I've lately been working on a functioning keyswitch keychain. I finally got around to making a thread on gh about it with some details
The original concept was to make a tiny keyswitch keychain that fits entirely within the profile of a keycap but still acts as a fully functioning keyswitch. I'm still working on the firmware, but I've got it to the point where it can emulate a standard keyboard; it also has some entertaining alternate modes such as morse code input.
I searched for quite a while for a controller that would fit in the space constraints, since everyone's favorite atmega328 is just too large, making routing difficult. The trick was to find the smallest USB controller without going to some unfriendly, wafer-level package. I ended up using an SiLabs 8051 chip with a 3x3mm QFN package. Honestly, it's quite nice; hopefully more people use it in the future for tiny builds.
There are some 0.1" headers exposed -- the plan is to allow daisy-chaining of multiple keychains via i2c/smbus so that wiring up a macropad/numpad is super simple. If anyone knows of any similar projects, please let me know so I can make the protocols compatible. Otherwise I'll try to come up with something simple and reusable.
Anyways, last time I posted about this, a ton of people expressed interest in buying one, so I'm hoping to run a small groupbuy through the friendly folks at
crowdsupply. I still have a ton of work to do though -- planning on releasing the firmware+schematics as open-source once I finish up this next revision. I'm also hoping to integrate an rgb led on the pcb, as well as make it (somehow) matias compatible.
Let me know if you guys have any questions, happy to share notes! Also, does anyone know where to get Matias keycaps in singles?