I was inspired by Youtuber Device Orchestra to try turning a sonic toothbrush into a synthesizer. I got it to work and have made a couple videos: https://www.youtube.com/channel/UCtBIAIUupbJChgrajTvapSQ

In case anyone cares I'm sending MIDI to an Arduino board which I programmed to handle the events using a MIDI library. I then convert the midi notes to a frequency which I pulse on two digital pins driving an H bridge, which I hook up directly to the coil on the brush.