Building a PID controller to control the temperature of a (IIRC) piezoelectric cooler (or was it a hot plate? I don't remember exactly) was such a fun exercise.

Building a PID controller to control the temperature of a (IIRC) piezoelectric cooler (or was it a hot plate? I don't remember exactly) was such a fun exercise. It took me until like 3am to get it working, most fun I had in junior year physics lab.