NMEA 2000 Emitter Cannon

A Signal K plugin that converts Signal K deltas into NMEA 2000 messages: 82 configurable data conversions covering 60 data PGNs, plus the configurable PGN 126464 list broadcast, validated against Canboat definitions and reviewed against model-specific chartplotter receive lists.

Built on the foundation of signalk-to-nmea2000 by Scott Bender and the Signal K community.

What's new in 1.10.3

• Canonical water temperature. environment.water.temperature now has dedicated Sea Temperature conversions for PGN 130316 and PGN 130312. The Environmental preset selects the modern PGN 130316 conversion and leaves obsolete and superseded temperature PGNs as manual compatibility choices.
• Clear Signal K semantics. Fixed input paths are read-only, and the optional publisher control is explicitly labeled as a $source filter. Entering the input path itself in that control is rejected before Save. Publisher lookup failures remain distinct from verified mismatches and offer a Retry action.
• Safer, discoverable mappings. Mapping tables suggest Signal K assets from the server path inventory, distinguish asset presence from required measurement availability, separate Signal K input columns from NMEA 2000 output columns, validate identifiers and instances before Save, and expose configured paths to the Config Advisor.
• Actionable live status. Each conversion distinguishes waiting for input, publisher-filter mismatch, a blocked NMEA 2000 echo, input with no encodable output, stale input, overdue scheduled activity, and active emission. Mapped conversions identify each row and report last-seen input paths separately.
• Accurate validation and diagnostics. Multi-table mapping issues focus the correct row, and unrelated process-wide deltas no longer inflate input or empty-output counters.

See the v1.10.3 changelog entry and the full release history.

What it does

Signal K is an open marine data standard that streams a boat's navigation, environment, and electrical data over a single API. NMEA 2000 Emitter Cannon closes the loop in the other direction: it subscribes to the Signal K paths your boat publishes and re-emits them as NMEA 2000 PGNs through the server's NMEA 2000 output, so chartplotters, instrument displays, and autopilots on the bus see data that originates in Signal K (a weather plugin, a non-NMEA sensor, a computed value) as native bus traffic.

Every conversion is verified round-trip through the canboatjs encoder. Fields, ranges, and enum values follow its bundled Canboat definitions, while transport priorities follow the current stable Canboat 7.1 database. It pairs well with sensor-side plugins such as signalk-virtual-weather-sensors.

Features

• 82 configurable data conversions emitting 60 data PGNs, plus the plugin's configurable PGN 126464 list broadcast and 5 stack-owned bus-layer PGNs (59392, 59904, 60928, 126993, 126996) advertised in that list
• Chartplotter-oriented PGN priorities, SID fields, temperature-source values, and wind and bearing reference enums, with model-specific behavior documented instead of assumed across a vendor's entire product line
• Reactive subscriptions via RxJS 7.8 with debounced multi-key aggregation and per-key freshness timeouts
• Source filtering per conversion: keep the fixed Signal K schema path and optionally choose a specific $source publisher, using consistent exact or dot-prefix matching
• Resend timers for conversions whose values remain current, plus a global default. Event-driven targets, course data, timers, and fixed timestamps are never replayed as fresh data
• Config Advisor (optional): reviews the Signal K paths your boat publishes, recommends which conversions to enable or disable, and flags enabled conversions whose pinned $source has gone stale (a renamed weather provider or a re-enumerated sensor), with optional QuestDB history
• A React configuration panel with dense one-line conversion rows, a single-open inline editor, a compact sticky toolbar carrying catalog search and live status, category tabs with per-category Enable all and Disable all, preset chips, a first-run setup wizard, and shared signalk-nearlcrews-ui controls with Light, Auto, Dark, and red-preserving Night themes
• NMEA 2000 echo guards that use authoritative source metadata to reject known bus-origin input instead of re-emitting it onto the same bus. Unknown origins remain compatible, and a numeric publisher suffix alone is not treated as proof of NMEA 2000 origin
• Strict TypeScript, an ESM plugin bundle, and RxJS as the only runtime dependency
• Embedded canboatjs round-trip tests on every conversion module, plus advisor, lifecycle, panel, and protocol-boundary unit tests

Screenshots

| Conversion config | Environment category | Config Advisor | | :---: | :---: | :---: | | | | |

Requirements

• Signal K server 2.x. The React config panel loads on every signalk-server 2.x admin UI.
• A browser with native CSS @scope support: Chromium or Edge 118, Firefox 146, or Safari 17.4 and newer.
• Node.js 22.18 or newer.
• A supported NMEA 2000 gateway (for example an Actisense NGT-1 or a Yacht Devices YDNR-02) connected so emitted messages reach the bus.

Installation

Install from the Signal K admin UI under AppStore, then Available, or from npm:

cd ~/.signalk
npm install signalk-nmea2000-emitter-cannon

From source:

git clone https://github.com/NearlCrews/signalk-nmea2000-emitter-cannon.git
cd signalk-nmea2000-emitter-cannon
npm install
npm run build
ln -s "$(pwd)" ~/.signalk/node_modules/signalk-nmea2000-emitter-cannon

Configuration

In the Signal K admin UI, open Server, then Plugin Config, find "NMEA 2000 Emitter Cannon", and enable the plugin. The plugin ships a React config panel that the Signal K admin loads via webpack 5 Module Federation. The panel has these areas:

1. Sticky toolbar: catalog search, a condensed status chip (NMEA 2000 output readiness, count of enabled vs total conversions, a stale-poll marker, and a jump-to-error button), the Configure and Status toggle, the theme toggle, and the Setup wizard shortcut. It stays pinned as you scroll.
2. Config Advisor (optional, collapsed by default): reviews the Signal K paths your boat publishes, recommends which conversions to enable or disable, and flags enabled conversions whose pinned $source has gone stale. Its settings sub-panel covers QuestDB history and a periodic review schedule, each control with inline help.
3. Preset chips (collapsed by default): Basic Navigation, Engine Set, Full AIS, Environmental, Raymarine. Click a chip to enable the tagged conversions in one action; presets are additive.
4. Global resend interval (seconds, collapsed by default): default cadence for every conversion whose own resend is 0. Default 5; set to 0 to disable global resend.
5. Category tabs (Navigation, Engine, Electrical, Tanks, Environment, AIS, Comms, System), each listing its conversions as dense one-line rows with per-category Enable all and Disable all controls. The toolbar's catalog search filters by title, PGN number, and Signal K path across all categories.

Each conversion row shows an enable checkbox, the title and PGN run, an error glyph, and a specific live state such as waiting for Signal K input, publisher filter mismatch, input with no encodable output, or active emission. Clicking a row opens its editor inline below it (opening another row closes the previous one). Fixed-path conversions show the read-only Signal K input path, an optional Signal K publisher ($source) filter, and separate NMEA 2000 output controls. Mapping tables group their Signal K input and NMEA 2000 output columns, suggest asset ids found in the server path inventory, check for the measurements each conversion needs, and block Save when an enabled mapping is invalid. The inventory refreshes automatically and also provides visible Refresh and Retry controls. Optional per-path publisher pins follow the mapping in a collapsed Advanced publisher filters section. Mapping editors cover conversions that need explicit Signal K paths, identifiers, NMEA 2000 instances, or field options (BATTERY, ENGINE_PARAMETERS, EXHAUST_TEMPERATURE, TANKS, SOLAR, AC_STATUS, CHARGER_STATUS, INVERTER_STATUS, VESSEL_TRIP, RAYMARINE_BRIGHTNESS, NOTIFICATIONS, TEMPERATURE_*).

Signal K paths are schema-defined data identities, not user-facing labels. For example, environment.outside.temperature is outside air temperature, while environment.water.temperature is water temperature. The publisher field is only a filter on the update's $source; it cannot redirect one path to the other. The panel blocks a publisher filter that repeats its own input path. Use TEMPERATURE2_SEA for modern PGN 130316 water temperature, or the manual TEMPERATURE_SEA compatibility conversion for PGN 130312.

The config panel loads on any signalk-server 2.x admin UI. v1.4.x config payloads migrate transparently the first time the panel loads them.

Vessel Trip estimates

VESSEL_TRIP is disabled by default. In its mapping editor, add every fuel tank that supplies the selected engines, using its canonical tanks.fuel.<id> Signal K path, then add every consuming engine by the identifier used under propulsion.<id>. The plugin emits remaining fuel only after every configured tank has a current value. It adds time to empty only when every configured engine has a current fuel rate, and adds distance to empty when current speed over ground is also available.

For a Raymarine Fuel Manager display, also configure the chartplotter's fuel settings and provide PGN 127489 or 127497 for fuel consumption, plus PGN 129026 with GNSS for distance to empty. Enable ENGINE_PARAMETERS or ENGINE_TRIP, plus COG_SOG, when this plugin must provide those supporting messages. Other chartplotters have model- and firmware-specific requirements. See the PGN reference for the calculation, freshness behavior, limitations, and current compatibility notes.

Documentation

• PGN reference: all 61 plugin PGNs, conversion modules, bus-layer PGNs, and chartplotter guidance
• Troubleshooting
• Development guide
• Changelog
• Contributing
• Security policy

Development

The published plugin and development toolchain require Node 22.18 or newer. The repository pins Node 22.18 and npm 11.18, while CI verifies on Node 24. CanboatJS and @canboat/ts-pgns are exercised in the test suite and are not runtime dependencies. signalk-nearlcrews-ui is bundled into the panel as a pinned development dependency, while React remains supplied by Signal K Admin.

git clone https://github.com/NearlCrews/signalk-nmea2000-emitter-cannon.git
cd signalk-nmea2000-emitter-cannon
npm install
npm run hooks        # one-time: enable the pre-commit hook
npm run build        # esbuild plugin bundle plus webpack panel
npm test             # Vitest suite
npm run check        # type-check the plugin, the panel, and the tests
npm run lint         # code, Markdown, and spelling checks
npm run format       # Biome auto-format
npm run verify       # local full verification gate

The repository-owned pre-commit hook runs formatting, lint, architecture, and dead-code gates. The pre-push hook runs npm run verify serially. Run npm run verify:release before preparing a release. See the development guide for the full workflow.

License

Apache-2.0: see LICENSE for the full text. The software is provided "AS IS", without warranty of any kind. Data this plugin places on the NMEA 2000 bus is advisory: always carry independent means of navigation and verify against your primary instruments.

Acknowledgments

Built on the foundation of signalk-to-nmea2000 by Scott Bender and the Signal K community. Full credit to the original authors for the conversion framework and PGN implementations. NMEA 2000 Emitter Cannon is written and maintained by Nearl Crews.

• Signal K Project for the open marine data standard
• Canboat Project for the NMEA 2000 protocol implementation that the canboatjs encoder is built on

NMEA 2000 Emitter Cannon pairs well with sibling plugins such as signalk-virtual-weather-sensors, signalk-openrouter-companion, and signalk-crows-nest.

Support

Find this plugin useful? You can support its continued development by buying me a coffee.

• Report a bug
• Request a feature
• Security issues