Independent Heading, Variation And Time Source

Heading Module

A good heading source should be quiet, consistent and honest about confidence. This module is built to give the autopilot and the wider NMEA2000 network that stable reference.

Suite Overview Safety + Prevention

Why it is separate from Attitude

The Heading module is a dedicated heading, variation, GPS and time source. The Attitude modules focus on boat motion and wave behavior, while this node keeps the navigation reference clean and predictable.

It combines an RM3100 magnetic sensor, ICM-20948 motion reference, GPS position/time and optional one-pulse-per-second timing. That lets it publish standard NMEA2000 heading, variation, GNSS and time PGNs without depending on the rest of the autopilot core.

Primary Outputs

Magnetic or true heading on standard NMEA2000 PGN 127250.
Rate of turn and basic attitude for consumers that need a compact heading-source motion reference.
Magnetic variation on PGN 127258, derived from WMM2025 when GPS position and UTC time are valid.
GPS position, COG/SOG, GNSS data, system time and date/time PGNs for networks that need a local source.
KSF health, NMEA statistics and magnetic diagnostics for service and integration work.

Magnetic Variation

Variation is not treated as a fixed value unless it has to be. When GPS fix and time are valid, the module evaluates the embedded WMM2025 model for the boat position and date. That result becomes the active variation used for true-heading output and for the published variation PGN.

If WMM2025 is not available yet, the module falls back to the stored manual declination value instead of guessing.

Primary Or Backup Publisher

BACKUP mode suppresses standard outputs when fresh equivalent NMEA2000 publishers are already present.
BACKUP_ATT keeps heading/attitude behavior conservative while still allowing variation, GPS and time outputs to remain useful.
ALWAYS makes the module publish its enabled standard PGNs regardless of other sources.
Freshness tracking prevents the node from fighting a healthy primary source, while still letting it take over when the network needs it.

Commissioning And Calibration

The RM3100 should be mounted away from steel, magnets, loudspeakers and current-carrying cables.
Stationary gyro calibration and magnetic swing calibration are supported locally and from the Main/UI configuration page.
Bad magnetic calibration sweeps are rejected instead of being saved blindly.
Serial diagnostics such as GPS?, MAG?, VAR? and N2K? make bench and boat checks straightforward.

How It Helps Offshore

The practical value is not only another heading number. The module gives the system a clean heading reference, a live variation source, and a disciplined time/GNSS path that can remain useful even when another device on the network is missing, stale or configured differently.

The steering core gets a stable heading source with explicit freshness and publish-policy behavior.
The Attitude pair can focus on motion, wave-phase and prevention cues.
The UI can fetch configuration, run calibration and inspect heading diagnostics through the same Main/UI workflow as the other modules.
For singlehanded sailing, this reduces uncertainty when troubleshooting a heading, time or variation problem at night.

Related across the suite

Current page focus: Dedicated heading, WMM2025 variation, GPS/PPS time and backup-publisher behavior.

RM3100 magnetic heading with ICM-20948 motion reference.

WMM2025 magnetic variation from current GPS position and UTC time.

One-pulse-per-second GPS timing for cleaner system time output.

BACKUP, BACKUP_ATT and ALWAYS publishing modes.

Standard NMEA2000 heading, ROT, variation, GNSS and time outputs.

Main/UI remote fetch, configuration and calibration workflow.

Feedback And Comments

This project is still in progress, and I would genuinely like feedback on what is missing, what feels unclear, and what would be most useful offshore. The first sea trial is planned for the 2026 sailing season, and every comment is reviewed by me before it appears publicly.

No public comments yet. You can be the first to add feedback.

Built For Singlehanded Offshore Reality

These public pages focus on what the suite actually delivers offshore: steadier steering, fail-safe automation, and practical offshore support that reduces workload without taking control away from the skipper.