Last completed (so not something which is still going on) project i have learned a lot was for "digital- and microcontroller technology" classes.
I designed a tower which fits on a pc fan. In this tower there is a tabletennis ball and on top of it is a infrared sensor. With a Potentiometer you can set the height at which the ball shall float.
As microcontroller i took an arduino uno. For visualization i used SerialComInstruments.
Learned lots of microcontroller programming, pid controls and how the fuck a serial port communication really works.

Green is PWM signal, red is ball height, black horizontal line is target height

So awesome. I want to get into stuff like this someday. Kudos, dude.

Thanks a lot :) it is not that hard! Especially if you dont want to get into hardcore-c-only-every-nanosecond-costs-life microcontroller programming but come into hardware programming i would reeeally recommend you arduino hardware (ok, tbh i recommend you the chinese clones bc original is just way too expensive) and this arduino-related programming language which is like C but with a lot of library stuff.. You wont get a professional mC programer (i'm neither :D), but you get a profound insight into hw programming.

Btw, thats a photo of an oscilloscope. First signal is "set an arduimo output high and low as fast as arduino language can do", next 3 signals are "making the same, but 3 times and in pure C (bitmanipulation, i hope thats the right word in english *blush*):