zmk/app/boards/shields/mf68

MF68

Replacement MagicForce 68 PCB designed by di0ib.
Hardware repo: https://github.com/di0ib/tmk_keyboard/tree/master/keyboard/mf68

This shield is made to be easily used with an Adafruit Feather nRF52840 Express, and the default pin order is optimized for that board. For use with a Pro Micro-compatible controller, comment lines 21-41 and uncomment lines 44-64 in mf68.overlay.

Features

• Designed for Pro Micro boards
• PWM backlight control (with optional FDS6630A, not configured)
• Mini USB port for DIY case

Default layout

Use with an Adafruit Feather nRF52840 Express

Pinout

Pro Micro Left	Feather Left	Feather Right	Pro Micro Right
D3	A2		RAW
D2	A3	GND*	GND
GND		RST*	RESET
GND			VCC
D1	A4	D5	F4
D0	A5	D6	F5
D4	SCK	D9	F6
C6	MO	D10	F7
D7	MI	D11	B1
E6	RX	D12	B3
B4	TX	D13	B2
B5		A0	B6

But why not a Pro Micro-compatible microcontroller?

Availability and sometimes cost. Sometimes it's hard to find them or the developers straight up stop producing them, sad but common in the mechanical keyboards community. On the other hand, the Feather nRF52840 Express is more widely available and I doubt it's gonna be discontinued anytime soon.

I was unable to use the D2 pin, and using the SDA pin caused issues.
In the board definitions, UART is disabled since the RX and TX pins are used for the matrix, same for SPI and SCK/MO/MI pins.
SCL and SDA pins are available for I2C but disabled by default, uncomment lines 84-91 in app/boards/arm/adafruit_feather_nrf52840/adafruit_feather_nrf52840.dts to enable.
The QSPI flash is disabled too, if needed uncomment lines 103-125 in the same file.

The space inside the MagicForce68 case is very, very limited, and physical modifications to the case, like the removal of inner support, are necessary; I also had to desolder the JST connector and remove the black holder from the SWD connector from the Feather, basically making it flat. For the same reason, forget about putting a battery inside: best case scenario it just doesn't fit, worst case scenario it gets punctured by the solder joints (which is as bad as it sounds). I'm gonna try with a 18650 battery on the outside.

If adding backlight to your board with this controller, remember that Adafruit says that it's not safe to pull 500mA from the regulator when connected to 5V (read: USB).