GPS speedometer wiring to older GPS

DracoDan

Seaman Apprentice
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Feb 22, 2012
Messages
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I recently picked up a Teleflex/Veethree GPS speedometer for my new (to me) 1999 Formula 330 SS. I had planned to hook it to my very dated but functional Magellan NAV 6510 charplotter (I intend to upgrade this later) since the manual says that it supports NMEA 0183 2.0 output. On closer inspection, it looks like the GPS takes in differential input, but outputs what is called "Single ended". In other words, the only output wire is the positive, and the manual says to connect the negetive signal wire of the downstream device (my speedometer in this case) to ground.

Can anyone tell me if my speedometer will work with this type of signalling (instead of differential)? If not, is there a way to just hook up the speedometer to the GPS antenna in parallel?

Thanks
 

DracoDan

Seaman Apprentice
Joined
Feb 22, 2012
Messages
44
Re: GPS speedometer wiring to older GPS

Nevermind, I found the answer myself here - http://www.navcen.uscg.gov/pdf/gmdss/taskForce/NMEA_7.pdf

Each NMEA 0183 interface circuit shall have only one talker, and a maximum of 3 listeners. Where more than 3 listeners for a single talker is required, a signal expander shall be provided that amplifies the talker output to drive a greater number of listeners.

Older single ended devices may operate as a talker with a single differential listener by connecting the single ended talker signal to listener?s ?A? connection and connecting the listener?s ?B? connection to ground. Where more than one listener is desired, a signal expander that converts the single ended signal into a differential signal is recommended.

So it looks like I can go either way. Does anyone know if there would be an advantage to one or the other? At this point I think I'll be connecting the speedometer in parallel to the GPS receiver (the talker) so later on I can pull out the charplotter without affecting the speedometer. I'm thinking about replacing the charplotter with a Panasonic Toughpad when they get around to releasing it, that will have its own GPS receiver.
 
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