My college physics department had a lab full of Commodore 64s. They had a cool accessory that let you hook up a ribbon cable to the bus lines on the motherboard so that you could build peripherals on a breadboard and have them interact with programs running on the computer.

My final project for the digital electronics class (1993) was a Commodore 64 that could control the frequency of the sound from a speaker and listen with a microphone for the sound resonating in whatever room it was in. The program was written in Assembly, which is kind of a pain. We hooked it up to a big cardboard tube full of helium to measure the speed of sound. I think there was also a way to get out the ratio of the constant pressure and constant volume heat capacities of helium, too.

Thanks for the trip in the wayback machine.