htx-studio · lalithaar · Aug 28, 2025
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+# **One-Handed Keyboard**
+
+> We received a very special email. The sender’s daughter was tragically hit by a heavy truck on her way to school and permanently lost the use of her right hand. When using a computer, she has to constantly switch between the keyboard and the mouse, making typing slow and exhausting. He asked us to help create a one-handed keyboard for her.
+
+![Left-hand small keyboard](/Docs/Image/左手小键盘右侧面.jpg "Left-hand small keyboard")
+
+![Left-hand large keyboard](/Docs/Image/左手大键盘右侧.jpg "Left-hand large keyboard")
+
+This is a single-mode mechanical keyboard with a built-in trackball. The firmware uses [QMK](https://github.com/qmk/qmk_firmware). Many thanks to all developers who contribute to the QMK community.
+
+Keyboard inspiration: [Video by He Tongxue (Bilibili)](https://www.bilibili.com/video/BV1DtjAzUEb9)
+
+Hardware open-source files: [HTXStudio One-Handed Keyboard](https://oshwhub.com/htx-studio/One-Handed_Keyboard)
+
+[GitHub repository](https://github.com/htx-studio/One-Handed-Keyboard)
+[Gitee repository](https://gitee.com/htxstudio/one-handed-keyboard)
+
+Development setup guide is [here](https://docs.qmk.fm/newbs_getting_started "Set up your QMK environment"). The firmware source code is [here](https://github.com/htx-studio/qmk_firmware/tree/master/keyboards/htx_studio).
+
+This repository contains:
+
+* Eight PCB designs for three different keyboard models (both left- and right-handed), with LCSC EDA project files.
+* VIA remapping configuration files and precompiled firmware.
+* 3D model design files.
+
+---
+
+## Repository Structure
+
+#### Docs (Documentation)
+
+Datasheets and images of the chips.
+
+#### Firmware
+
+QMK firmware for the three keyboard models, plus VIA keymap JSON files.
+
+#### Hardware
+
+LCSC EDA project files.
+
+#### Model
+
+3D model files and machining files for each keyboard model.
+
+---
+
+## Build Guide
+
+### PCB:
+
+1. Right-hand keyboard – Hot-swappable (large): FR-4, 1.6mm thick, 4 layers, JLC04161H-3313 stackup, impedance control ±20%.
+2. Left-hand keyboard – Soldered (small): FR-4, 1.6mm thick, 2 layers. ALPS yellow switches require firm pressing during installation.
+3. Left-hand keyboard – Hot-swappable (large): FR-4, 1.6mm thick, 4 layers, JLC04161H-3313 stackup, impedance control ±20%.
+4. Type-C daughterboard: FR-4, 1.6mm thick, 2 layers, marked CON1 (only for large keyboards).
+5. Trackball module: FR-4, 1.6mm thick, 2 layers, watch soldering orientation, marked CON3.
+6. Scroll wheel: FR-4, 1.6mm thick, 2 layers, recommended encoder height 7mm, button height 6mm, actuation ≤180g, marked CON2.
+7. Direction keys: FR-4, 1.6mm thick, 2 layers, ALPS yellow switches require firm pressing during installation, marked CON4.
+8. Main control board – Left-hand (small): FR-4, 1.6mm thick, 2 layers.
+
+> * The three small control boards are shared across all keyboards: `3-Trackball`, `4-Scroll Wheel`, `5-Direction Keys`.
+> * Both `5-Direction Keys` and `1-Left-hand Soldered (small)` use ALPS yellow switches.
+> * Note: left-hand and right-hand large keyboards are not perfect mirrors.
+> * Trackball uses SPI1 channel; scroll wheel uses two dedicated signal lines, allowing replacement with other devices.
+> * MCU: STM32G431CBU6.
+> * Compatible with both A-to-C and C-to-C cables.
+
+### 3D-Printed Parts:
+
+* Keycaps: resin, PLA, etc.
+* Trackball mount: resin, PLA, etc.
+* Mouse buttons: resin, PLA, etc.
+* Case: resin, PLA, etc.
+* Base: resin, PLA, etc.
+
+### Materials:
+
+* Positioning plate: POM, 1.5mm thick.
+* Positioning plate foam strips: single-sided adhesive.
+* Sandwich foam: PORON, 3.5mm thick.
+* Switch pad foam: 2mm thick.
+* Bottom foam: PORON, 4mm thick.
+* Silicone pad (only for small keyboard): 5mm thick, Shore 00-10 hardness.
+
+### Hardware:
+
+| Component              | Large Keyboard | Small Keyboard |
+| :--------------------- | :------------: | :------------: |
+| M3×3×4 heat-set insert |        8       |        8       |
+| M2×2×3 heat-set insert |        2       |        –       |
+| M2×3×3 heat-set insert |       17       |       12       |
+| M3×6 flat-head screw   |        2       |        6       |
+| M3×15 flat-head screw  |        –       |        4       |
+| M3×22 flat-head screw  |        6       |        –       |
+| M2×8 button-head screw |        4       |        4       |
+| M2×3 button-head screw |        2       |        –       |
+| M2×5 button-head screw |       13       |        8       |
+| M3×16 pan-head screw   |        –       |        2       |
+
+### Other Components:
+
+* Trackball: 25mm diameter, PTFE.
+* Support balls: 2mm diameter, PTFE, 6 pieces installed in the printed trackball holder.
+* Scroll wheel: recommended 19–20mm diameter, 4–5mm thickness, metal.
+* Stabilizers: 2U plate-mount stabilizers.
+* Switches:
+
+  * Small keyboard: 57 ALPS yellow low-profile switches.
+  * Large keyboard: 57 standard mechanical switches.
+* Ribbon cables: 0.5mm pitch, 8-pin reverse, two at 10cm and two at 15cm.
+
+> - All control boards and small boards have CON markings for matching connectors.
+> - For FPC connectors placed on opposite sides, use reverse ribbon cables when all connectors are bottom-facing.
+
+### Exploded Models:
+
+![Small left-hand keyboard exploded](/Docs/Image/左手小键盘爆炸图.jpg "Small left-hand exploded")
+![Large left-hand keyboard exploded](/Docs/Image/左手大键盘爆炸图.jpg "Large left-hand exploded")
+
+### Assembly Order (Large Keyboard Example):
+
+**Pre-assembly steps:**
+
+* Connect the 4 small PCBs to the main keyboard PCB with ribbon cables, flash the firmware.
+* Install 3–5 switches, scroll wheel, and trackball. Check functionality before full assembly.
+* Insert heat-set inserts into the case and base.
+* Print legends on keycaps.
+* Stick foam strips onto positioning plate (both sides).
+
+> For the first firmware flash, press the button labeled **“B”** on the back of the PCB while plugging in the USB cable.
+> To update firmware, hold **ESC** while plugging in USB.
+> See [Flashing Your Keyboard (QMK)](https://docs.qmk.fm/newbs_flashing) for details.
+
+**Assembly steps:**
+
+1. Fix the 4 small PCBs to the base with screws (watch cable orientation). The trackball holder is screwed from below.
+2. Mount the mouse buttons on the keyboard PCB.
+3. Stack layers in this order: bottom foam → switch pad foam → keyboard PCB → sandwich foam → positioning plate.
+4. Insert switches.
+5. Place the case on top and secure with screws.
+6. Install keycaps. Assembly complete.
+
+> Screw and insert installation guide can be found [here](https://github.com/htx-studio/One-Handed-Keyboard/tree/main/Model).
+
+This is our first open-source project. Any feedback or suggestions are welcome. Thank you!
+
+---
+
+## References
+
+[Quantum Mechanical Keyboard Firmware](https://docs.qmk.fm/)
+mrjohnk. ADNS-9800. [GitHub repository](https://github.com/mrjohnk/ADNS-9800/)