Modified version of VT-40 PCB with IO expander and XIAO BLE microcontroller.
For a long time a wanted to build a wireless keyboard, and because I had few of the VT-40 PCBs laying around, I decided to modify it to work with a BLE capable microcroller. For the microcontroller I chode XIAO BLE, which is new cheap uC with nrf52840. The only problem was that it only has 11 GPIOs and you need at least 16 GPIOs for Planck layout. I decided to use IO expander MCP23017 which has 16 GPIOs and can communicate with uC via I2C.
I decided to make a small PCB for MCP23017 which would fit into space where RPi Pico is supposed to be. I also made a PCB for uC with pinheader for connecting IO Expaner and other periferals.
For the build I used KTT Seasalt Lemons lubed with Krytox 205g0. They are mounted on 2.5mm plate printed from black PLA and there's also foam between pcb and plate for better sound.
Case was designed in Autodesk Inventor and is made out of 5 parts - 3 for the main frame, bottom with slight angle and top to cover all the electronics. The PCB is mounted with a little slides inside the main frame, so no screws are needed.
I decided to make bottom part i bit more interesting, so I generated random pattern of rectangles in Blender, and then imported it to Inventor.
At first I wanted to try ZMK firmware, but because I could get the matrix working I decided to use KMK firmware. I also wrote a custom scanner for MCP23017.