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      Hi all I was wondering if anyone had an insight into my problem…

      I have just got back from the boatshow and after a couple of long chats with Raymarine and Garmin I now have a bit of a dilema.

      My Garmin charplotter and Radar need a fast heading compass to stabilise the radar overlay and allow MARPA to be utilised. (£600!)
      My Smartpilot X10 has a fast gyro compass that can deliver the required information.

      The Garmin outputs NMEA to the Smartpilot for routing etc.
      The Smartpilot CAN output NMEA to the chartplotter for fast heading updates – BUT is not wired up to send the data.

      When I have quizzed the installer of my system why this was not wired up, I am being told that the circular references cause a feedback loop and renders the system unoperable. (Something about being told to do something whilst it is already doing something else and no halt message?)
      Is this a clash between manufacturers or as NMEA is a standard comms is there a way around it?



        I think I can see what your installer is worried about. If each NMEA sender transmits its own information and also repeats back anything it receives you will quickly overload the system. However, it is normally possible to restrict what a sender sends out, particularly to filter out messages it has just received, to avoid the problem.

        Check out the manual for the SmartPilot. You will probably find you can restrict it to just send out the required heading info. If so, connect up the NMEA output to the Garmin input and see what happens. If you have any problems and have a laptop PC handy, you can use a serial input to tap into the NMEA bus to monitor the NMEA sentences that are being transmitted.



          Well, I have had the smartpilot connected and yep – there is a feedback loop.

          The only way that I have found it to manifest itself (so far) is that when you cancel a course on the plotter it takes about 25 seconds for it to break the communication with the smartpilot.
          If when you set a track on the plotter and activate it – then tell the pilot to follow the track, all is well.
          Stopping the navigation in the plotter does not immediatly cut off the communication with the pilot though.

          I am being told that a multiplexer will get around this.



            ** Radar overaly is now MUCH better and Marpa works fine though!

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