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  1. #11
    Join Date
    Aug 2011
    Location
    River Exe
    Posts
    10,914

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

    Quote Originally Posted by BelleSerene View Post
    It's a messy solution I'm afraid. Half the time the switch will be selecting the wrong chartplotter, and the GPS won't have lat/long or time, which is inconvenient and in the case of needing to do a DSC, downright dangerous.
    Sure is. The one reason for me getting a DSC radio with a GPS receiver was I did not have to worry about hitting the wee red button if ever I needed to.
    Cynical Scots engineer.

  2. #12
    Join Date
    Jan 2003
    Location
    Clyde
    Posts
    6,450

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

    Quote Originally Posted by Sandy View Post
    Sure is. The one reason for me getting a DSC radio with a GPS receiver was I did not have to worry about hitting the wee red button if ever I needed to.
    No need to worry, If your DSC radio is not getting any NMEA input it will soon tell you.

  3. #13
    Join Date
    Jan 2003
    Location
    Clyde
    Posts
    6,450

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

    Quote Originally Posted by Rogershaw View Post
    2 way toggle double pole double through change over.



    P1 /2 would connect to the radio and the T1/2 would connect to each of the 2 GPS devices.
    That's the idea but you don't even need a double pole. Single switched nmea feed and common earth would be fine.

  4. #14
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Durban East Coast Africa
    Posts
    5,598

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

    Quote Originally Posted by Spyro View Post
    That's the idea but you don't even need a double pole. Single switched nmea feed and common earth would be fine.
    In most cases yes but NMEA is realy RS 422 differential and not knowing the exact spec of the 2 output devices switching both wires is safer in my view and the cost difference is not much anyway.
    Life is too short not to have a sea view
    Distantshaws tinyurl.com/ybrn7prn

  5. #15
    Join Date
    May 2001
    Posts
    18,556

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

    Quote Originally Posted by Rogershaw View Post
    In most cases yes but NMEA is realy RS 422 differential and not knowing the exact spec of the 2 output devices switching both wires is safer in my view and the cost difference is not much anyway.
    Most if not all NMEA devices I have seen use a single wire to transmit / receive and a common signal ground.

  6. #16
    Join Date
    Mar 2005
    Location
    Hants/Lozère
    Posts
    3,476

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

    Quote Originally Posted by bedouin View Post
    Most if not all NMEA devices I have seen use a single wire to transmit / receive and a common signal ground.
    I'm just about to update a bit and my Airmar H2183 heading sensor, Vesper AIS XB8000 transponder, SH GX2000 radio and Raymarine SPX30 autopilot ALL have two-wire differential NMEA 0183 connections.

  7. #17
    Join Date
    May 2001
    Posts
    18,556

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

    Quote Originally Posted by Hoolie View Post
    I'm just about to update a bit and my Airmar H2183 heading sensor, Vesper AIS XB8000 transponder, SH GX2000 radio and Raymarine SPX30 autopilot ALL have two-wire differential NMEA 0183 connections.
    Okay - I'll rephrase that - almost all Garmin devices use a single wire

  8. #18
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Durban East Coast Africa
    Posts
    5,598

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

    Quote Originally Posted by bedouin View Post
    Okay - I'll rephrase that - almost all Garmin devices use a single wire
    That's because Garmin don't comply completely with NMEA 0183 at the electrical level and some of their messages also are specific to Garmin.

    All my old SIMRAD comply but I can make then single wire to connect to non complement like my RS232 to USB to connect into my computer running OpenCPN.
    Life is too short not to have a sea view
    Distantshaws tinyurl.com/ybrn7prn

  9. #19
    Join Date
    Aug 2003
    Location
    Colchester, Essex
    Posts
    4,486

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

    I have this aboard with a Garmin 152 backing up my GPSMAP 751. It only works if you remove the data/power plug from the back of the plotter/GPS
    Larry Botheras

    Colvic Victor 35 "Gladys"

  10. #20
    Join Date
    Nov 2009
    Location
    Southampton
    Posts
    33,020

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

    Quote Originally Posted by BelleSerene View Post
    where are the plotters getting their lat/long and time data from anyway? - presumably from a 4800 baud NMEA 0183 network
    No, they each have their own built-in GPS receiver.

    Pete

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