It started with a cheap, punch-card programmable manual music box. Thirty-one hobby servos later, it ended as an automated MIDI music box, with a short pit stop as a keyboard-driven MIDI device.
If you think you’ve seen the music box in [mitexela]’s video below before, you’re right. [Martin], musician, inventor, and father of the marvelous marble music machine, took an interest in these music boxes and their programming a while back. Like [Martin], [mitexela] started his music box project with punch card programming, but he quickly grew tired of the bothersome process, even after automating production with a laser cutter. He decided to do away with the punch cards completely and devised a method to pluck all 30 notes using a few large handfuls of hobby servos. One servo, converted to continuous rotation, spins the drum, with the rest linked to small laser-cut acrylic plectrums via stiff brass wire. The fingers imitate the punched holes passing over the drum and pluck the notes according to MIDI messages. The whole thing can draw quite a bit of current, so in addition to a beefy power supply, [mitexelea] optimized the code to minimize power requirements. This had the happy consequence of reducing the latency enough to allow the music box to be played from a MIDI keyboard in real time.
A lot of work went into this one, but [mitexela] isn’t resting on his laurels; he has a full slate of improvements that he wants to tackle, not least of which is SD card support for MIDI files to turn this into a jukebox. We’re looking forward to the updates.
Thanks to [HolyCrapCakes] for the tip.