Firmware for the Hat Labs HALMET board that reads a legacy Raymarine ST60+ wind transducer — the vane and cups at the top of the mast, whose display head died but whose sensor is still healthy — and republishes apparent wind onto the boat's NMEA 2000 backbone.

The story: the ST60+ display head failed; the wind vane 15 m up the mast was fine. Rather than climb the mast or replace the instrument, HALMET taps the old sensor's raw sin/cos and cup-pulse wires directly and puts wind back on the bus.

📖 Project page: https://den200.github.io/halmet-wind-vane/ · 🔌 Wiring & power guide

• V1 (primary): transmits PGN 130306 (Wind Data) every 100 ms (10 Hz) with WindReference = Apparent. This is the deliverable — the boat (Orca Core 2 + N2K displays) consume wind over the wired backbone.
• V2 (secondary): publishes the same calibrated values to SignalK over WiFi (environment.wind.angleApparent / speedApparent), so any SignalK plugin or web app (KIP, Freeboard, instrument panels, loggers) can display them once installed.
• Boat time server: answers NTP on UDP 123 (halmet-wind.local) with the GNSS time from PGN 126992 on the backbone, so computers without a battery clock get the right date at boot, offshore too. Only GNSS-sourced 126992 dated 2026 or later is trusted, two consecutive messages must agree, and it stays silent when it has no fix (or none for 10 min) so clients fall back to their next server. Android: settings put global ntp_server "ntp://halmet-wind.local|ntp://time.android.com".

The vane encodes its angle as two ratiometric voltages (sine and cosine); recovering the angle is atan2(sin, cos). Since atan2 is scale-invariant, calibration only needs to centre each channel — see src/sin_cos_angle_transform.h.

Two details there are deliberate. Smoothing averages the sin/cos vector, not the emitted angle: averaging the angle breaks at the ±π wrap, where samples alternate between ≈ +179° and ≈ −179° and mean to 0°, so dead astern would read as dead ahead. And the no-data check watches the raw terminal voltage (Blue/Green must be inside 2–7 V), not the computed magnitude: an unpowered transducer puts both channels at 0 V, which centres to a large, perfectly steady vector and yields a convincing, unchanging −135°. The gate sits before the smoothing, turning a bad reading into NaN, which clears the averaging window — so nothing from the fault blends into the first angles after recovery. The same 0 V rails also mean the pulse line is dead, so speed goes to no-data as well instead of reporting a false calm.

⚠️ The cheap buck modules ship at ~20 V — set it to 8.0 V on the bench before connecting the sensor, or you'll cook it. Full details in docs/WIRING.md.

Most of the build is reused — the wind vane, its cable, and the boat's NMEA 2000 network are already there. You really only buy two things:

Plus the open-source firmware in this repo.

All tunables persist to flash and are editable at http://halmet-wind.local/:

• Angle offset (offset_rad) — align vane zero to the bow.
• Angle direction (sin_sign) — +1 normal, −1 if wind reads backward.
• Per-channel centring — set each sin/cos midpoint (≈ Vmid).
• Smoothing (samples) — sin/cos samples averaged before the angle is computed; 5 ≈ a 2.5 s window at the ~2 Hz sample rate.
• Speed multiplier K — 0.5144 m/s·Hz⁻¹ for egg-cup ST60+ (~1 kn/Hz), ~0.36 square-cup.

With the mast up, derive the sin/cos centres by ellipse-fit on logged free-rotation data (tools/ellipse_fit.py); trim K against GPS in calm air.

Function 130 (Atmospheric), Class 85 (External Environment), Manufacturer 2046 (unregistered), preferred source address 35.

pio run -e halmet              # build
pio run -e halmet -t upload    # flash over USB (first time only; then OTA, see below)
pio device monitor -b 115200   # serial
tools/run_host_tests.sh        # angle-transform regression tests, on the laptop

src/sin_cos_angle_transform.h is pure math over a thin SensESP base, so it is compiled against minimal stubs in test/host/ and exercised on a laptop — full circle accuracy, behaviour through the ±π wrap, NaN recovery, sign/offset handling and config clamping. No board required.

SensESP v3 on PlatformIO (pioarduino platform), NMEA 2000 via the ESP32 TWAI driver, ADS1115 via Adafruit ADS1X15. Board target esp32dev.

The USB flash is needed once. After that the board updates itself from a browser at http://halmet-wind.local/update (also linked from the config page), over the boat Wi-Fi or the board's own access point:

1. Bump FW_VERSION in src/version.h, commit, tag v<version>, push the tag. GitHub Actions builds and attaches halmet-wind-v<version>.bin (+ .sha256) to a release. It refuses to publish if the tag and FW_VERSION disagree.
2. On the phone, open the update page and press Check latest release. It asks the GitHub API from the browser and links the .bin. If the boat Wi-Fi has no internet, download the file on mobile data first — it lands in Files.
3. Pick the file, press Flash. The board writes it into the spare OTA slot, verifies the image (segment checksums and the SHA-256 the build appends), only then marks it bootable, and reboots. The page waits and shows the new version once it is back. Wind data pauses for about ten seconds.

A truncated or wrong file is refused before the switch — the first bytes are checked for the ESP32 image magic and chip id, and the whole image is verified at the end — so the running firmware keeps running. If a new image ever fails to boot, the bootloader rolls back to the previous slot on the next reset. Calibration and Wi-Fi settings live in their own partition and survive updates.

• On the wire: candump can0,09FD0200:1FFFFF00 on the RPi/MacArthur HAT → a PGN 130306 frame from source 35 every 100 ms.
• SignalK / Orca: apparent wind angle & speed populate and read correctly.

Licensed under the Apache License 2.0 — see LICENSE. This is the same license as the Hat Labs HALMET example firmware and the SensESP framework it builds on, keeping everything license-compatible.

Forked from the structure of the Hat Labs HALMET example firmware; built on SensESP. Not affiliated with Raymarine or Orca. Built with Claude Code.