Tad’s Awesome Darkroom Timer

This is Tad’s Awesome Darkroom Timer — a simple, reliable, and safe timer for anyone who develops film or prints in the darkroom.

Commercial timers I tried (Paterson, Gralab, Smiths, even cheap digital stopwatches) all had issues: unreadable under safelight, scary buzzers, mechanical failure, or brittle plastic. So I built my own.

Here's my video showing how it works:

Features:

Two modes: Stopwatch (for paper developing) and Countdown (for film developing)

Minute tones: Keeps you on track without staring at the display

Simple interface: Three anodized aluminum buttons — green = start, red = stop, black = reset

Darkroom safe: Big red LED display with a filter gel bezel

Memory: Remembers your preferred mode across power cycles

Optional ticking: Turn ticking on/off with a button combo

USB-C powered: Works with any standard USB charger

I designed and 3D printed the case, with threaded inserts for M3 screws and a stepped bezel to hold the gel filter. Inside you’ll find an Arduino Nano, a TM1637 LED display, a piezo buzzer, and a USB-C trigger board for clean power.

I can’t sell these — they take close to an hour each to assemble neatly, and I’d have to charge over $200 to make it worth the effort. Instead, I’m sharing everything for free: code, case files, and parts list.

👉 GitHub repository (code + models): https://github.com/harrist4/darkroom-timer