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NMEA Combiner / Multiplexer
Standard model


The Brookhouse standard NMEA Combiner / Multiplexer combines NMEA 0183 data from up to four marine instruments ( NMEA-talkers ) into a single data-stream for output to a computer port, chartplotter or other  “ NMEA listener ”, such as a repeater instrument or auto pilot. A configurable fifth input port is available for connecting computer or chartplotter output or another NMEA data source.

The Brookhouse multiplexer is an essential component for the integration of  instrument/computer systems on board pleasure boats and commercial vessels. Versatility, functions and price/performance are unmatched by any other comparable products.

All Brookhouse NMEA Multiplexers use the same micro-processor and well-proven software. The multiplexer NMEA input ports are opto-isolated and RS232, USB (optional) and RS422 output ports are available for the connection of computer, autopilot, repeaters and other NMEA listeners. 

With AIS (Automatic Identification System) receivers and transponders now frequently used,  also on pleasure boats, the ability to combine standard low speed NMEA talk ers and high-speed AIS in one data-stream has become an important requirement. The Brookhouse standard multiplexer model supports connection of AIS receivers via a configurable (5th) input port. However, if besides AIS support, the multiplexer is also required to process return data from a computer or chart plotter, typically to feed an autopilot for steering to a waypoint or along a route, we recommend using one of the new Brookhouse multiplexer models with baudrate conversion (models AIS and AIS-C).  

The standard model Brookhouse NMEA Multiplexer is very affordable, but loaded with useful features, including NMEA filtering and "on the fly" editing and including the "GPS backup switch" feature. Seatalk support is available as an optional extra. In Seatalk-mode, channel 1 is connected to the Raymarine Seatalk bus. Data from Seatalk marine instruments is converted into standard NMEA format and is output via the RS232 and RS422 output ports together with NMEA data from other instruments, connected to the 3 other channels. In this mode, the Brookhouse Multiplexer is effectively both a NMEA multiplexer and Seatalk bridge. The Seatalk page contains detailed information about the Seatalk Option for Brookhouse NMEA Multiplexers.

The Brookhouse NMEA Multiplexer uses the latest microcontroller technology which requires a minimum of components. This makes the device reliable and low cost. Smart firmware to manage and buffer the NMEA data ensures high efficiency and data-integrity.

Operation of the unit is fully automatic. When power is switched on, it starts acquiring data and starts outputting the combined data via the output-ports.

Other Brookhouse NMEA multiplexer models are:

Model NMUX-R 

Why a NMEA Multiplexer?

The most basic application of the standard Brookhouse NMEA  multiplexer is combining output of two or more marine instruments (NMEA talkers) to allow input via a single input port by one or more NMEA listeners. A typical example is the connection of a GPS and wind instrument to an auto pilot with a single NMEA input port. 

Multiplexers are often used for chart plotters or computers to feed in data from different  NMEA data sources. There are many excellent programs available that can process a variety of data produced by a number of marine instruments and that offer a tremendous amount of useful navigational information in a user-friendly format, which makes navigation easier and safer. Computer navigation programs today often allow input via multiple input ports (serial or USB), which at first glance eliminates the need for a multiplexer.  However, in most cases,  the only  way to connect a GPS and instruments is via USB ports.  This especially applies to laptops.  RS232-USB adapters can be used, but instruments output NMEA signals (RS422 standard) with different electrical characteristics. In practice the output of a GPS or marine instrument can often be directly connected to an RS232 port or to a RS232-USB adapter, but interfacing the equipment in this way can be a potential source of various problems. Also, the  wiring with multiple USB adapters is messy and often results in an unreliable system, not suitable for marine use.  

A setup with a multiplexer which is connected to the computer via a single USB connection is the preferred method and complies with the NMEA requirement for galvanic insulation of instruments.

Most chart plotters have a single NMEA input port and consequently  the only way to connect multiple NMEA instruments is via  a NMEA multiplexer.   

When the standard Brookhouse NMEA multiplexer was first introduced in 2002, almost 100% of the applications were for the basic NMEA combine function described above. While combining data remains a primary function, today our multiplexers are often purchased specifically for the extra tasks they can perform. A few examples:

  • Resolve NMEA compatibility problems. (Adapt NMEA sentences to make them compatible with newer or older versions so that older and newer instruments work together).

  • Filtering of data to remove conflicts or for optimization of performance of the navigation system.

  • Automatic data switching  for equipment backup.


Installation and Cabling

Installation is simple and can be carried out by anyone with a basic understanding of electrics. A clear diagram is included in the instructions and examples of integrated system wiring can be found under "diagrams" on this website. For connection of the instruments, follow the manufacturer's instructions.  For connection of  Raymarine Seatalk instruments, go to the Seatalk page.



  • 4 opto-isolated “Listener” (Input) ports for the connection of NMEA "talkers" (GPS, Windinstr. etc.) or RS232 (Computer).

  • 1 configurable RS232 input port for AIS receiver or computer return data, typically for Auto Pilot.

  • 1 Output RS232 port (typically for connection to computer)

  • 1 Output RS422 port (differential NMEA talker port)

  • Data speed:  4 Input ports: 4800BPS (standard NMEA speed)
    RS232 Output port: 4800/9600/19200/38400 bps selectable in setup mode, default 4800 bps.

  • Indicators: red LED for power, green LED for data-transmission.

  • Supply Voltage: DC 9-35 Volts.

  • Reversed polarity protection.

  • Power Consumption: 45 mAmps. @ 12V (with all ports active)

  • Physical size: 110x65x37mm (hxwxd)

  • Weight: 120 grams

  • Mounting: bulkhead mounting with screws.

  • NMEA  management and control:

    • NMEA Sentence Filtering

    • NMEA Sentence editing “on the fly”

    • Automatic port switching (mainly for GPS backup)

    • Data pacing for fast talking sensors and electronic compasses.

  • Options:

    • Raymarine Seatalk support

    • USB computer connection

    • User programmable LCD

Installation is straight forward. From each NMEA device 2 wires have to be connected (+ and - or A and B) to a NMEA IN port on the multiplexer. Also consult the user manual of the instruments to be connected.
Connection of the multiplexer to a computer is via RS232 or USB or both.
Connection of  an autopilot, a repeater instrument, Radar or any other NMEA listeners is via the multiplexer's  RS422 port (recommended NMEA) or the RS232 output. 



Prices, ordering and payment 





Note: Seatalk is a trade-mark of RayMarine.