I buy a lot of electronic and mechanical junk at garage sales and antique stores with the intention of taking it apart to figure out how it works. In this video, I dismantle a desktop calculator and learn about the inner workings of its printer mechanism.
I bought an old Keurig coffee maker at a garage sale, but it never worked correctly, so I decided to put it to better use. I took it to pieces and built a craptacular sous-vide machine out of the parts. Then I used it to cook a steak in my workshop, and finished the steak off with a blowtorch. The end result was surprisingly delicious!
A little while back, I picked up an Arduino Starter Kit. It contains an Arduino Uno, a bunch of common components, and an instruction book that walks beginners through building circuits and using the Arduino to interact with hardware.
One of the projects in the book is a basic synthesizer that lets you play tones on a piezo speaker. The schematic for this is dead simple:
After getting the Arduino to play a few notes, I decided to extend the project a bit and play a melody. After a bit of screwing around, I managed to get the thing to play the Simpsons theme.
The code for this sketch can be found on GitHub.