LaTeXPAD

LaTeX-PAD: Custom Macropad for Math & Science (RP2040)

This is a custom 15-key macropad with a rotary encoder. I built it mainly to speed up writing math formulas in LaTeX. It runs on a Seeeduino XIAO RP2040 using custom QMK firmware.

I designed this project to make my life easier when typing complex equations. It combines a regular numpad with some really handy LaTeX macros.

Key Features

• 15 Cherry MX-style keys wired in a 4x4 ortholinear matrix.
• 1 Rotary Encoder (EC11) with a push-button switch.
• Smart Cursor Navigation: The macros do the boring work for you. If you paste a command like \frac{}{}, the cursor automatically jumps back inside the first set of brackets so you can start typing right away.
• Seeeduino XIAO RP2040: Has more than enough memory and pins for complex QMK setups.

Hardware & Enclosure

Case Design

I designed the enclosure from scratch in Fusion 360 to securely hold the PCB, switches, and the microcontroller together.

• Optional: The case is 3D printed in [PLA/PETG] and held together with [M3 screws].

PCB

Note: The footprint library in the schematic might show SAMD21 pinouts (D0, D1, etc.). Just ignore that — the actual hardware uses the XIAO RP2040, and the QMK firmware is mapped to the correct RP2040 pins (GP26, GP6, etc.).

Logik

Firmware Details

The macropad runs on QMK Firmware to handle matrix scanning, the encoder, and all the custom macros.

Keymap Layers

• Base Layer (_NUMPAD): Works just like a standard numpad. It also has a dedicated layer-modifier key.
• LaTeX Layer (_LATEX): Hold the modifier key to access 14 of the most common LaTeX commands (\frac{}{}, \sqrt{}, \sum_{}^{}, \int_{}^{}, etc.).

Rotary Encoder

• Rotate Left/Right: Moves the text cursor left or right. It's really useful for tweaking long equations without touching your mouse.
• Press: Acts as a standard Left Mouse Button click.

Bill of Materials (BOM)

If you want to build one yourself, here's what you need:

• 1x Seeeduino XIAO RP2040
• 15x Cherry MX-compatible switches (e.g., Gateron Red)
• 1x EC11 Rotary Encoder
• 15x 1N4148 Diodes
• Custom PCB (Gerber files are in the hardware/ folder)
• 3D Printed case parts

How to Build & Flash

1. Hardware: Get the PCB fabricated using the Gerber files from the hardware/ folder. Solder the diodes, switches, encoder, and the XIAO RP2040.
2. Firmware: * Set up your local QMK environment.
   • Drop the firmware folder from this repo into your qmk_firmware/keyboards/ directory.
   • Compile and flash the board (e.g., run qmk flash -kb latex_pad -km default).