RetroMeshDevice

An off-grid handheld communicator built for the Meshtastic Build-Off 2026 hardware competition.

The goal is to build a standalone device that runs Meshtastic natively, using an ESP32-S3 and a custom 12-button T9 physical keypad (driven by an MCP23017 I/O expander).

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📖 What this project does

RetroMeshDevice (RMD) is a custom-built, standalone Meshtastic node in a retro phone form factor. Unlike phone-paired setups, it's a self-contained device with its own screen, keypad, battery, and LoRa radio built from scratch around a T9 physical keypad instead of a touchscreen or QWERTY layout.

It's designed as an alternative for people who want a dedicated, pocketable Meshtastic node without depending on a smartphone to configure, send, or read messages

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I am documenting the entire design and assembly process step-by-step on my blog:

• Part 1 (Schematic & Design): myembeddedstuff.com/meshtastic-build-off-2026-retromeshdevice
• Part 2 (PCB Assembly): myembeddedstuff.com/meshtastic-build-off-2026-pcb-assembly
• Part 3 (Firmware Validation & Power Consumption): myembeddedstuff.com/meshtastic-build-off-2026-hardware-bring-up

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📂 Repository structure

• /case — 3D printable case STEP file.
• /hardware — Schematic diagrams and Bill of Materials (BOM).
• /firmware — Firmware source code and utilities:
  • /Meshtastic — Custom Meshtastic variant for this board, ready to compile.
  • /Test — Standalone hardware self-test firmware for quick board bring-up validation.
  • /Bin — Precompiled binary (Meshtastic v2.8).
• /images — Project photos and renders.

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🔗 How it uses Meshtastic

RetroMeshDevice runs a custom Meshtastic firmware variant rather than stock Meshtastic, because out-of-the-box Meshtastic firmware doesn't support the MCP23017 I/O expander that drives this board's T9 keypad.

To make this work, I implemented a full MCP23017 keyboard driver for the Meshtastic firmware (interrupt handling, key debounce/multi-tap/long-press logic, I2C device detection) and submitted it upstream:

👉 meshtastic/firmware PR #11015 — feat: add driver for MCP23017

Until this PR is merged into the official Meshtastic repository, you'll need to apply these changes manually (see Installation below).

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🚀 Installation & running

1. Clone the official Meshtastic firmware repo:

   git clone https://github.com/meshtastic/firmware.git
   cd firmware

2. Add MCP23017 support:

   • Check if PR #11015 has already been merged into develop.
   • If merged: skip to step 3.
   • If not merged yet: copy over the modified files from that PR into your local clone (src/detect/ScanI2C.*, src/detect/ScanI2CTwoWire.cpp, src/input/MCP23017Keyboard.*, src/input/cardKbI2cImpl.cpp, src/input/kbI2cBase.*, src/main.cpp).

3. Add the board variant:

   • Copy the contents of this repo's /FW_Meshtastic folder into the corresponding variants/ folder of your Meshtastic firmware clone.

4. Build and flash:

   pio run -e retroMeshDevice -t upload

This compiles the firmware for the retroMeshDevice environment and uploads it directly if the board is connected via USB.

5. Alternative — use the precompiled binary:

   • If you don't want to build it yourself, a precompiled binary (Meshtastic v2.8) is available in /Bin.

6. Quick hardware test (optional):

   • Before flashing full Meshtastic firmware, you can validate the board itself using the standalone self-test firmware in /FW_TEST — it checks the buzzer, battery ADC, MCP23017/keypad, OLED, and SX1262 radio.

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🏆 Support the project!

This project is officially entered in the contest. If you like the design, please drop a reaction (like a 👍 or ❤️) on the official submission entry here:

👉 Seeed Studio Build-Off Entry #10

📜 License

This project (hardware design and firmware) is licensed under the GNU General Public License v3.0 — see LICENSE for the full text.