NMEA Combiner / Multiplexers
Products and Features Overview

Introduction

NMEA 0183 multiplexers play a central role in integrated marine electronics systems. The term "NMEA Multiplexer" is widely used, but the device is also often referred to as " NMEA Combiner".

Its original core function is combining data from multiple NMEA 0183 sources (NMEA "talkers") to a single data-stream, but the functions available in Brookhouse multiplexers go beyond this.  Brookhouse NMEA multiplexers have the ability to perform a number of extra tasks, that have proved to be essential in creating reliable, well performing integrated navigation systems. 

Since the introduction in 2002, Brookhouse NMEA multiplexers  are widely used on sailing and motor boats as well as commercial vessels for connecting computers, chartplotters, instruments, radar, AIS etc. Brookhouse multiplexers offer high reliability and unique features at affordable prices.

One of the most important characteristics of a good multiplexer is its ability to maintain data-integrity, even under very high NMEA input load conditions. This is determined to a high degree by the efficiency of the multiplexer's buffering mechanism. The buffering system of Brookhouse multiplexers is second to none, which results in excellent performance. This is made possible by the use of the latest state of the art micro-processors and well-designed firmware.  To read what Brookhouse users say about the product, click here.

Installation of a Brookhouse multiplexer is straight forward, no in-depth knowledge of marine electronics is required. Most Brookhouse multiplexers are owner-installed. All connections are made via clearly marked external screw-terminals.

Our standard NMEA Combiner / Multiplexer combines NMEA 0183 data from up to four marine instruments ( NMEA-talkers ) into a single data-stream for input via a single computer port, or  “NMEA listener”. A configurable fifth input port is available for input from a computer or other RS232 or NMEA device. If set to 38400 bps, this port can be used for AIS, with limitations. A better solution for AIS is to use one of our special AIS multiplexers with baudrate conversion.

Several optional extras are available, such as Raymarine Seatalk-NMEA conversion and USB.   

With AIS (Automatic Identification System) receivers and transponders now widely used on both commercial and pleasure vessels, the ability to combine standard low speed NMEA talkers and high-speed AIS in one data-stream has become an important requirement.  Besides 38400 bps AIS support, the multiplexer is also required to process return data transmitted at 38400 bps from a computer or chart plotter, typically to feed a DSC radio with GPS lat/lon or an autopilot for steering to a waypoint or along a route.  For systems that include AIS, we recommend  one of the Brookhouse purpose-made AIS multiplexer models with baudrate conversion (models AIS and AIS-C).  

Brookhouse multiplexers offer many extra features, most of which are included in all models. During years of experience with setting up integrated computer/instrument systems, we have come across various  problem areas in NMEA connectivity. To tackle these problems, we have created effective solutions embedded in the multiplexer firmware, which can be activated by the user, as needed. This has made the Brookhouse multiplexer into an efficient NMEA traffic hub/controller, NMEA data and baudrate converter and switching device all at the same time.

We do not offer these extras in  expensive "advanced" models, they are available in all Brookhouse multiplexers. The advanced features are activated and configured during a simple setup procedure, whereby the options can be selected from a menu. Click here to see what it looks like. However, if only the basic multiplexer functions are required, no setup is necessary. Many of the Brookhouse multiplexer options are unique and are not available in other products. Here follows an introduction to some of the features:

Filtering and NMEA data manipulation 

Brookhouse multiplexers offer comprehensive filtering and data manipulation capabilities, even in the standard model. Filtering is very useful to alleviate the load placed on the navigation software or instruments by selectively removing redundant data. On the fly editing allows the user to program the multiplexer to make changes to NMEA sentences as they pass through the multiplexer. In integrated instrument/computer systems these tools, only found in Brookhouse multiplexers, are extremely useful for fine-tuning and will help to get the most out of instruments, computer and/or chart plotter. Not needed at the moment? You don't pay any extra for these features and it is good to know that if an NMEA compatibility problem is encountered one day, the multiplexer can offer a solution. Even complete NMEA sentence translations are possible. For example, you may install a new chart plotter that outputs NMEA 3.01 but your older autopilot needs NMEA 1.5 sentences. The multiplexer can be programmed in a simple way by the user to do the required sentence translation. You can also ask Brookhouse support if the required translation has been done before and if so, we'll be happy to give you the "script", which is loaded in your multiplexer following a few easy steps. Click here for more information.

Automatic GPS back-up switching  

Another important feature, also unique for Brookhouse multiplexers, is GPS back-up switching. This solves the problem of switching to a backup GPS if the main GPS fails. This is particularly important when sailing in waters with many navigation hazards. Interruption in the electronic navigation is avoided which makes this a valuable safety feature. We received the customer comment recently that this mechanism alone justifies installing a Brookhouse multiplexer. (Click here for more information)

A refinement of our GPS backup switching is now available. The original back-up switching mechanism looks at multiplexer input port activity. It is now also possible to look  for the presence of a specific NMEA sentence in a data stream and to switch to a backup source if the sentence is not found. The backup data can also be enabled selectively per NMEA sentence. This new feature is controlled by a small uploadable script, available from Brookhouse at no charge. 

The selective back-up switching is very useful for backup of a Seatalk GPS. If the optional Seatalk-NMEA conversion feature is installed, the mux can detect if the Seatalk GPS is active and enable another GPS source if not. It has also proved to be an extremely valuable feature for installations with AIS class B transponders. GPS data in the transponder output data stream can be suppressed by the multiplexer to avoid conflicts if the main GPS is working. If the main GPS stops, the multiplexer uses the transponder GPS as an automatic backup. 

For more information: click here

Baudrate conversion  

(Available in Brookhouse AIS/AISC  multiplexers)

For this feature please refer to "AIS multiplexers" on this overview page. For a detailed description: baudrate conversion options 

Automatic data stream switching  

(Available in Brookhouse AIS/AISC  multiplexers)

Especially, but not exclusively, on sailing boats, the following situation can occur:

The chart plotter or computer provides navigation data data to the auto pilot for steering to a waypoint or along a route. In addition a DSC radio or other NMEA listeners may be dependent on the chart plotter for NMEA input. This is fine as long as the chartplotter or computer is switched on, but this may not always be the case. On sailing boats the computer may be switched off to save battery power. If the auto pilot or other instrument is hard-wired to the chartplotter output via a single port, other essential data necessary for the performance of the auto pilot, such as speed and wind data, is not available when the computer or chartplotter is switched off.

The automatic data stream switching ability of Brookhouse multiplexers will connect one or more other NMEA sources to the autopilot input when it detects that the chartplotter or computer is not outputting any data. For example, the multiplexer may be may be programmed to connect the combined output of wind instruments and a GPS as alternative auto pilot or DSC radio input. This feature is activated from the multiplexer setup menu. More about this can be found under "baudrate conversion options".    

NMEA Data Pacing  

If an NMEA talker transmits data at a high frequency, this can have the effect that the receiver, e.g. a chart plotter or navigation software, has difficulty handling the large amount of data. This may result in  impaired performance or congestion, especially if there are also various other NMEA talkers outputting data at the same time. The Data Pacing option, which is available in all Brookhouse multiplexers, provides a solution to this problem.  (Click here for more information)

Optional extra: NMEA bridge for 
Raymarine Seatalk

A low-cost Seatalk interface option is available for all Brookhouse multiplexers, which allows connection of  the Raymarine Seatalk bus to one of the multiplexer input channels. Raymarine instrument data from all instruments, available on the ST-bus is translated by the multiplexer into standard NMEA sentences and output together with sentences from other NMEA sources. The mux "Seatalk port" is still configurable as NMEA port too. By combining the multiplexer function with the Seatalk to NMEA conversion, an efficient system is created which results in important cost savings.    (Click here for more information) 

Optional extra: USB

The USB option is very popular for connection to laptop computers without serial port and is sold with over 50% of our multiplexers. The USB port is in addition to the RS232 and RS422 ports, which are available on all  multiplexer models

Optional extra: A low-cost GPS PS2 mouse as primary or backup GPS

GPS mice can usually only be plugged in directly into a laptop or PDA. A low-cost PS2 (mini-Din) connector option now allows a PS2 GPS mouse to be plugged into the Brookhouse multiplexer as one of the NMEA talkers. Power is supplied by the multiplexer. Read more here.

Optional extra: Bluetooth connector

Most boat owners prefer reliable hard-wired connections for the transmission of critical navigation data.  However, there is some demand for bluetooth enabled multiplexers, mainly for transmission to a PDA or small notebook that can be used in different positions on the boat. Nevertheless, we have decided not to offer bluetooth as an integral feature of Brookhouse multiplexers for several reasons. In the first place, there are now a number of competetively priced serial-bt adapters on the market with very strong features, such as extended range. These units provide better functionality than any integral bt transmitter can do. Furthermore, it is advantageous to keep wireless transmission separated from the core tasks of the multiplexer for service reasons. Instead of integral bt, Brookhouse can offer an optional connector  for several industry standard plug-in type bt modules. 5V power is supplied by the multiplexer via one of the connector pins.  Please contact us for more information. 

There are several models Brookhouse NMEA Multiplexers available:

Standard NMEA 0183 multiplexer

Our standard, very affordable NMEA Multiplexer, loaded with useful features. It has four 4800 bps opto-isolated NMEA input ports, a fifth configurable input port plus  NMEA and RS232 output ports. Baud rates: 4800, 9600, 19200, 38400. Optional extras are RayMarine Seatalk to NMEA conversion (Seatalk bridge), integral USB interface for use with laptops without serial port. For full specification, click on the picture above.

AIS NMEA multiplexers

Models  NMUX-AIS and NMUX-AISC. The photo shows model NMUX-AISC. Both models combine standard NMEA talker data at 4800bps with high speed 38400 bps output from an AIS receiver or transponder. The combined data stream is transmitted at 38400bps to a computer and/or chart plotter. Consequently transmission of NMEA data in the opposite direction, such as data for the auto pilot or lat/lon input for a DSC radio, is also at 38400 bps. The reason is that in- and output baudrates of computer ports and chart plotters such as the Raymarine C- and E-series cannot be set independently; the baud rate is always the same for both directions. Therefore, if the computer or chartplotter's output is required to feed a standard NMEA listener such as an auto pilot, a DSC radio, a repeater instrument etc, the baudrate of 38400 has to be reduced to 4800.

The baudrate conversion function of the multiplexer is independent from its combine-function, with its own input and output port. The only difference between models AIS and AISC is that model AIS has an extra RS422 port for output to the Raymarine C- or E-series. The USB and Seatalk options are available for both models. 

For full specs and detailded description, click on the following links for more data:

Multiplexer model AIS
Multiplexer model AISC

The iMux - Wifi enabled NMEA 0183 multiplexer for iPad

The Apple iPad with iNavx application offers powerful marine navigation capabilities, using Navionics charts, at a fraction of the cost of a chart plotter. Features include AIS target plotting and full marine instrument support. However, the only way NMEA 0183 data from AIS, external GPS and instruments can be input by the iPad is via WiFi (wireless LAN). To unlock the full potential of the iPad for navigation, Brookhouse now offers the iMux, the NMEA 0183 multiplexer with Wifi output.

Two iMux models are available:

1. The standard NMEA 0183 iMux

2. The iMux-ST for Raymarine Seatalk installations.

For further details, click on the following link:

Brookhouse iMux

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