwards of $400, which is a high barrier for hobbyists. This project was about building a compact, low-cost “barn door” style star tracker that makes deep-sky photography more accessible.
How it works
A barn door tracker uses two hinged plates that rotate at the same angular speed as the Earth but in the opposite direction. By polar-aligning the hinge with the Earth’s axis and driving the top plate at roughly 15° per hour, the camera effectively stays locked on a patch of sky while the sensor gathers light. The device is sized to sit between a standard tripod and camera, keeping the setup portable for field use.
Design & build
I designed a three-plate chassis from 1/8" aluminum, with a curved #10-24 threaded rod controlling the opening of the “door.” The motion is driven by a belt system powered by an Arduino Uno, a ULN2003 driver and a 28BYJ-48 stepper motor, all powered from a USB power bank. Using simple motion mathematics, I derived the required rotation rate, translated it to motor RPM and finally to a 575 µs step delay so the tracker matches the Earth’s rotation. The finished prototype costs around $40 and is fully functional, with planned refinements including a proper belt drive, reduced play in the curved-rod guides and an integrated Arduino-based intervalometer.