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Wiring for DSC/GPS

Old 05-24-2005, 02:24 PM
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Default Wiring for DSC/GPS

I have a Lowrance LMS 337df and a Navman 7100 VHF. The dealer hooked up the NMEA as follows: yellow to yellow, and green to silver(ground). According to the manual(s) that should be right, but the lat/lon doesn't show up on the VHF, (says "no gps info"). I have a MMSI and it is entered in, all settings on both devices are right, unless I'm missing something, so anyone have any ideas before I trailer it back 50 miles to the dealer( who admitted he wasn't all that familiar with the whole DSC thing). Thanks.
Old 05-24-2005, 03:44 PM
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Default Re: Wiring for DSC/GPS

Here is an old schpeil if Thom's. It may or may not help, and may be more info than you're looking for, but shoot through it and see.......


To do the best I can to answer your questions here goes.

Think of them as talkers and listeners, that helps.

Here are the rules:

Positive lines connect to positive lines.
Negative lines connect to negative lines.
Every NMEA Circuit requires both a positive and negative line
No listener can be connected to more than one talker.
A talker may be connected to more than one listener
It will not hurt anything if you hook up any NMEA connection wrong.

That's all the rules there are. The number of listeners that can be supported by a talker is limited by the voltage of the talking line. If you get too many none of them will work, there will not be intermitent operation, it will be pass/fail. Just for your own thinking go ahead and figure that a talker can give data to up to 4 devices before it fails. Shorter and heavier wires can stretch this number but only so far.

OK, lets look at your question in more detail.

GPS will always be a talker, sometimes a listener
VHF will always be a listener, maybe a talker
Fuel Computer will always be a listener, rarely a talker
Fish Finder can be both a talker and a listener.

The GPS can talk to everyone, so let it.

Run all of your negatives to a common buss, so that way you won't even have to think about them again. Then run your output data + wire from the GPS to a terminal strip and then connect the VHF input, the Fuel Computer input, and the fish finder input to it.
The next taker in line will be your fish finder. Take its output + and tie it to the GPS input +. The only thing that leaves is conditioned on your VHF being NMEA output capable and your chartplotter having the latest version of the software in it. If those conditons are met then connect the VHF output+ to the second channel data input+ on the GPS and you will be able to display the position of polled DSC radios that are active in your area.

I think that got them all, leave a space or two open on the interconnect strip (buy a couple of those small interconnect strips with the jumpers by Blue Seas) for the addition of an auto pilot and radar somewhere down the line.


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