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  1. #21
    Join Date
    Sep 2005
    Posts
    2,455

    Default Re: NMEA in - Can 2 devices supply one input

    Quote Originally Posted by Spyro View Post
    No need to worry, If your DSC radio is not getting any NMEA input it will soon tell you.
    Dont know why you think it would do that? Mine currently has none (don’t ask) and doesn’t complain in any way. Just shows ‘———‘ for lat, long and time.

  2. #22
    Join Date
    Nov 2016
    Location
    Lincoln
    Posts
    302

    Default Re: NMEA in - Can 2 devices supply one input

    My last three, 2 Icom and SH all had alarms when GPS was lost after a short delay and this would have to be acknowledged

  3. #23
    Join Date
    Apr 2009
    Posts
    3,628

    Default Re: NMEA in - Can 2 devices supply one input

    Quote Originally Posted by BelleSerene View Post
    Dont know why you think it would do that? Mine currently has none (don’t ask) and doesn’t complain in any way. Just shows ‘———‘ for lat, long and time.
    My SH starts off like that, but then it gets very loud and insistent.

  4. #24
    Join Date
    Nov 2013
    Posts
    1,052

    Default Re: NMEA in - Can 2 devices supply one input

    Quote Originally Posted by BelleSerene View Post
    Dont know why you think it would do that? Mine currently has none (don’t ask) and doesn’t complain in any way. Just shows ‘———‘ for lat, long and time.
    Is that not because you don't have a position ever. So doesn't actually expect one. Once it has a position and it stops being updated most will alarm.

    If you then hit the red button it WILL still send. It will include the last pos and time u to 4hrs old. It will include your MMSI

    Returning to the OP, I'm inclined to ask what the risk of failure is... and what the risk of a switch failure is... are you adding more points of failure rather than redundancy?

  5. #25
    Join Date
    Apr 2017
    Location
    Denmark
    Posts
    184

    Default Re: NMEA in - Can 2 devices supply one input

    Just wire your gps signal leads from the GPS to the most reliable of your plotters as a Source . Keep it simple and avoid potential problematic bottlenecks.
    How often has your plotter lost it’s gps signal?. Maybe Occasionally during startup but if yours has a habit of stopping while you sail,then use your time instead to look into that problem , maybe relocate the antenna away from potential interference or just get yourself another reliable model.
    I understand your fears /arguments to wire 2 plotters up as a backup but that is just overkill , there are a million other more likely scenarios that can go wrong at sea.
    Ocqueteau 8.15,200hpNanni.
    Buster Sun R,25 hp outboard

  6. #26
    Join Date
    Apr 2017
    Location
    Denmark
    Posts
    184

    Default Re: NMEA in - Can 2 devices supply one input

    Quote Originally Posted by BelleSerene View Post
    Dont know why you think it would do that? Mine currently has none (don’t ask) and doesn’t complain in any way. Just shows ‘———‘ for lat, long and time.
    You may have inadvertently deactivated the alarm in the settings menu. Every DSC radio I have come across to date ALL have alarms to let you know that the DSC can not be used. I think it’s a legal requirement .
    Ocqueteau 8.15,200hpNanni.
    Buster Sun R,25 hp outboard

  7. #27
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    4,340

    Default Re: NMEA in - Can 2 devices supply one input

    Quote Originally Posted by prv View Post
    No, they each have their own built-in GPS receiver.

    Pete

    You might need to shout Pete, that information seems to have gone unnoticed.

  8. #28
    Join Date
    Jun 2014
    Location
    Gloucestershire
    Posts
    69

    Default Re: NMEA in - Can 2 devices supply one input

    Thanks to every one for thoughts, opinions and suggestions. Plenty for me to think about

  9. #29
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    4,340

    Default Re: NMEA in - Can 2 devices supply one input

    [QUOTE=Yeoman_24;6273517]Thanks to every one for thoughts, opinions and suggestions. Plenty for me to think about[/QUOTE]

    If you discount talk of NMEA 0183 networks and external "antennas" you have little to think about.

    You cannot connect them both together, whether or not they are both switched on at the same time.

    You have no NMEA networks, so no way to follow those suggestions.

    You have no external" antennas" (unless they were prehistoric they would be receivers anyway). Both of you plotters have internal GPS receivers. If they were both external it wouldn't really help, as they would be connected by plugs and it would be technically more difficult to connect both plotters and the VHF than it currently is.

    So, how to fix it. A single pole changeover switch is simple and will work, because you have Garmin plotters.

    Another option has been mentioned, fitting a pair of diodes. This doesn't address the data collision issues if you have both plotters turned on. It addresses a problem that doesn't exist. No damage would occur if they were both connected, it just won't work.

    A double pole switch will also work, but you don't need the second pole for the data lines, as Garmin rely on the -ve. What would be better use of a double pole switch would be to have the second pole switch the plotters -ve. This means that you cannot accidentally have the wrong combination of plotter/switch selection.

  10. #30
    Join Date
    May 2001
    Posts
    18,619

    Default Re: NMEA in - Can 2 devices supply one input

    If we can allow a bit of thread drift - it would of course be an ideal application for a PIC. It could listen to both transmitters and only fail over to the 2nd if there is no signal on the first. You might even be able to do it with an op amp and a handful of components.

    But if it is part of a safety-critical system then I would not seriously suggest that - at least not without having a manual switch as well.

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