Analog photography is a fascinating area of art, combining creativity with interesting chemical processes. Staple of doing analog work the way it is meant to be done is printing of your work. Enlarger is a device that projects light through a negative onto a surface on which photosensitive paper is to be placed. Nowdays, old enlargers can be picked up for quite cheap, but they almost universally lack one thing- the timer. Yes you can flick on a switch, use stopwatch and turn it off, but timers can provide more control over the whole process. And since they are quite expensive, making your own is logical way forward.
I currently work on a prototype of Arduino controlled relay for that exact purpose. It is very simple circuit and code.
This project offers cheap alternative to usually expensove vintage (or new) darkroom timers. Uses just a handful of components
Now has functions of single button time changing in seconds, displayed on 6 LED in binary (didn't have 2 7-seg displays, but looks cooler none the less). One button executes, and one is for reset. Red LED in picture acts as relay until it ships.