Niklas Roy created this whimsical synthesizer from a hollowed out birch log. Using an ATMega8 as the tone generator, the design of the device is quite simple but charming in its execution.
The contacts for the different tones are wired to felt balls covered in conductive yarn. The user places the balls inside the birch log and plays the notes by touching them with a hammer. The hammer is connected to ground, thus completing the circuit and making the synthesizer chime its chippy notes.
Full documentation for this project can be found at Niklas’ site should you choose to try it out for yourself.