A compact 15-key USB shortcut keyboard designed to trigger shortcuts in CAD software.
Built around a Seeed XIAO RP2040 (DIP version) using a 3×5 diode-protected key matrix (anti-ghosting).

This repo contains the full hardware + firmware stack: schematic, PCB layout, assembly references, and firmware that sends USB key events to the computer.

• PCB/: KiCad project files (schematic + PCB layout)
• Firmware/: firmware source code
• docs/: screenshots used in this README

CAD workflows rely heavily on shortcuts (sketch tools, constraints, navigation, etc.). A full keyboard works, but it increases hand travel and breaks focus. This small keyboard provides 15 dedicated keys mapped to the most-used CAD actions.

• 15 keys total
• 3 rows × 5 columns matrix
• 1 diode per key (ghosting prevention)
• USB connection via XIAO RP2040
• Optional per-key RGB backlight (SK6812 addressable LEDs)
• PCB constrained to ≤ 100 mm × 100 mm

The keys are wired as a matrix to reduce GPIO usage:

• Rows configured as outputs
• Columns configured as inputs with pull-ups
• Each key uses one series diode to prevent ghosting during matrix scanning

Electrical structure per key:

ROW → diode → switch → COLUMN

Diode orientation rule used in this design:

• Diode stripe faces the row net (cathode on the row side)

This allows columns to be pulled low when a row is driven low and a switch is pressed.

• LEDs powered from USB 5V (VBUS) and GND
• Data from a free GPIO (example: GPIO3) into LED1 DIN
• Daisy-chain DOUT → DIN across all 15 LEDs

• Key spacing: 19.05 mm center-to-center (standard MX spacing)
• Board outline designed to fit within the 100×100 mm maximum
• Switch footprint: SW_Cherry_MX_1.00u_PCB
• LEDs placed near each switch footprint (outside switch courtyard)
• Diodes placed close to switches (can be bottom-side to free space and simplify routing)

1. Solder the diodes (verify stripe orientation toward row nets)
2. Solder the SK6812 LEDs (optional; verify DIN/DOUT direction)
3. Solder the Seeed XIAO RP2040 module
4. Solder the MX switches
5. Flash the firmware
6. Connect over USB and validate key presses and shortcuts

Firmware location:

Firmware/main.py

This project uses CircuitPython with a KMK-style approach (single main.py).
The firmware scans the 3×5 matrix and sends USB keyboard events to the host computer. Keys are currently mapped to placeholder shortcuts that can be replaced with the exact shortcuts used by your CAD tool.

Typical categories to map:

• Sketch tools (line, rectangle, circle)
• Constraints (coincident, parallel, perpendicular)
• Navigation (pan, zoom, rotate, view presets)
• Editing (copy, paste, undo, redo)
• Utilities (measure, save)