This is a PCB for a bluetooth split 12x5 ortholinear keyboard:
- Based on Adafruit's 32u4 Feather beard.
- Wireless (BLE) and wired (USB-C) mode.
- LED backlight.
- There are two 6x2 halves with identical PCBs. The master half runs the QMK firmware, and handles USB, BLE and battery charging. The slave half is responsible for only reporting its state to master over I2C.
- Extra TRRS jack on the slave half, making it possible to chain other I2C peripherals (think pedals).
- The board is flashed with the QMK firmware -- see my fork .
Bluetooth
The PCB uses the Raytac MDBT-40 module for bluetooth. QMK has built-in support for that module when flashed with Adafruit's SPIFriend firmware.
Since the Bluetooth module connects to the SPI bus, remember to flash the CPU before the Bluetooth module. Otherwise, the SPI bus will be taken and ICSP won't work.
LED backlight
This keyboard has LED backlight, however:
- The drivers I used (TLC59711) draw quite some current on stand-by that makes them unsuitable for battery-powered devices. I chose them because I already had some left over from a previous project.
- Since the keyboard is "borderless", some switches have been rotated so that components can fit between them. As a result, the backlight is uneven and would not be suitable for actual backlit keys.
- The two halves operate backlight independently as of now, so any advanced animation would have to utilise the I2C bus.
Known issues:
I designed this keyboard just for fun and as such it has some shortcomings:
- The BLE module is somewhat hard to come by -- Mouser has it but it was out of stock the few times I checked. Moreover, the Adafruit firmware for it is closed source and you can only download binary images.
- Power management could be a lot better. Moreover, the keyboeard does not really have a stand-by state, instead, there is a switch that simply cuts all power from the battery.
- The BLE module has enough processing power to handle everything the CPU does now, but can't quite run QMK as of now. (Another reason for sticking with 32u4 is that it can easily be programmed over USB)