Touch screen darkroom timer

[radu_c]

I made this timer a few years back but never got around to post it in the DIY section. It's running on a plain Arduino Mega board (dirt cheap nowadays) and a 2.8" TFT screen I had lying around from a tool I made in the past. I wrote the code in C++ but then modified it to be flashed straight from the Arduino programming tool.
I made the code open-source and it's available here. There you also find instructions how to flash it on a board if anyone wants to make one. The repository also contains the files for 3D printing the case. The enlarger is controlled via a relay right now but a solid state switch can also be used as long as the signal input is 3.3V to 5V.




When I'm not using it in the darkroom, I use the same device as a thermostat for home brewing my kombucha . I just flash the thermostat code and now it's a thermostat. Kombucha tastes awesome BTW if anyone in the Boston area is interested in a LF chit-chat and a glass of home-brewed bootch.

On to the features:

Main screen has the regular options: manual on/off to focus the enlarger and the main timer for doing the exposure.



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[radu_c]

The main timer can be set with the "adjust" button. Also as an added feature, the display luminosity can be controlled with the "dimmer" function. It's true the TFT is not a true safe-light ... light, but it's hardly a strong light and I never had any issues with fogging the paper or anything. In any rate, it can be dimmed to very low. Don't pay attention to the number itself, it represents the duty cycle of the PWM signal in 8-bits (techno-babel).



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[radu_c]

As a final touch, the timer can also time the Development, Stopping and Fixing times. All 4 timers are stored, adjusted and ran independently (though not concurrently as the Arduino is a single thread processor).



These three timers don't control the relay but activate a buzzer when the time is up (makes a short beep). The main enlarger timer also makes a beeeeeeep when the time is up, although it's redundant because you see the light getting turned off at the end of the exposure.

The case is 3D printed (files included in the repository) with bio-degradable PLA.

This is the timer I've been using for quite some time and I quite like it. It's gone through a few revisions but the core is essentially unchanged.
I know, I know, you can buy one off the auction site for <insert-low-number-here> dollars but this is more about the thrill of the build.

Hope you enjoy.

[jp]

Looks good!