[Dominik’s] daughter had an old toy piano that she loved, but when the batteries started to die down, it played awful tones and sounded generally out of tune. While this is likely something our circuit bending friends might be interested in, [Dominik] preferred when things sounded more cheery.
He considered simply replacing the batteries, but it seemed like a far better idea to do away with them altogether. he hunted around for a solution, and eventually found one at the local IKEA store. He grabbed a LJUSA hand-powered flashlight and disassembled it, saving the crank and circuitry.
He installed the crank on the back side of his daughter’s piano, and mounted the electronic bits inside the toy’s shell. The crank spins a brushless motor, generating an AC current which is rectified to DC before being stored in a capacitor. He says that a 30 second crank will play just a few tunes, which isn’t ideal, though it is better than frequently replacing batteries.