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openscribe/hardware/BOM.md
Laurence 031074c9a9
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scaffold: OpenScribe open-source self-hosted AI voice recorder 
Bootstrap of the project (M0). Sets up the monorepo, design docs, hardware BOM,
the open API contract, component skeletons, licensing and CI, following the
Default Workflow SOP.

What changed:
- CLAUDE.md + docs/: copied the Default Workflow so sessions load the SOP.
- state/: PROJECT, ARCHITECTURE, DECISIONS, TODO, NOTES filled in for OpenScribe.
  ARCHITECTURE captures the four-part design (firmware, server, app, case) and the
  three sync paths; DECISIONS records the hardware, AI-stack, storage, app and
  licensing choices; TODO lays out milestones M1-M9.
- hardware/BOM.md: two build options (compact XIAO ESP32-S3 Sense; dev ESP32-S3 +
  I2S mic + SD), wiring/pinout, indicative cost.
- api/openapi.yaml: the completely open API (device + server surfaces), including
  recording list/download/delete and exports (wav/ogg/txt/srt/vtt/md/json).
- firmware/: PlatformIO ESP32-S3 project, two board profiles, pin map, boot scaffold
  with module seams for M1-M4.
- server/: FastAPI skeleton mirroring the OpenAPI, config for self-hosted MinIO,
  faster-whisper and Ollama; stub routes browsable at /docs.
- app/, case/: Flutter app plan; parametric OpenSCAD enclosure.
- Licensing: GPL-3.0 (code), CERN-OHL-S-2.0 (hardware), CC-BY-SA-4.0 (case/docs),
  REUSE-style LICENSES/ with SPDX headers; LICENSING.md explains the split.
- CI: Forgejo Actions workflow builds firmware (both profiles) and lints/imports server.

Why:
- Everything self-hosted and openly licensed per the user's requirements: an open
  API, three sync paths (BLE control, WiFi transfer, independent WiFi upload on
  charge to generic cloud storage), and a full self-hosted transcription+summary stack.

Notes:
- No custom PCB in v1; off-the-shelf modules. Physical verification waits on parts.
- Component code is stubs at M0; features land milestone by milestone, each as its
  own branch/PR per the workflow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-03 10:21:37 +01:00

5 KiB
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Hardware - Bill of Materials and wiring

OpenScribe v1 is built from off-the-shelf modules (no custom PCB). There are two build options: a compact build for a wearable, and a breadboard/dev build that is easier to bring up and debug. Pick one; the firmware and case are parametric to suit either.

Build A - Compact (recommended for the wearable)

Uses the Seeed Studio XIAO ESP32-S3 Sense, which puts the MCU, PSRAM, a microphone and a microSD slot on a thumb-sized board. Fewer wires, smallest case.

# Part Spec / why Qty Notes
1 Seeed XIAO ESP32-S3 Sense ESP32-S3, 8 MB PSRAM, 8 MB flash, WiFi + BLE 5, onboard PDM mic + microSD slot, USB-C, LiPo charge circuit 1 The mic + SD + charger are already on the "Sense" expansion board
2 microSD card 16-32 GB, Class 10 / A1 1 FAT32
3 LiPo battery 3.7 V, 400-600 mAh, JST-PH 1.25 mm 1 Fits the XIAO battery pads
4 Tactile button momentary, 6 mm 1 Record start/stop, long-press = pair/config
5 Status LED XIAO onboard user LED (or add 1 external + resistor) 1 Optional external RGB for richer status
6 (optional) Vibration motor coin ERM + driver transistor 1 Haptic feedback like a NotePin
7 (optional) Slide switch SPDT, for hard power cut 1 In line with the battery

Notes on Build A:

  • The XIAO Sense onboard mic is PDM, not I2S. The firmware supports both; PDM keeps the compact build to one board. For best audio quality use Build B with an I2S MEMS mic.
  • USB-C present = "on charge / hard-powered"; the firmware reads VBUS to switch to the independent WiFi upload mode.

Build B - Dev / best audio (breadboard or protoboard)

Discrete modules, easiest to probe, best microphone.

# Part Spec / why Qty Notes
1 ESP32-S3 dev board with PSRAM e.g. ESP32-S3-DevKitC-1 N16R8 (16 MB flash, 8 MB PSRAM), WiFi + BLE 5, USB 1 PSRAM is required for audio buffering
2 I2S MEMS microphone INMP441 (default, cheap) or ICS-43434 (better SNR ~65 dB) 1 Digital I2S, clean audio, no analogue front-end
3 microSD breakout SPI or SDMMC (1-bit) microSD module 1 SDMMC 1-bit is faster if pins allow
4 microSD card 16-32 GB, Class 10 / A1 1 FAT32
5 LiPo battery 3.7 V, 500-1000 mAh, JST 1 Bigger cell OK on the dev build
6 LiPo charger + protection TP4056 with DW01 protection module (USB-C), or MCP73831 1 STAT pin -> GPIO to detect charging
7 Boost/regulator only if the board lacks a suitable 3V3 LDO from battery 0-1 Most dev boards handle this
8 Tactile button momentary, 6 mm 1 Record start/stop, long-press = pair
9 RGB status LED common-cathode or WS2812 1 Idle / recording / uploading / error states
10 (optional) Vibration motor + transistor coin ERM + 2N2222/AO3400 + flyback diode 1 Haptic feedback
11 Wires / protoboard / headers - - For bring-up

Pinout (default, Build B - ESP32-S3)

These are the firmware defaults; all are overridable in firmware/include/pins.h (added in M1). Avoid strapping pins (0, 3, 45, 46) and USB pins (19, 20).

Signal ESP32-S3 GPIO Notes
I2S mic BCLK (SCK) 4 to mic SCK
I2S mic WS (LRCL) 5 to mic WS
I2S mic SD (DOUT) 6 mic data out -> ESP32 in
I2S mic L/R select GND selects left channel (mono)
microSD CLK 12 SPI SCK (or SDMMC CLK)
microSD CMD/MOSI 11
microSD D0/MISO 13
microSD CS (SPI) 10 SPI mode only
Record button 7 active-low, internal pull-up, other side to GND
Status LED (WS2812 data) 48 or plain LED via 330R on any free GPIO
Charger STAT (charging?) 14 input, from TP4056 STAT (open-drain)
VBUS present (on-charge) 15 via divider from 5V USB, or board VBUS sense
Vibration motor (optional) 16 via transistor

For Build A (XIAO Sense) the mic is PDM and the microSD uses the Sense board's fixed pins; the firmware ships a XIAO pin profile so no manual wiring table is needed.

Power and modes

  • Portable (battery): low-power; record on button; BLE advertising; WiFi on demand.
  • On charge / hard-powered: detected via VBUS/STAT; device joins configured WiFi, runs the REST API on the LAN, and uploads new recordings to the configured object store.

Rough cost (indicative, GBP)

  • Build A (compact): XIAO ESP32-S3 Sense ~£14, microSD ~£5, LiPo ~£5, button/bits £3. **£27** plus a printed case.
  • Build B (dev): S3 devkit ~£10, INMP441 ~£4, SD module ~£3, TP4056 ~£2, LiPo ~£6, LED + button + wires £5. **£30** plus a printed case.

Assembly

Wiring diagrams and assembly photos are added alongside the case in milestone M8. Until then this table plus firmware/include/pins.h is the source of truth for connections.