Show HN: I turned my iPhone and a $20 smart plug into an f-stop timer

pentakkusu

13 hours ago

73points

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.

23 comments

Comments

arnarbi•10 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.

Crosseye_Jack•4 hours ago

> How it works

> Set up your smart plug and note its local IP address. Make sure the plug and your iPhone or iPad share the same local network. Connect your enlarger to the smart plug. Enter the plug’s local IP address in Darkplug, and connect. Once set up, you can control the enlarger directly from your iPhone or iPad.

jrflo•9 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?

foobar1962•2 hours ago

Repeatability is more important than accuracy.

Note also that some of the best printers used metronomes to count exposure time and turn the enlarger light on and off manually.

muhehe•7 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•6 hours ago

Depends on how powerful of a light you’re using. 1 second on a 7 second exposure is too much. One second on a 20, not.

aw4rzs•4 hours ago

I don't think 1 second on a 7 second B+W exposure is that noticeable.

alnwlsn•6 hours 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)

quickthrowman•3 hours ago

If I were to tackle this project, I’d use an ESP32 and a relay with 120V contacts. That way you can use a GFCI receptacle and be code compliant if your darkroom is in a basement or the enlarger receptacle is near your darkroom sink.

pimlottc•7 hours 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•6 hours 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•6 hours ago

That's fine, just make the versions on the website readable for people who aren't in a darkroom.

plussed_reader•3 hours ago

What's the use case to use a darkroom tool outside the dark room?

baoooooooooooo•6 hours 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

macintux•1 hour ago

I upgraded to an Apple Watch Ultra because it offered a face with only red and black. It’s been long enough now that I don’t remember all the details, but I appreciated being able to monitor time in the darkroom (using DND to avoid flashes of light).

nottorp•1 hour ago

I'd like to endorse the plug choice :)

Shellys can be configured to connect to your wifi and are not dependent on any cloud service.

s0rce•4 hours ago

25 years ago my dad built me a darkroom timer with a relay and a PIC 16F84A. It only had one button that you used a combination of short and long presses to adjust the time (read on a 7 segment LED display) and trigger the exposure.

sailingcode•8 hours ago

Good idea. I wonder if the iPhone's camera would be able to measure the projected negative and guide exposure time?

mmmlinux•7 hours ago

25$ to unlock all the features...

dofm•5 hours ago

Nice. I have been meaning to do this with an e-ink device but other distractions keep getting in the way.

Sarkie•6 hours ago

I had no idea what an enlarger was.

maciekkmrk•5 hours ago

I recently took a B&W film development and printing class and it was very cool. I wouldn't be inclined to do it again, but it was fun to understand what 'dodging' and 'burning' refers too and get your hands do something.

aaronbrethorst•3 hours ago

The icons for the dodge and burn tools in Photoshop are directly cribbed from the tools you'd use in a darkroom, too ;) https://helpx.adobe.com/photoshop/desktop/repair-retouch/adj...