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NMEA  Multiplexer with Repeater Display

The Brookhouse NMEA Multiplexer/Repeater

On boats with  modern instrument systems, an NMEA Multiplexer is a neccessity if  data from different instruments has to be fed into a (laptop) computer system to make maximum use of the  NMEA data in navigation or (race-)tactical software. The NMEA multiplexer is the central point in the system where all data passes through. It is therefore the logical and ideal place for intercepting the NMEA data and making it visible on a display. Not only does this provide a means of checking if all instruments are sending the data they are supposed to send, at the same time the display satisfies the need for a versatile, multi-channel repeater instrument. If the computer fails, all data is still available to the navigator via the mux display. It therefore has a valuable back-up function.  

We have taken our popular Standard NMEA Multiplexer and have added a compact LCD display unit with data selection push-button that makes this possible.  The result is a  compact, low cost NMEA repeater instrument, ideal for installation at the navigation station. The NMEA multiplexer does its work in the same way as without display and will still work normally if the LCD unit is unplugged.

Data from the instruments connected to the four multiplexer ports (NMEA talkers) is extracted from the NMEA sentences passing through the mux and is displayed in a clear, user-friendly format. By repeatedly pressing the selection push button one can cycle through the more than 20 data displays that have been implemented. If the selection button is pressed in for 2 seconds, the current display becomes the default display when the unit is powered on next time. 

There are many reasons for having a repeater display at the chart table. Navigation  programs usually only extract the NMEA data that they require and if there is an interruption in the data coming in from GPS or other instruments, there is often no immediate way of knowing this. By making the incoming data visible, independent of the computer, the navigator has access to all instrument data and can check the operation of instruments. It is convenient, while working at the chart table, to have information at hand such as course over the ground,  relative wind direction, wind speed, compass heading , water depth etc. This data may not be available via the computer’s navigation program or it may be cumbersome to go through various options and menus to obtain this data. The information can now be  provided instantly by the repeater display.

The instrument updates the displayed data each time the selected data-item is encountered in the data-stream.

 The Brookhouse NMEA multiplexer/repeater can also be a useful tool as an NMEA tester for marine technicians and installers.

Seatalk

The optional Seatalk feature is available for all models Brookhouse NMEA Multiplexers . The "Seatalk bridge"  makes connection of Seatalk instruments (RayMarine) possible via Multiplexer channel 1. Seatalk data is converted to standard NMEA format. Channel 1 is user-configurable for Seatalk or NMEA.

For the Brookhouse Multiplexer with repeater display, this means that Seatalk data can now also be displayed. For RayMarine users, this model offers 5 functions in one:

1. NMEA Multiplexer.

2. NMEA Repeater Display  (Selected data)

3. Seatalk - NMEA converter (Seatalk bridge, selected data)

4. Seatalk - NMEA combiner

5. Seatalk Repeater Display (selected data).

For full details on the Seatalk option, please refer to the Seatalk page on this website.

Installation

Conventional repeater instruments are often too big for installation at the nav station. Large displays are useful outside, in the cockpit, but the navigator, working at the chart table, only needs a small but easy to read display. The LCD display of our repeater provides just that. The led-backlighting makes the information very well visible under all circumstances. Installation is easy and does not require a great deal of expertise.

An earlier version of the Brookhouse NMEA Multiplexer with Repeater display had the LCD in the multiplexer-enclosure. The disadvantage of this was that all instrument cables had to be fed through the bulkhead for connection to the mux. With this new model, the NMEA multiplexer with cable connections can be placed out of sight, behind the bulkhead, behind the instrument panel or in a cupboard, and only the small, attractive display unit itself is mounted in a visible position at the chart-table. The result is much tidier. A single cable connects the display unit with the multiplexer. A standard 15-pin D-type plug is used to plug the display unit cable into the multiplexer. This makes the installation very simple.   

The display unit and selector push-button

The display is a standard LCD backlit display with 2 lines of 16 characters each.  At the beginning of the first line 3-letter NMEA sentence-type the data is extracted from is displayed. This can be important information when checking the operation of the instruments and in fault-finding situations.  Also on the top line is a description of the data on the second line, except in case of a GPS position. In this case the latitude is on the top line and longitude on the bottom line.

If a data-item is selected for display, but after 10 seconds no NMEA sentence containing the data is received, **No Input** is displayed. This is also displayed if data has not been refreshed for 10 seconds.                     

The display select  push-button is also used for configuring the NMEA multiplexer. If the button is kept depressed at power-up time, the mux starts in configuration mode. Selection of the RS232 output baud-rate is now possible and Channel one can be configured for Seatalk mode, if required.

NMEA data displays

There are many NMEA sentences and in each sentence there are a number of data-items. Much of this information is not useful for direct display. Therefore, only those data-items that have significance for the navigator have been chosen for display on the repeater LCD. However, it is very easy to add extra displays and if you are interested  in this product and you would like to see certain NMEA data to be displayed in addition to what is presently supported, please e-mail us and we will seriously consider making the requested additions.  At present, the following NMEA data can be displayed:

NMEA sentence type         Data-item

GLL                                    Latitude/Longitude of Geographic Position.

GGA                                   Latitude/Longitude.

GGA                                   Time (UTC)

RMC                                   Ground Speed.

RMC                                   Ground Course

RMC                                   Magnetic Variation

VHW                                   Water Speed

VHW                                   Heading (True and Magnetic)

VWR                                   Relative Wind Direction

VWR                                   Wind Speed

DBT                                    Depth below Transducer in Metres

DBT                                    Depth below Transducer in Feet

HDT                                    True Heading

HDM                                    Magnetic Heading

HDG                                    Magnetic Heading

HDG                                    Magnetic Variation

HDG                                    Deviation

VLW                                    Total Distance Travelled

VLW                                    Distance Trip

MTW                                   Water Temperature

VTG                                    Track Made Good - Magnetic

TTM                                    Tracked Target Message (Radar) - detection only.

Note: The above is data that can be displayed on the LCD. Naturally, all NMEA data is passed from the connected instruments to the output port.                              

USB 

Many of today's laptop computers have no RS232 port and only support USB.  There is now a USB interface available for this model NMEA Multiplexer as a reasonably priced optional extra. The integral USB adapter allows direct connection of the NMEA Multiplexer to a computer USB port. Units, equiped with this USB 1.1 compliant adapter can still be connected via a serial RS232 port as well. A USB cable of 1.8m (6 ft) length is included as well as USB driver software for Windows 98, 2000, ME, Windows XP.

  Specifications:

• 4 Input ports for NMEA "talkers" (GPS, Windinstr. etc.) or RS232 (Computer).

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

• Data speed:  4 Input ports: 4800BPS (standard NMEA speed), RS232 Output port: jumper selectable 4800/9600 bps, 19,200 bps selectable in setup mode.

• LCD Display unit.  LCD: 2 lines of 16 characters. Size: 64x17.5 mm. Character Dot Matrix: 5x7.  Screen/Option selection pushbutton.

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

• Supply Voltage: DC 9-15 Volts.

• Power Consumption: 50 mAmps. @ 12V, LCD backlighting: 100mAmps.

• LCD backlighting on/off switchable with selection pushbutton.

• Physical dimensions mux enclosure: 110x65x37mm (hxwxd)

• Physical dimensions LCD enclosure: 67x87x32mm (hxwxd)

• Weight: 180 grams

• Mounting Multiplexer: bulkhead mounting with screws.

• Mounting Display unit: bulkhead mounting with screws.

• Filtering and "on the fly" editing.

• Automatic GPS backup switching.

• LCD is user programmable. 

• Options: Raymarine Seatalk support, USB.

Installation instructions of the standard Brookhouse NMEA Multiplexer apply. The display unit is simply plugged into the socket provided on the Multiplexer.   

Prices, ordering and payment 

More technical information        Brookhouse home 

 NMEA-start

Note: Seatalk is a trade-mark of RayMarine.