Following on from my successful 'Build a shutter tester for focal plane shutters, cheap, easy & it works'
Here is my design of a timer for B&W film developing.
Many, like myself, use a stopwatch or a three line LCD timer, however, I thought it would be good to move into the 21st century with a colour screen & better functionality.
The developing timer allows the user to easily program the, initial & secondary agitations and interval, as well as stop & fix times, by turning a dial.
The screen then steps though each process, showing green when running, yellow to give a 10 second warning of an action to take place (agitation for example) and then highlighted as the user has to carry out the action. Finished tasks then become grey. An audible cue will also be added.
Additionally, for twiddlers like myself, the timer drives a stepper motor to carry out all of the development agitation tasks & also stop & fix agitation if required. I will leave the debate as to whether to twiddle or not, to others. Myself, I find it much easier to leave the developing tank in the water bath and twiddle. It maintains a better temperature, does not aerate the developer, stops water dripping & alleviates the threat of spillage during agitations.
The hardware is all cheaply available on Aliexpress & uses many of the same parts as the shutter tester. Where possible, I have kept the wiring identical. Basic practical skills are required to build the timer. All of the required electronic modules are pre-built, so there is little or no soldering required, as push-fit or screw terminals are used for the connections.
Optionally, a li-po battery can be added, which is automatically charged & will power the timer in the event of a power failure.
Forum can be found here https://www.photrio.com/forum/threads/build-a-b-w-film-developing-timer-twiddler-cheap-easy-it-works.204682/#post-2766843