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nmea wiring help please

Old 08-26-2011, 10:22 AM
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J.D
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Default nmea wiring help please

Gentlemen, I’m having trouble connecting NMEA wiring between 3 devices and getting them to work together. I’ve received help from the wiring wizards on this forum before, so I’m sure some one can set me straight this time…. Thanks in advance.

Sending GPS data from: Humminbird 785c Chart Plotter.
Red to batt. +
Black to batt -
Data wires: black, white, red

Sending data from the Humminbird GPS to:
Furuno FCV echo sounder
Red to batt. +
Black to batt -
Data wires: yellow, green, black, white, blue, orange, brown.

Sending data from the Humminbird GPS to:
Raymarine Sportpilot Plus autopilot.
Brown to batt +
Blue to batt. –
Data wires: red, black, yellow, and “screen”?? ( I think they mean the shield around the wires ? )

My biggest confusion is how to connect the ground wires. I am not sure about connecting any of the data ground wires together, or to the negative side of the battery. I believe I understand the “data out / transmit “ and “data in / receive “ part of the equation.

I’m hoping some one would take the time to give me wire by wire connection help and a better understanding of the necessary ground connections.

Thank You very much
Jim S.
Old 08-26-2011, 01:11 PM
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NMEA is pretty straight forward. Any/all of the grounds can be connected together. The [data out] from the sender is connected to the [data in] of the receiver. No more than one talker on the circuit and try to keep the listeners at 3 or less.
Old 08-26-2011, 01:47 PM
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Your data out/transmit unit will the unit you want the information from, this should be your GPS. The data in/receive unit is the unit you wish that data to be received by, this should be the sounder and auto pilot.

The data wires should have both send and receive + and -. You can connect all the -'s together and ground them to the 12v electrical system, just FYI some NMEA units will not have a separate - for data as they use the ground from the power the source. Then you will need to connect the transmit + from the GPS to the receive + from the auto pilot and sounder.

I would use a small terminal block for the connections so you can change or update later.

Hope this helps.
Old 08-26-2011, 04:32 PM
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Once connected make sure the baud rate is set the same on all devices.
Old 08-26-2011, 05:58 PM
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NMEA connections are not as straightforward as some may think thanks to manufacturers not complying with the standards recommendations. Some talkers/listeners use differential signals as is recommended, and some use single-ended. If an output has two separate wires either labeled A and B, or + and -, then it is differential. If there is only an A or + and ground, then it is single ended. You should never connect a B or - output to ground. This will cause an extra load on the driver and can actually cause serious damage to it. If your going to connect a differential output to a single-ended input, you would use the A or + wire of the output to the A or + input of the listener and then connect ground from the talker to ground of the listener, leaving the B or - output of the talker disconnected. It's ok to connect ground from a single ended talker to the B or - input of a differential listener.

Hope this is not too confusing. The one thing you should not do is connect a B or - output to ground as has been suggested. It may work but it is a no-no and may eventually cause damage to the driver in the talker.

Eric
Old 08-27-2011, 07:09 AM
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J.D
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Thanks to all who posted... Everything is much clearer now and I'm sure I'll get things connected properly !!

Jim S.
Hilton, N.Y.
Lake Ontario
Old 08-29-2011, 07:30 AM
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On the HB units there are three wires; Red, White, and Black. Red is power (for what I don't know), White is NMEA + Out and Black is NMEA - Out. DONT USE THE RED WIRE.

After that it is easy. Match your polarity and cross your In's and Out's. "+ Out" on the HB to "+ In" on the AP and FF.

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