If you’ve done anything with electronics in the past forty years or so you’ve likely come across the 555 timer IC. It’s small, simple and incredibly useful. I used one as the timing source for a “T-Bird tailights” project in a digital electronics course I took as an elective. The actual chip is fairly small and easy to understand, especially with the interactive die explorer near the bottom.
Don’t forget to check the notes at the end, especially the large-size 555 timer created by Evil Mad Scientist Lab.