signalk-to-nmea0183

Signal K server plugin that converts Signal K deltas into NMEA 0183 sentences and publishes them on the server's TCP NMEA 0183 port (10110 by default). A per-sentence throttle lets you cap the emission rate in milliseconds so downstream NMEA 0183 consumers don't get flooded.

Installation

Through the Signal K server admin UI — App Store → search for signalk-to-nmea0183 → install. Or from the command line in your ~/.signalk dir:

npm install @signalk/signalk-to-nmea0183

Requires signalk-server with Node >=22.

For NMEA 2000 AIS → NMEA 0183 conversion use signalk-n2kais-to-nmea0183 instead. This plugin does not emit AIS sentences.

Usage

1. Enable the plugin in the server admin UI (Server → Plugin Config → Convert Signal K to NMEA0183) and add a row per sentence you want emitted. Each row shows the required Signal K paths with live availability icons (✅ has data, ❓ value is null, ❌ not present) so you can see at a glance what is wired up.
2. Connect any NMEA 0183 client (OpenCPN, kplex, netcat, ...) to localhost:10110 — the server's built-in TCP NMEA 0183 server.

Per conversion you can optionally set:

• Minimum interval (ms) to throttle high-frequency sentences (0 emits on every source update).
• Custom event name to route a sentence to an extra event in addition to the standard nmea0183out. Useful for piping a single sentence to a dedicated serial port (see Serial output).

If the TCP server is off, enable it in Server → Settings → Interfaces → nmea-tcp. No restart needed.

Supported sentences

Each sentence is independently toggleable and has its own throttle (ms). Leave the throttle at 0 to emit on every source update.

Course and waypoints

• APB — autopilot info, magnetic bearings (--true variant also available)
• BWC — bearing and distance to waypoint
• RMB — recommended minimum navigation info to waypoint
• XTE — cross-track error (-GC great-circle variant also available)

The waypoint identifier in these sentences is taken from the name the Signal K server publishes on the active destination (the server supplies its own WP<n> / DP / VP defaults). Servers that support waypoint naming fill it; older servers leave the identifier fields empty.

Position, heading, speed

• GLL — geographic position, lat + lon
• HDG / HDM / HDMC / HDT / HDTC — heading variants (true / magnetic / deviation-corrected / magnetic-computed-from-true / true-computed-from-magnetic)
• ROT — rate of turn
• RMC — recommended minimum navigation data
• VHW — speed and heading through water
• VTG — track made good and speed over ground
• VLW — cumulative / trip log

Depth

• DBK / DBS / DBT — depth below keel / surface / transducer
• DPT — depth + transducer offset (-surface variant references water surface)

Wind

• MWD — true wind direction + speed (reference: north)
• MWV — apparent (MWVR) and true (MWVT) wind relative to the vessel
• VWR / VWT — legacy relative / true wind angle + speed
• VPW — speed parallel to wind

Environment

• MMB — barometric pressure
• MTA — air temperature
• MTW — water temperature
• XDRBaro / XDRTemp / XDRNA — transducer readings for barometric pressure, air temperature, and pitch + roll (XDRNA)

Rudder and time

• RSA — rudder sensor angle
• GGA — GPS fix data with time
• ZDA — UTC date/time and time-zone offset

Proprietary

• PNKEP01 / PNKEP02 / PNKEP03 / PNKEP99 — NKE Marine Electronics performance sentences: target polar speed, course on the other tack, polar speed + VMG + optimum angle, debug
• PSILCD1 — polar speed + target wind angle for Silva / Nexus / Garmin displays
• PSILTBS — Garmin proprietary target boat speed

Serial output

By default the converted NMEA 0183 stream is served on TCP port 10110 only. To push it out of a serial port instead, configure the serial connection as an NMEA 0183 provider in the admin UI, then add a toStdout: "nmea0183out" line to the provider's subOptions in settings.json:

{
  "pipedProviders": [
    {
      "id": "serial-out",
      "enabled": true,
      "pipeElements": [
        {
          "type": "providers/simple",
          "options": {
            "logging": false,
            "type": "NMEA0183",
            "subOptions": {
              "type": "serial",
              "device": "/dev/ttyUSB0",
              "baudrate": 4800,
              "providerId": "serial-out",
              "toStdout": "nmea0183out"
            },
            "providerId": "serial-out"
          }
        }
      ]
    }
  ]
}

The plugin emits each converted sentence as an internal event named nmea0183out; toStdout wires that event stream into the serial writer.

Contributing

Issues and pull requests welcome at SignalK/signalk-to-nmea0183. npm test runs the full mocha suite; npm run typecheck + npm run build guard the TypeScript surface; npm run mutation runs Stryker against the encoders.

Adding a new sentence is a three-step change documented at the top of src/sentences/index.ts: create a SentenceEncoderFactory-shaped module under src/sentences/, import it in the barrel, add tests under test/. test/registry.ts asserts barrel-vs-directory parity so a missing import fails CI.

License

Apache-2.0. See LICENSE.