Recorder

pixel-snap-voice

A one-off slim rectangular voice-note recorder that snaps to the back of a Google Pixel 10 using Pixelsnap / Qi2 magnets (MagSafe-style accessory rings work). It records raw WAV files, charges and dumps data over USB, can share those files over its own Wi-Fi network, and leaves transcription to a computer.

This repo holds hardware, firmware, simulation, and (later) a local transcription helper. The first board is meant to be ordered from quick-turn services after the sims pass — not invented from unsolved problems.

What it is

• ESP32-S3-MINI-1U, ES8311 codec (I2S master), analog MEMS mic, class-D speaker (or headphone jack if thickness loses)
• 16-bit PCM WAV, 48 kHz mono (~173 MB/hour)
• USB Mass Storage when plugged into a computer
• Wi-Fi share: the recorder makes its own WPA2 network and serves /recordings in a browser (and read-only WebDAV)
• No on-device transcription, no Bluetooth file transfer, no wireless charging through the accessory

MCU choice and why we did not switch off Espressif: docs/audio-platform.md.

Repo layout

Set up a machine

The hardware checks need KiCad 10 (kicad-cli plus its pcbnew Python module), the host sim needs CMake and a C compiler, the power-path sim needs ngspice, and route_pcb.py needs the freerouting autorouter.

Ubuntu 24.04 (a dev box, CI runner, container, or a cloud coding agent): from the repo root, run

bash scripts/setup-ubuntu.sh

It installs build-essential, CMake, ngspice, KiCad 10 from the official KiCad PPA, and freerouting 2.4.1 into /opt/freerouting, then builds the host sim into build/host. It is safe to run again. It uses sudo for apt unless it is already root. For a cloud agent or CI job, make that command the environment's setup or install step.

Windows or macOS: there is no script. Install by hand:

• KiCad 10. Run the pcbnew scripts (generate_pcb.py, route_pcb.py, check_placement.py) with KiCad's bundled python, not system Python.
• CMake and a C compiler (MSVC, MinGW, or clang).
• ngspice, only for the power-path sim.
• freerouting, only for route_pcb.py. Put it on PATH, unpack it to ~/.local/opt/freerouting/, or set PSV_FREEROUTING to the launcher.

Python packages are in requirements.txt: numpy (for route_pcb.py) and cadquery (only for the metal tray STEP). Install them into a virtual environment made with --system-site-packages, so KiCad's pcbnew stays importable. The file also lists what comes with KiCad and Blender instead of pip.

Firmware needs ESP-IDF on top of this. See firmware/README.md.

Simulate first

From the repo root, with CMake and a C compiler (MSVC, MinGW, or clang):

cmake -S sim/host -B build/host
cmake --build build/host
./build/host/recorder_test      # Windows: build/host/Debug/recorder_test.exe
./build/host/recorder_sim

Mechanical keepouts (Python 3, no extra packages):

python hardware/cad/check_envelope.py

Power path (needs ngspice):

ngspice -b sim/spice/power_path.cir

Physical phases

0. Prove capture and playback on an Espressif voice board (Korvo-2 / ESP-BOX) or OpenMic; Sense is recorder-core only. See docs/phase0-bringup.md.
1. Custom slim PCB + 3D-printed chassis + bought magnet ring (JLCPCB).
2. Same PCB in CNC 6061 aluminum (not steel).

After you change the product schematic sources, run python hardware/kicad/recorder/generate_recorder.py then python hardware/kicad/recorder/verify_schematic.py. That overwrites sheets only. It does not write recorder.kicad_pcb. Edit the board (or rebuild it on purpose with generate_pcb.py) until traces and DRC are clean. Do not order boards until python scripts/check_gates.py is clean and kicad-cli pcb drc is clean and kicad-cli has written Gerbers from hardware/kicad/recorder/recorder.kicad_pcb.

Transcription

Dump WAVs over USB, then run a local model (whisper.cpp) on the computer:

python software/transcribe.py /path/to/recordings/20260828-181742.wav