Good for you! Did you use an Arduino? I've used both an Arduino and an evaluation board for the PIC18 (I built two controllers).
I programmed the test-strip feature to put the base exposure at the left, center, or right-end of the test-strip. I usually use "center". "Left" is good for determining how much to burn, and "right" is good for deciding a dodge.
One feature I really like is turning off the safelight when the enlarger is on for any reason (focusing or exposing). I used a relay, but a triac should work equally well.
To conserve space on the LCD, I use tenths of stops for everything, which works well for exposure arithmetic, but it can't represent third or quarter stops. For those, I must use steps of 0.2 or 0.3 stops instead.
I used an STM32F4 for mine, but it could just as easily have been a PIC18/24 or any of the AVR/Arduino devices. The STM32 was simply what I had in stock.
Mine also switches off the safelight (and I can set the safelight brightness on it, dimming the 12V LED safelight bulb I use). For simplicity I also use a relay to switch the enlarger bulb on and off.
I've never thought of placing the base exposure elswhere than on the right-hand side of the paper (I'm right handed so that's most convenient to start for me). Your method of left-middle-right sound very useful though, you might have motivated me there to update my software a little...
The reason I built this timer is to make most of a darkroom session. There's only a few hours available in an evening and it takes some time to set things up in my makeshift darkroom, so I want to be as productive as possible.
For me, that's (f-)stop printing using an automated timer.
But without one, it's easy to just follow the aperture numbers on any vintage lens and use those as your exposure times for a test strip (2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, ...). As someone said before, that will give you a half-stop incremental test strip, which is what I use most as a first (and quite often the only needed) test strip. A cheat sheet of the incremental exposure times would be useful ofcourse. Hence the reason for me to build my timer...
Unless my memory is gone (very probable) the "F" in f stop is an abbreviated, or shortened version of "mathematical Factor", it is generally shortened to "f/5.6" or a slightly longer "factor/5.6"
Pretty much everything to do with film photography, including printing, is governed by mathematical factors that we undertake to obtain correct exposure. Whether that be done by looking up charts, using a specially designed darkroom timer or other methods, such as working out the mathematical factor ourselves to obtain the correct exposure to light sensitive materials. All of these methods use a factor derived from a mathematical calculation to give us the desired result.
Using f/stop timing one could reduce the exposure by 1 whole stop by changing the lens by half a stop and and by changing the exposure by half a stop to get the desired result.
I always assumed that F was short for Focal length; e.g. aperture diameter in mm = focal length / aperture number?
But still, I think naming it factor makes sense in a way here (and could very well be valid as well, as my knowledge is purely gathered on a hobbyist-basis
)