Factory firmware for the M5Stack Unit CardKB2 (SKU: U215), built with ESP-IDF. It provides matrix keyboard scanning, RGB status LED, and key output over I2C / UART / ESP-NOW / BLE HID—including manufacturing / QA hooks such as I2C-triggered production-test mode.

Operating mode

Mode	Description
I2C (default)	I2C slave reports characters / key data to the host.
UART	Custom frames with key index and press / release over UART.
ESP-NOW	Broadcasts key frames (similar framing to UART).
BLE HID	Bluetooth HID keyboard, including arrow keys via Fn combos.

Switching modes

Hold Fn + Sym, then press 1 / 2 / 3 / 4 on the top number row to select I2C / UART / ESP-NOW / BLE HID respectively.

Note: Fn + 1 alone (top-left number key) sends ESC in most modes; it does not switch modes.

Build environment

idf version: ESP-IDF v6.1-dev-dirty

cd src
idf.py set-target esp32c61
idf.py build
idf.py -p <PORT> flash monitor

License

This project is licensed under the MIT License—see LICENSE.