Elmot's Vintage Keyboard

This project is a Zephyr-based firmware for converting vintage typewriters (like the Brother AX110) into modern USB and Bluetooth Low Energy (BLE) HID devices. It uses the Zephyr RTOS to handle USB device stacks, BLE advertising, and input matrix scanning.

Hardware

Designed to run on boards like the nrf52840dk, nrf52840dongle, and nrf5340dk.

The following table describes the pinout for each supported board.

Pinout

Function	nRF52840-DK	nRF52840-DONGLE	nRF5340-DK (cpuapp)	Color
I2C SCL	P0.31	P0.31	P1.03
I2C SDA	P0.30	P0.29	P1.02
CAPS LOCK LED	P0.13	P0.13	P1.14	Red
PWR LED	P1.11	P0.22	P1.10	Green
BLE LED	P1.10	P0.15	P1.12	Blue
USB LED	P1.12	P0.17	P1.11	Red

Pins reserved for future use:

Function	nRF52840-DK	nRF52840-DONGLE	nRF5340-DK (cpuapp)	Color
LED 1(not used yet)	P0.14
LED 2(not used yet)	P0.15
On-module button			P1.06
SX1509B interrupt			P0.02
LD1			P0.06	Green
LD2R			P0.08	Red
LD2G			P1.09	Green
LD2B			P0.12	Blue

GPIO extender: Semtech SX1509B (connected via I2C)

Key Features

• Dual Connectivity: Supports both USB HID and BLE HID.
• Dynamic Key Mapping: Translates raw scan codes into standard HID key codes.
• Modifier Support: Handles standard modifiers (Shift, Ctrl, Alt) and special function keys.
• Blue Alt Mode: A custom function layer activated by a specific key.

Blue Alt Layer

When the blue ALT key is pressed and held, several keys change their functionality to provide common modern keyboard features that are missing from the vintage layout.

Original Key (Nordic layout)	Function	Blue ALT Function
L IND	TAB	ESC
CODE	Left CTRL	Left CTRL
1,2 ... 0	1,2 ... 0	F1 - F10
Top row ? ,`	/, `	F11, F12
RELOC	PG UP	HOME
INDEX/REV	PG DOWN	END
W	W	UP
A	A	LEFT
S	S	DOWN
D	D	RIGHT
V	V	~
WORD OUT/LINE OUT	ALT	ALT

Keys Functionality

The key mapping is defined in src/ax110keys.c. It maps raw 16-bit scan codes to HID key codes.

Build and Flash

The project is built using the Zephyr build system (west).

west build -b <board_name>
west flash

nRF52840dongle

nRF5340 only

Flashing Network Core

On the nRF5340-DK, you must also flash the network core with the Bluetooth controller firmware.

1. Build the network core image (usually located in a build_net directory):
   1. Linux/MacOS

      west build -b nrf5340dk/nrf5340/cpunet -d build_net $ZEPHYR_BASE/samples/bluetooth/hci_ipc

   2. Windows PowerShell

      west build -b nrf5340dk/nrf5340/cpunet -d build_net $env:ZEPHYR_BASE/samples/bluetooth/hci_ipc

2. Flash the network core:

   west flash -d build_net