USB_EN Desktop Controller (b43_huben)

5-key + 1-knob desktop controller PCB · USB wired · QMK firmware · VIA

b43_huben (USB_EN) is a small desktop controller PCB: STM32F103CBT6 (Blue Pill), 3-column × 3-row matrix, only 5 physical media keys plus one EC11 knob — a tiny desktop box for volume and playback. The knob uses two virtual key positions, so both directions can be remapped independently in VIA. QMK firmware, open source, VIA-compatible.

1. Specifications

Item	Value
PCB model	b43_huben (USB_EN)
Keys	5 physical keys + 1 knob
Matrix	3 columns × 3 rows (COL2ROW)
Connection	USB wired (single mode)
Port	USB Type-C (C-to-C supported)
MCU	STM32F103CBT6 (Blue Pill)
Knob	1 × EC11 encoder (C13 / C14, resolution 4)
USB VID / PID	0x7F89 / 0x4B43
Lighting	WS2812 @ B13 (8 LED positions in firmware)
Layers	4 (0–3, layer 7 reserved)
N-key rollover	Yes (NKRO)
Polling rate	1000 Hz
Firmware	QMK (open source)
Keymap tool	VIA (web)
Source code	github.com/micahyy/czm_qmk

2. Hardware / pinout (PCB design)

Function	Pin / value
Matrix	3 rows × 3 columns (COL2ROW)
Knob A / B	C13 / C14
Knob resolution	4 (ENCODER_RESOLUTION)
WS2812 data pin	B13
Bootloader	stm32duino

2.1 Knob virtual key positions

The firmware LAYOUT has 7 positions; row 2's ENL / ENR have no physical switch and belong to the knob:

Knob	CW	CCW
Knob 1	ENR	ENL

By default these are volume + / volume -. In VIA they are ordinary key positions and can be set per layer — e.g. scrolling, zooming or lighting control.

3. Lighting

• WS2812 on B13, 8 LED positions defined in firmware.
• Toggle, effect, speed and hue are available on layers 1 / 2 shortcuts and in the VIA Lighting tab.

4. Layers and shortcuts

All 5 keys are tap / hold (LT): tap = media function, hold = layer.

4.1 Layer 0 (default)

Position	Tap	Hold
Key 1	Open media player (MSEL)	Layer 1
Key 2	Play / Pause (MPLY)	Layer 2
Key 3	Mute	—
Key 4	Previous track (MPRV)	Layer 3
Key 5	Next track (MNXT)	Layer 4
Knob	Volume + / Volume -	—

4.2 Layer 1 (hold the media-player key — lighting)

Position	Key
Key 2 (play/pause)	RGB toggle (RM_TOGG)
Key 4 (previous)	Effect speed - (RM_SPDD)
Key 5 (next)	Effect speed + (RM_SPDU)
Knob CCW / CW	Hue - (RM_HUED) / Hue + (RM_HUEU)

4.3 Layer 2 (hold the play/pause key)

Position	Key
Key 1 (media player)	Next effect (RM_NEXT)

Layer 7 reserves factory reset (EE_CLR); the default layers have no direct entry, so map a key to layer 7 in VIA, or simply reflash the firmware to restore defaults.

5. VIA

1. Connect over USB and open VIA: CN server ｜ GitHub Pages
2. Load the keyboard definition JSON in the Design tab on first use
3. Switch to Configure and remap — changes apply instantly and are stored on the keyboard
4. All 7 positions are editable; ENL / ENR are the knob's CCW / CW

See also: Using VIA

6. Flashing

The PCB uses the stm32duino bootloader:

1. Enter bootloader: unplug USB, hold the top-left key and plug back in (QMK Bootmagic Lite) — the board enters DFU.
2. Flash:
   • QMK Toolbox with the compiled .bin; or
   • CLI: dfu-util -a 2 -d 1EAF:0003 -D <firmware>.bin
3. Re-plug when done.

The stock keymap has no QK_BOOT key: use the "hold the first key while plugging in" method, or map QK_BOOT in VIA.

7. Building the firmware

make czmao/b43_huben:via

Prebuilt binaries: GitHub Actions artifact firmware-b43_huben.

8. FAQ

Q: VIA does not detect the board? A: Use a WebHID-capable browser (Chrome / Edge) and load the definition JSON. Also try another port or cable.

Q: The knob turns the wrong way? A: Swap the ENL and ENR functions in VIA.

Q: Media keys do nothing in some apps? A: They use the standard USB Consumer Control page; some apps need "global media keys" enabled in their own settings.

Q: How do I restore the default keymap? A: Reflash the official firmware, or set the layout back in VIA.

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QQ group: 677654482

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📥 Firmware & source

• Firmware source (QMK): github.com/micahyy/czm_qmk (PCB path keyboards/czmao/b43_huben)
• Prebuilt firmware: GitHub Actions artifact firmware-b43_huben

See section 6 "Flashing" for flashing instructions.