That looks great! So the keyboard itself has a digital interface rather than needing scanning?
Yes, it comes with its own 2040 that does does the USB HID and a I2C node that provides config, keystroke (down/held/up), touchpad delta-since-last-poll, backlight control and several raw access registers, including managing an interupt pin (which I'm not using right now).
Pretty neat for using with a mini-Linux machine or in a embedded setup.
The i2C interface can provide ascii with direct modification (shift/alt) or provide just the keycodes. Might also be a good candidate for an espruino module.
I also implemented a nice dimming effect, which unfortunately makes the little power bank shut down due to low power consumption :) Mapped the dim-down onto a key combo now and use it as an off switch until I might replace the battery with something simpler.
Works great for now with that singe-file Espruino solution.
The vertical opportunity would have been doing everthing with just the keyboard module and a 1.8V nRF. But that would have meant a new board, casing, flow soldering instead of just soldering four cables. But it might run well on a 3V coin cell instead of the "bone".
and is that one of those special buttons at the top where you can rub your thumb over it and scroll around?
Yes. Great addition to the keyboard.