I thought you all might be interested in a project I have underway.
First of all, I am an occasional 5x7 shooter, though I do not love the process of doing tray development. I had been using a Taylor 10-key timer, like this:
Which was cool, until a hair-thin wire broke, and I didn't feel like doing the micro-surgery necessary to repair it; I went back to my ancient GE wind-up X-ray timer and counting "one-one-thousand" to myself. That inspired me to make my own timer, which I call the Darktimer, as an open-source project. (Open source in this case meaning you can download the source code, and I'll be producing a wiring diagram and enough information to build one yourself for about $40 in parts.)
The Darktimer is, as its name suggests, aimed specifically at darkroom processing. It has no lights on it, so is suitable for use with open trays. It has one Big Red Button (and some smaller buttons for setting up timers), and can be easily programmed with a series of timers which will run sequentially, requiring just pressing the BRB each time. So I, for instance, would program it with a 60 second timer (prewash), an 8:30 timer (development), a 30 second timer (stop), a 2 minute timer (fixer, obviously variable depending on the state of the fixer), a 10 minute timer for final water wash, and then 30 seconds for rinsing agent. Press the BRB once to start the prewash timer. Press again to start the development timer, and so on. No complex interaction required in the dark.
Each timer beeps once per second, so you know it's going. Each timer has a setting you can change (per timer), which will do a double-beep every N seconds (think agitation reminder), and a longer beep every minute. The final five seconds have higher-pitched triple beeps before the final "you're done" sound, to give you some time to get film and stop bath together at exactly the right instant.
The whole thing is built out of an Arduino board, a little LCD screen, four pushbuttons, one power switch, a speaker, and a battery pack. Construction is pretty simple -- maybe not first-project simple, but pretty simple -- and building the circuit would take maybe a couple hours at most. Honestly, the Arduino is vastly overpowered for this project, but it's cheap and easy to use.
I've got my prototype to the point that it does (almost) everything it should, and I've got materials in hand to turn it into a finished-enough product. If there's any interest here, I'll post a link to the project page once I have it up, which will contain all the information you need to build one yourself. I'm open to questions, and if you have feedback, I'm interested in hearing it, though it probably won't get rolled into this first version, since I'm almost done.
Sounds interesting and useful! I'd check out the link if you publish something and be tempted to construct it.
For a version 2, it'd be nice if I could select named sequences, like I could program a set of times for FP4+ and another set of times for TMY2. I'd need a adjustable triple beep interval as my combiplan takes a whole lot more than 5 seconds to drain.
Not interested. Please look at the apps and dedicated hardware that already exist. Some apps include a display in various safe-light colors, too. Oh, and cheap digital kitchen timers.
Thanks for your feedback Jac, but I'm trying to avoid having any light at all, so phone apps aren't helpful. I've never seen a programmable system quite like this, and really, the point was to build a fun project to my specifications. If it works for someone else, awesome, but that's a by-product.
jp, the final beeps could easily be configurable in the UI, that's a good idea for v2. Even as it stands, it's very easy to configure the number of final beeps, but you have to do it on the computer, before loading the firmware. I also like the idea of named sequences, that would be very handy for different workflows.
I would think that a once-per-second beep for minutes on end would get tiresome. You may reconsider your choice after using it for a while.
My Zone VI developing timer beeps once every 30 seconds as an agitation reminder.
The Zone VI is a count-up timer so requires no programming. I can reset it between steps in about a second using the footswitch. The cost of this simplicity is that it needs a display (it uses dim red LEDs), which is contrary to your design objective.
You might find a footswitch handy as an alternative to your BRB.
Steve: agreed, the beep-per-second may well get old, although it's better than the silent-until-it-explodes nature of kitchen timers. It may be that turning off the one-second beep and just leaving the interval beep is the right choice. I'll figure that out after I use it a couple times. I like the footswitch idea, although in my particular setup, I also like the idea of the timer being small and easily packed away -- in my new house, the most appropriate/light-tight bathroom is pretty tight on space. Finding somewhere I could put a footswitch that wouldn't also be a tripping hazard would be difficult.
Of course, the joy of this kind of project is that if you don't like my design, it's pretty easy to wire up your own just the way you like it. It would also be really straightforward to have both the BRB and an optional footswitch that plugs in, which I'll keep in mind for the future.
I'd be very interested in this - in fact I had already thought about it and have most fo the parts assembled. My eldest is pretty good with arduino so I had planned on getting him to write the sketch. Have you considered adding a temp compensation to it? My idea was similar to the other compensating timers out there (now unobtainium it seems). In arduino terms - take a temp measurement once at the start, apply adjustment to set time to compensate for temp and then count down. So if you were under temp, and with a set time of 2 min, then at first press it would adjust to 2.20 say, and count down. A series of beeps in the last 10sec might be worth considering. A foot switch is another good idea - they are cheap on ebay and can just be wired in parallel to the main button.
A beep every second controlled with a volume control is a great aid to dodging and burning. Decades ago I designed and built an analog timer (alas, no beep!) that could be switched between the three modes of focus, time, and stop with a simple foot switch. A foot switch isn't necessary, but is convenient. The safelight switched on when the enlarger was off and vice versa. A logarithmic tapered volume control expanded the short exposures and compressed the long exposures. Three decade switches would have had the advantage of being accurately set in the dark.
Woodturner-fran: I hadn't thought about a temperature compensation, that's an interesting idea. I had the impression that temperature compensation wasn't a linear function, but a quick check with the XTOL datasheet (since that's what I'm most used to) suggests it's at least pretty close to linear. Regardless, I'll have the code up soon; I'm slowly working on the project page, which I'll post here once it's ready. With the code and a few extra parts, you're set. Hopefully, I've written the code to be clear enough that it should be hackable, too, so it shouldn't be too much work to add a temperature compensation feature (though adding the UI for it will be noticeably more work).
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