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STeMCell devboard
The STeMCell is a STM32 based development board with Pro Micro pinout – designed by u/megamind4089.
Published January 18, 2022
The STeMCell, a STM32 based controller board is megamind4089's first design for ergo keyboards. It has a Pro Micro compatible footprint and is open source.
Github repo: https://github.com/megamind4089/STeMCell
Works with both QMK and ZMK.
I have added a quick and dirty UART DMA split implementation for ZMK, which works – megamind4089.
https://github.com/megamind4089/zmk/tree/mine
https://github.com/megamind4089/qmk_firmware
Features:
- Pro Micro footprint
- STM32F4x1 series MCU
- Support swapping TX/RX pins
- Jumper to enable/disable USB DFU bootloader
- Inbuilt TX pullup for UART half duplex communication
- User LED
- Extra 5 pinout on bottom
- Supports QMK and ZMK
- Tiny-uf2 bootloader
Oshpark link: https://oshpark.com/shared_projects/LJiMLzWF
The author's main motivation was the flash memory: "with Atmega32 there is not enough memory, to load all RGB animations and enabled via/ encoder/oled. Have to compromise on some features. STMf4 processor has lots of memory to load all features at once and another driving point is ZMK support."
I know RP2040 might be the future for both firmware. But we are looking at months for full support with both firmware. Thought this can be the interim solution – megamind4089.
As SouthPawEngineer points out, the STeMCell is similar to his Kestrel F0 which used the STM32F0 series of microcontrollers, aiming to be more functional but also more affordable.
The issue has been that the pandemic supply related issues have made the supply of pretty much all STM32Fx series of microcontrollers either very hard to come by or have rocketed up the cost of the controllers by 3-4x in some cases – SouthPawEngineer.
Published on Tue 18th Jan 2022. Featured in KBD #62 (source).
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