This is a dump of all the files that I used to build my custom mech keyboard.
To prepare the base layout I used keyboard-layout-editor.
I ended-up with 15x5 layout with split space. This was my key requirement since what I really wanted was a keyboard with mouse functions built-in. Now, using arrows as mouse movements and split keyboard as left-mid-right mouse buttons I do not need mouse at all. Well, maybe this is not the most usefull and ergonomic way to handle mouse but hey, this is all for fun, right?
I tweaked the layout several times since than. The only constraint is the location of the 4 2u keys: space(s) and Enter.
I created a PCB and schematic sketch using excellent klepcbgen tool. This was a good starting point to tweak the design to match my ideas. I had some experience in designing PCBs and electonic circuits in general (see my ZX Spectrum Diy project so it was quite easy.
But all in all it was not that great - I totally failed with LEDs since I did not use proper footprint for WS2812B-2020 leds. So after I got the boards from JLCPBC it turned out that I cannot use LEDs at all. What you see now is a revised version that I did not (yet) put into production.
Other than that the board worked perfectly.
This is a fun project so I would not use any ready-to-use firmware. Anyway I don't think that any of available firmwares would allow me to use mouse. So I wrote my own simple version of keyboard handler using Arduino Micro templates and examples. The firmware uses HID-project.