The Brookhouse NMEA multiplexer with display is now user-programmable

In an integrated computer/instrument system, the NMEA Multiplexer is the traffic junction where all NMEA data traffic merges and passes through. It is therefore also the ideal point to place a “window” to make the instrument NMEA data visible. The LCD display option for the Brookhouse multiplexer provides this window and can be an invaluable tool for the navigator, with better functionality at the nav-station than a repeater-instrument, which is designed for use in the cockpit. The display has been available as an option for some time, but we have now made it fully user-programmable so that it can be adapted for specific purposes. It is possible to display combined data extracted from different NMEA sentences on the same user-defined screen and the user can add his own favorite descriptive text. The sequence in which the screens are showed when the selection button is pushed is also determined by the user, as well as the default power-on screen. 25 different screens can be defined to display 50 different user-selected NMEA data-items in any combination or sequence. Navigators love it!

We have listed some uses for the compact display:

• As a repeater instrument at the chart-table that only takes little space, but is still very readable with the clear backlit 32-character alphanumeric display.
• To complement NMEA data-displays on the computer-screen. It is often not possible or less desirable to display instrument data on the computer screen, as the screen is dedicated to navigation or simply because the software does not support the required displays or combination of displays the navigator is interested in. The mux LCD displays the required data separately, independent from the computer.
• As a backup source for all navigational data if the computer fails and the navigator has to revert to manual navigation.
• As a diagnostic tool to check the proper functioning of instruments.
• Low cost smart GPS units (GPS mice) which only output NMEA data are becoming increasingly popular for use with computers. However, if the computer fails, the GPS data is not available for “manual” navigation. The Brookhouse mux LCD can be programmed to display all essential GPS data.
• To display data from non-standard (proprietry) NMEA sentences.
• As a compact data display in the owner’s cabin. A number of users have installed the LCD to be able to check time, water-depth, wind direction and speed from the comfort of their bunks, while anchored.

A few examples of useful data-combinations for the navigator, working at the nav-station:

• SOG (Speed over ground, from GPS) and Speed Through Water (from log) displayed     together will give, at one glance, a good indication of the effect of current.

• COG (Course Over Ground, from GPS)  and Heading (T) from fluxgate compass displayed together show the effect of current and drift to adjust the course to steer by the helmsman. 

• Relative wind-angle and Heading displayed together make it easy to determine the wind-direction.

•  XTE (Cross-Track Error), distance and bearing to waypoint for determining a course to steer.

• Depth and water temperature.

 Many other combinations are thinkable and will often depend on the individual preference and methods of the navigator. A convenient, consecutive group of navigation screens may be defined for navigation if the computer is switched off and a second group to complement the computer when it is on. If engine data is available in NMEA sentences, screens can be defined for RPM, oil pressure, temperature, battery charge current etc.

 Programming the screens

Let the word “programming” not scare you off! It is a very simple process and as long as you know what you want to display, where you want it on the 32-character screen and what the text or symbol is you want to place before or behind it, you will find it easy and fun to do. It only needs to be done once, but you may want to make some changes later, until you have the combinations and sequences that work best for you. We provide the definitions of the standard screens, that are already programmed when you receive the multiplexer, on CD. You may find these useful as they are or perhaps you wish to change the sequence or format or make additions. Making changes to the existing definitions is very easy.

The screens are defined in a text file, which can be edited with any text editor such as standard Windows program Notepad. Before you begin, it is a good idea to print out the NMEA sentences generated by your instruments. There are many ways to “capture” the NMEA sentences in your computer. A common way is to use standard Windows program Hyperterminal. Your instrument documentation will explain the contents of the sentences and if not, information is available from many sources on the Internet. A screen definition for the Brookhouse multiplexer consists of text and data items that will be extracted from NMEA sentences. You need to specify which sentence, from which port (optional), which parameter (count comma’s), and where on the display you want the data placed. Detailed instructions are provided. You may find it helpful to use pencil and paper to draw the lay-out of data and text on the LCD the way you want it. After you have created or edited the text file with definitions, all you need to do is upload it to the multiplexer to store it in the flash memory. The multiplexer has to be connected to the computer via the RS232 port or USB. No special software is required for the upload. Standard Windows program Hyperterminal or any other terminal program will do the job. You start the terminal program while the multiplexer is switched off. You press the ESC key on the computer’s keyboard, keep it depressed and switch the mux on. This tells the mux that you want “set-up mode”. A message sent by the mux will appear in the  Hyperterminal window with instructions on how to proceed. If errors in the definitions are detected, the upload stops and the mux reports the error. After correction, the process can be repeated until the definitions are accepted. Now switch the multiplexer off and back on again and your self-defined screens can be displayed on the mux LCD one by one by pressing the pushbutton. 

Features summary

• A maximum of 50 NMEA data-fields can be defined to be displayed in maximum 25 different screens.
• Any NMEA data-field or part thereof, present in an NMEA sentence that passes through the multiplexer, can be displayed on any required position on the 32 char. LCD screen.
• Any fixed text or symbols can be displayed to describe the data, units, etc.
• If the multiplexer has the Seatalk feature installed, data from the Seatalk instruments can be displayed as well, as the multiplexer looks for data to be displayed after the Seatalk-NMEA translation has taken place.
• Optionally, only data received from a certain multiplexer port number and with a certain NMEA ID (e.g. $II or $GP) can be selected for display. This is useful in case there are multiple sources of the same data.
• NMEA data-fields may be split in separate sub-fields for better readability. Example: Latitude 3710.375,S as present in the NMEA sentence can be displayed as 37º 10.37’ S
• Multiple data-fields from the same NMEA sentence and/or from different NMEA sources can be displayed on the same screen.