This project has a long history.
Over a decade ago, I was looking for something I could plug into my camera (a Digital Rebel XTi at the time) that would perform a sequence of light frames to stack. It was something I'd use when doing wide-angle photography, untethered from a computer or autoguider. There were few options then, and they tended to be expensive. I ended up throwing something together with an Atmel ATmega48 microcontroller and a 7-segment display on a piece of Radio Shack perfboard in a dremeled-out project box, and it worked. And I used it for years. Until last year, when I lost it. Left it behind at a dark sky site. Probably freaked someone out...
Anyhow, I bought a cheap intervalometer online and used it for awhile, but was annoyed by it every time I used it. Setting the time and exposure count is kind of tedious. It's not readable in the dark without pressing a button to light it up, and it's easy to press the wrong button and stop your sequence. When I'm out in the dark, I usually have one camera doing a stack while I take starry landscape photos with another, and I want to be able to tell at a glance how much time or how many shots remain in the stack.
Earlier this year, as part of another project, I learned how to design custom circuit boards, and I realized I could bring my astrophotography timer back, better than before. I also have a 3D printer and a bit of experience with OpenSCAD, so I could design a custom enclosure for it.
Anyhow, the project (C source code, KiCad schematic and PCB, OpenSCAD enclosure) is all online here: https://github.com/j...ey0/astro-timer
The rotary encoder control knob is new in this iteration of the project, and it makes adjusting the exposure length super quick. Another thing this can do that other tools don't is send a mirror-lockup pulse ahead of each frame.
There are a lot more options in this space than there were a decade ago, some of them involving smartphones or whatnot, but I like a simple, easily-readable device that'll run for hundreds of hours on a pair of alkaline batteries (at a low brightness setting). So I built this thing. Does this project interest anyone else? What kind of thing do you wish you could do with something that plugs into your camera's remote shutter release port?