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AVR Legacy BLE Firmware

This page covers the common operations and limits of ATmega32U4 keyboards paired with nRF51822 wireless modules running legacy Adafruit Bluefruit LE firmware (referred to below as "legacy BLE firmware"). It applies to the legacy BLE firmware backend of G60, Kamilia, Command65, Manta 40s (Hotswap/Solderable/Ortho), and Skog Reboot.

:::info Third-party names

Adafruit and Bluefruit are used here only to identify legacy third-party firmware, compatible protocols, and companion tools accurately. These keyboards and nRF51822 wireless modules are not original Adafruit products. This project is not affiliated with, authorized, sponsored, or endorsed by Adafruit Industries. Bluefruit is a trademark of Adafruit Industries.

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How it works​

  • The AVR (ATmega32U4) handles matrix scanning and keyboard state.
  • The nRF51822 module handles BLE transport; the AVR drives it over UART with AT text commands.
  • The module runs a legacy Adafruit Bluefruit LE application with S110 SoftDevice 8.0.0.

Daily use and pairing​

Legacy Bluefruit does not provide DuoChord's five independent host slots. Do not use DuoChord BLE1–BLE5 / PAIR instructions with this backend.

  1. Connect a USB data cable and test typing.
  2. Hold Left Shift and Right Shift and press B to toggle USB / Bluetooth. Search for the keyboard in host Bluetooth settings and connect.
  3. If stale pairing blocks connection, hold both Shift keys and press Z twice within 1 second. Remove the old Bluetooth record on the host, then pair again. All keyboard-side bonds are cleared.

Mapped USB, BT, TOG and RST keys may also be available; positions depend on the keymap. For five host slots, follow the DuoChord migration guide.

Limits and notes​

  • The legacy BLE firmware uses the Bluefruit AT text protocol; very fast continuous typing may drop UART characters. Prefer wired mode for heavy high-speed input.
  • Each key must send both a press and a release HID report, otherwise the host may see a stuck key.
  • The legacy BLE firmware does not support the DuoChord binary protocol or five-slot management; the two firmwares are not interchangeable.
  • Migrating from legacy BLE firmware to DuoChord requires a fixed sequence, see Legacy BLE firmware → DuoChord first migration.

Troubleshooting​