NMEA 0183 Wiring

[Enoch Powell]

Any NMEA experts around?
I'm trying to rig up my NMEA instruments to talk to each-other via a multiplexter.
I have:
AIS with a built in GPS (Talker)
Chart Plotter (Talker and Listener)
VHF (Talker and Listener)
Auto Pilot (Listener)
GPS Repeater (Listener)

My multiplexer has 4 Listener outputs and 4 Talker inputs
My Chart Plotter 2 ports:
Port 1 Tx Out
Port 1 Rx In
Port 2 Tx Out
Port 2 Rx In

Any suggestions on how I can hook it all up?

[Enoch Powell]

I've attached some diagrams

[wholybee]

I would connect the AIS directly to the Chartplotter on port 2. Set that port to 38.4kbps (38000). Then chartplotter port 1 and the other 3 devices go to the 4 ports on the multiplexor. All of those set to 4800.

NMEA 0183 is not hard as long as you understand a few things.
Don't get caught up in wire colors. Manufactures do not all follow the same standard. You want to connect TX+ to RX+, TX- to RX-. So look at all the specs to find the signal names, and make a connection chart based on those names. Starting with a question "What color wire does the green wire connect to?" is going to get you a wrong answer.

More often that it should happen, manufactures will label + and - wrong. So, connect it temporarily and be prepared to reverse it if a connection doesn't work.

AIS is 38400, everything else is usually 4800.

Garmin, darn it they did a BAD thing. Note that Garmin uses the 3 wires instead of 4. The NMEA standard demands 4 wires, conforming to the electrical characteristics of RS422. Garmin did this to make the device easy to connect to a computer (RS232) but at the cost of messing up connections to other NMEA devices. Most people would think "just connect all the (-) wires to ground" but that isn't how it works! Please read this article on connection RS232 and RS422 together. And hope that this isn't a case where a manufacture miss labeled a wire.

https://stratusengineering.com/rs232...tronics-power/

Most of your connections to the Multiplexor will be straight foreword and shouldn't give you any issues. But Garmin's stupid engineering choice might cause some aggravation connecting it to the AIS and the Multiplexor.

[ScottRhodes13]

I hate to call myself an expert, but here's my 2 cents worth:

Don't bother with the multiplexer.
Connect the AIS to one of the chart plotter ports, configured at high speed.
Connect the VHF to the other chart plotter port.
Connect the listeners to the output port on the chart plotter that's connected to the VHF.

[smac999]

Originally Posted by ScottRhodes13

I hate to call myself an expert, but here's my 2 cents worth:

Don't bother with the multiplexer.
Connect the AIS to one of the chart plotter ports, configured at high speed.
Connect the VHF to the other chart plotter port.
Connect the listeners to the output port on the chart plotter that's connected to the VHF.

Then you won’t get heading from the pilot. The pilot is also a talker.

[Dockhead]

Originally Posted by Enoch Powell

Any NMEA experts around?
I'm trying to rig up my NMEA instruments to talk to each-other via a multiplexter.
I have:
AIS with a built in GPS (Talker)
Chart Plotter (Talker and Listener)
VHF (Talker and Listener)
Auto Pilot (Listener)
GPS Repeater (Listener)

My multiplexer has 4 Listener outputs and 4 Talker inputs
My Chart Plotter 2 ports:
Port 1 Tx Out
Port 1 Rx In
Port 2 Tx Out
Port 2 Rx In

Any suggestions on how I can hook it all up?

You've got 3 talkers and 4 listeners. Your MUX has 4 each talker and listener. You've a couple more on the plotter. What's the question? Just plug everything into the MUX and connect a MUX talker port to your plotter listener port. You can connect several listeners to one talker so you won't be short a talker port.

Only nuance here is that the AIS will want high speed, and you will then want to connect the MUX to the plotter with a high speed connection. The other will want standard speed (4800 baud).

Pilots sometimes want high speed but you've got enough ports to do that if necessary.

Pilot may also be a listener if it takes nav sentences from the plotter. In that case connect the pilot listener to the plotter talker.

And Bob's your uncle. Have a beer.

[ScottRhodes13]

Originally Posted by smac999

Then you won’t get heading from the pilot. The pilot is also a talker.

He said his pilot was just a listener. Don't know how common that is, but the old Raymarine Sportpilot on my boat is just a listener, at least as far as I can determine from the documentation. If he wants to add a heading sensor, it could be connected to the MUX port on the AIS.

[Dockhead]

Originally Posted by ScottRhodes13

He said his pilot was just a listener. Don't know how common that is, but the old Raymarine Sportpilot on my boat is just a listener, at least as far as I can determine from the documentation. If he wants to add a heading sensor, it could be connected to the MUX port on the AIS.

He doesn't mention any compass in his devices. So very likely he has a fluxgate connected to the pilot, which then sends that data out. Unless he just doesn't need heading for anything. If you don't have radar, maybe you don't need it.

[Enoch Powell]

Originally Posted by smac999

Then you won’t get heading from the pilot. The pilot is also a talker.

I think the pilot is just a listener that recieves waypoints from the chart plotter, but I could be wrong. Its a Raymarine S1000+

[Enoch Powell]

What I'm struggling to understand is that with the units that talk and listen, such as the Plotter, when wiring it to the MUX do I have to connect it to both an input (to talk) and an output (to listen) on the MUX?

Also is the AIS a talker and a listener, or just a talker?

[wholybee]

Originally Posted by Enoch Powell

What I'm struggling to understand is that with the units that talk and listen, such as the Plotter, when wiring it to the MUX do I have to connect it to both an input (to talk) and an output (to listen) on the MUX?

Also is the AIS a talker and a listener, or just a talker?

Yes, the chart plotter would need to connect to both the input and output of the mux.

Usually, an AIS is just a talker. However, sometimes they can be a listener, for example to receive heading information and include that in the AIS broadcast. That would be totally optional, however.

[Enoch Powell]

[QUOTE=wholybee;3912342]Yes, the chart plotter would need to connect to both the input and output of the mux.

So in my case, if I was hooking up the plotter to the MUX on the bottom input / output:
The blue wire from the plotter (Tx Out) would go to NMEA Talker 1 and
The brown wire from the plotter (Rx IN) would go to NMEA Listener C
Is that right?

[wholybee]

A talker is a Transmitter(Tx) and a Listener is a Receiver(Rx).
You always connect a Tx/Out/Talker to an Rx/In/Listener. The drawing you posted of the Mux is a bit confusing the way it is drawn. But is does show a device which it labels "NEMA Talker 1" connected to "Opto In 1"
It also shows 4 listeners all connected to "ISO out 1"

But is is important to understand the link I posed about about RS232 vs RS422. The Garmin chart plotter is RS232. So it isn't a one to one connection.

Maybe it would be easier, if on the MUX you relabel "Opto In" as "Rx" and relabel "ISO Out" as "TX"

[Enoch Powell]

Thanks for the help everyone. Very much appriciated!