Darkplug’s Print screen, from the maker’s announcement.
Film printers who wanted an f-stop timer faced a few-hundred-dollar box. Peter Szentkiralyi’s answer is an app that switches the enlarger lamp through a cheap smart plug.
In a darkroom print, an enlarger projects the negative onto light-sensitive paper, and the timer decides how long the lamp stays on. An f-stop timer counts that time in photographic stops, so “one stop more” means double the exposure however long the base time is. Dedicated ones are a boutique product. Szentkiralyi, a film photographer printing in a makeshift bathroom darkroom, wrote on Hacker News that they never wanted to spend a couple hundred dollars on one, and noticed a phone could do the timing if something else switched the light.
That something is a Shelly smart plug. You plug the enlarger into it, type its local IP address into the app, and the phone controls the lamp over your home network. The listing says no account or cloud service is needed for core timer operation.
The interface is red on black, and the reason is practical: black-and-white paper is worked under a dim red or amber safelight, and a bright white screen would fog it. A commenter found the screenshots too low-contrast to read; the maker’s answer was that eyes adapt in the dark.
The app is free to download with a plain timer. A single in-app purchase, Darkplug+ at $24.99 in the US, unlocks f-stop timing, guided test strips, dodge-and-burn planning (with exportable plan codes), split-grade printing and a guided developing timer. The maker describes it as under $50 for app plus plug.
Limits, stated plainly. It works only with Shelly plugs: the listing names six models from Plus Plug S Gen2 to Plug US Gen4, and the maker confirmed no other brand is supported. It needs iOS 18.6 or later; it runs on iPad too. Timing runs through a network switch, so precision depends on the plug. The maker measured about 0.1 second using slow-motion video; one HN commenter guessed typical smart switches lag around a quarter-second. That is fine for exposures of several seconds, less so for very short ones. The maker also says the app was vibe-coded with Codex and Xcode. It reached the App Store on September 20, 2026.