hardware

# Hardware reference The single source of truth for what's in the box and how it's wired. Mirrors `docs/hardware.md` and `docs/wiring.md`; keep them in sync. ## Bill of materials | Part | Notes | |---|---| | **Seeed XIAO ESP32-C3** | Tiny, USB-C, cheap, has LiPo charger. Alternative: ESP32-C3-DevKitM-1 | | **Adafruit BNO085 breakout** (PID 4754) | Qwiic/STEMMA-QT + headers, 3.3 V, I²C addr 0x4A (default) or 0x4B | | 4-wire Qwiic/STEMMA-QT cable | JST-SH, saves soldering | | USB-C cable (short, marine-grade if routed outside) | | | Enclosure (TBD) | IP65+, non-ferrous, no lid over the antenna | | 3M VHB or M3 fasteners | For a rigid mount — not zip ties, not velcro | Draft — finalize after first prototype. ## ESP32-C3 pinout (XIAO variant) | XIAO pin | GPIO | Used for | Notes | |---|---|---|---| | D4 | GPIO6 | I²C SDA | default for Arduino-ESP32 on C3-XIAO | | D5 | GPIO7 | I²C SCL | | | D1 | GPIO3 | BNO085 INT (optional) | data-ready interrupt, reduces I²C polling | | D0 | GPIO2 | BNO085 RST (optional) | hard reset on wedge | | 3V3 | — | BNO085 VIN | do not wire 5 V even if the breakout has a regulator | | GND | — | BNO085 GND | | **On DevKitM-1** the same functions map differently — check the silkscreen. I²C bus numbers and pins are config, not constants; `lib/config/` loads them from NVS. Don't hardcode `Wire.begin(SDA, SCL)` anywhere but `lib/imu/`. ## I²C wiring ``` ESP32-C3 BNO085 3V3 ──────────────── VIN GND ──────────────── GND SDA (D4/GPIO6) ───── SDA SCL (D5/GPIO7) ───── SCL GPIO3 ─────────────── INT (optional, pull-up on BNO side) GPIO2 ─────────────── RST (optional, active-low) ``` - I²C pull-ups: the Adafruit breakout has 10 kΩ on SDA/SCL. Do not add more - Bus speed: 400 kHz (`Wire.setClock(400000)`). The BNO085 handles 1 MHz, but 400 kHz leaves headroom for cable length in the boat environment - Cable length: keep I²C under 30 cm. For longer runs, put the sensor and ESP32 in the same enclosure and run USB (data) / wifi (no data) to it ## Power - USB-C from a 5 V source (helmlog Pi USB port, a DC-DC from the boat's 12 V, or a small LiPo on the XIAO's onboard charger) - **Power draw**: ~80 mA continuous at 100 Hz sampling + active wifi. LiPo sizing if ever needed: 1000 mAh = ~12 h runtime - **Brown-out**: the ESP32-C3 brown-out detector is enabled by default. If the device resets mid-race on heavy wifi transmit, the USB source is sagging — use a better cable / closer source, don't disable the BOD ## Mounting The sensor should be: 1. **Rigidly bolted** to structure, as close to the boat's pitch/roll center as practical. Near the mast step is ideal; a cabin bulkhead is acceptable; a stanchion base is **not** (flex = noise) 2. **Not near a compass** (Raymarine/B&G fluxgate) — the ESP32 wifi radio can disturb nearby compasses. Minimum 1 m 3. **Not inside a Faraday cage** — keep the wifi antenna end of the XIAO exposed. No metal enclosure lid above the antenna 4. **Orientation is arbitrary** — we handle it via `mount_quat`. Mount it however the wiring wants; just *don't move it* after calibrating ## Test / debug harness For bench development without the boat: - A foam-core L-bracket that holds the device and a laser pointer mounted in a known orientation — lets you rotate through known angles and verify quaternion output - `scripts/fake_device.py` runs on Mac and posts synthetic batches to the helmlog dev instance without any hardware, for server-side development - `scripts/replay_capture.py` takes a saved LittleFS ring buffer dump and replays it to the endpoint at real time or 10×, for reproducing analysis bugs from known data ## Known gotchas - **Two BNO085s on the same bus** — avoid. The breakout can be jumpered to 0x4B but the sh2 library is not designed for multi-instance use - **USB to a Pi** can cause ground loops if the Pi and the device share power via other paths (e.g., both grounded to the same 12 V rail). Symptom: garbled I²C, random resets. Fix: USB isolator or powered hub - **STEMMA-QT cable polarity** — Qwiic/STEMMA-QT is polarized and you can't insert it wrong, but JST-SH to loose headers IS reversible. Check 3V3 and GND before first power-on; reversed polarity kills the BNO085 - **C3 wifi and BNO085 on the same board** — no known interference, but keep the BNO085 > 2 cm from the ESP32-C3 antenna just in case