Kauz
I always kinda wanted a guitar pickup that selectively picks vibrations of every string individually, having 6 separate independent outputs. Wanted not badly enough to justify buying one of commercial units, which exist and are not that expensive, or building my own.
After winding my own one-string guitar pickup for a one-string guitar (that was a separate project) I thought, maybe I will give it a go, it's not that hard after all. I've also seen one DIY attempt on the internet of building such a pickup using tape heads, which are basically also coils, just with fancy magnetic circuit around.
Later when reading about the component abuse challenge on Hackaday something clicked in my brain. In the description an ignition coil was mentioned and I thought "hey, every coil is a pickup coil if you're brave enough". Not just tape heads, but electric motors, magnetic valves, ignition coils, wireless charging modules, lots of stuff has coils inside, which could pick some of the magnetic field of a vibrating magnetized string.
Not gonna lie, I've also seen coils taken from relays used as pickup coils on a DIY-pickup on the internet. But I didn't want to go that way, I wanted to abuse the component, not kill it and use its internals for something else. I tested if the coil of an unmodified relay can give a usable signal and it did! I learned what I needed to amplify the signal in a couple of weeks and built a fully functional hexaphonic pickup. It's surprisingly good for what it is: the coil of a relay is designed to produce magnetic field almost exclusively within the magnetic circuit it's wound around, leaving just a small gap for the contact motion, but that gap is enough for the magnetic field of the string to get inside of this circuit.
Now there are several ways to use this setup. It can be used just as a gimmick, a totally normal pickup made of unnecessarily abused components. Or it can do something, regular pickups cannot do. First of all, I've made a board that mixes 6 signals from 6 strings to two channels. It can be used as a stereo effect such that different strings sound like they're coming from different "directions", or it can be used to apply different effects to different strings, as if one plays two different guitars connected to two different signal chains/amps/speakers.
The second thing I want to do in future is polyphonic MIDI-output. It is pretty tricky to recognize several notes being played simultaneously if all you have is a mix of those notes sounding together. Most DIY guitar MIDI trackers are monophonic. By having access to 6 separate signals and having computing power of 6 guitar tuners combined it should be possible to make a proper polyphonic instrument. Wait for the updates.
