Show HN: I turned my iPhone and a $20 smart plug into an f-stop timer (peterszentkiralyi.eu)
52 points by pentakkusu 8 hours ago
I am a film photographer and do some darkroom printing and always wanted one of the proper, advanced f-stop timers, but never really wanted to spend a couple hundred dollars on one. Eventually I figured my phone was already perfectly capable of doing the timing, it just needed a way to switch the enlarger.
So I built Darkplug around a cheap smart plug. The app controls the enlarger over the local network and does regular timing, f-stop timing, test strips, has an intuitive dodge/burn workflow, split grade (2 timing channels) and paper development timing.
I’ve been using it for a few months in my improvised bathroom darkroom.
Fair warning: the app was blindly vibe coded using Codex and Xcode.
pimlottc an hour ago
I get that red-on-black color scheme is a nod to the red lighting of a dark room, but the contrast is so low I can hardly read the example screenshots.
guax 29 minutes ago
It’s not a nod. It’s required to not ruin the paper during use. A specific yellow would also work but phone screens often output more than just the desired color. Red is the safest.
pimlottc 16 minutes ago
That's fine, just make the versions on the website readable for people who aren't in a darkroom.
baoooooooooooo 30 minutes ago
Isn't it more than a nod, and actually a hard requirement to be considered for use in an active darkroom?
It hadn't occurred to me that now with OLEDs you can actually safely limit exposure to wavelengths that would be damaging to the development process - I'd imagine that is what the author is shooting for here
arnarbi 5 hours ago
Very cool. Is it controlling the plugs via direct Bluetooth connection? Or zigbee via a hub, or wifi (direct or via service)?
I always assumed, probably incorrectly, that there would be too much jitter in the actual timing so I had built a few prototypes of e.g. an esp8266 controlled relay, where you would give the MCU a duration rather than separate on/off commands. But I guess that was wildly over-optimizing. In your case, how stable is the delay from the app sending a command until the switch operates?
I'd add voice mode for color printing in total darkness.
jrflo 3 hours ago
I was curious about timing accuracy too, has any testing been done on this? Is it accurate to 1s, 0.1s, 0.01s? How dependent is it on the smart switch hardware?
alnwlsn 27 minutes ago
I'd probably put the typical smart switch hardware/software stack at around 0.25 seconds. Maybe you can but I don't think I'd try to rely on anything much faster than that.
If you did, I would go in the custom firmware for the smart switch direction. A lot of them are just an ESP32 inside, and you could probably get to 0.001 seconds that way (but you are switching AC which cycles on the order of 0.02 seconds, so whatever)
muhehe 2 hours ago
I played with development photos in a darkroom a long time ago. I don't think one second actually makes much difference.
guax 28 minutes ago
mmmlinux an hour ago
25$ to unlock all the features...
sailingcode 2 hours ago
Good idea. I wonder if the iPhone's camera would be able to measure the projected negative and guide exposure time?
Sarkie an hour ago
I had no idea what an enlarger was.