NMEA wiring: GPS to Autopilot & VHF

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homa

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I have a Garmin GPS, Raymarine S1G Autopilot and Standard Horizon DSC VHF.
(and Raymarine RL70 Radar/plotter)

I would like the GPS position sent to the Autopilot and VHF.
Am I correct in thinking that all I need to do is wire the GPS +ve and -ve NMEA "out" to the Autopilot "in" and then take the NMEA -ve and +ve from the autopilot "out" connection to the VHF -ve and +ve "in".

This way I only need 2 core between the instruments, or do I also need to wire the -ve and +ve "in" of the GPS to the Autopilot "out"?

Sorry for the long drawn out question, I'm sure someone must have a similar set up.

(I am planning to send the data from Autopilot to the radar/plotter via Seatalk)

The handbooks are not at all that helpfull as to whether I need to wire the 2 connections or all 4.

Thanks
Homa
 
[ QUOTE ]
or do I also need to wire the -ve and +ve "in" of the GPS to the Autopilot "out"?

[/ QUOTE ]No, you don't need to do this step. The scheme you suggest should work fine. Alternatively you could connect from the a/p's IN terminals to the DSC's IN terminals (that way both their inputs are in parallel and being driven by the GPS NMEA OUT. Another way (not so good) is to connect two (two core) cables to the GPS OUT and feed one pair to the a/p input and the other cable pair to the DSC.

The NMEA input to the GPS should remain unconnected unless you intend to send it routes or waypoints from a PC for instance.
 
Thanks danny,
I had wondered what the GPS INPUTS were for.

Can anyone explain why is it not advisable to have the GPS feeding more than one instrument ?

Cheers
Homa
 
I don't think the S1G will convert NMEA to Seatalk so that you can send Seatalk to your radar as you suggest, I think it only outputs the data that is supplied, but can you not send NMEA data to the radar as well. If you want to send Seatalk you will need Raymarines NMEA to Seatalk convertor at about £120.
 
NMEA output can feed upto about 3 instruments at once I recall. We have NMEA coming out of a Raymarine Chartplotter - it goes to a connector block and feeds VHF, SSB, and GPS repeater - just got the +ve and -ve 'input' wires from each item linked to the +ve and -ve 'output' wires from the Chartplotter.

Works fine - I recall others on here running 4 or 5 items from one NMEA source without a problem.

For us the chartplotter is also a radar, so we can use the NMEA input for heading data from the autopilot (auto pilot NMEA out into Chartplotter NKMEA input) this gives the radar accurate heading info from the autopilot's gyro compass.

If you start mixing Seatalk and NMEA you need the box Petehb talks about - easier to keep Raymarine stuff on Seatalk - ie use the Chartplotter and Autopilot on Seatalk and everything else via NMEA.

If you have a chartplotter why not run everything off this (autopilot via Seatalk and NMEA to the VHF) and keep the Garmin GPS seperate as a back-up? (I assume you have the chartplotter with its own GPS sensor?)

Hope this helps

Jonny
 
I still need water speed and heading for the radar which the Autopilot will send via Seatalk.

For position info on the chartplotter I suppose I could connect the GPS to both the Autopilot and the radar via NMEA, but no-one has yet explained why It's not advisable to connect more than one instrument to the GPS NMEA output.

Cheers
Homa
 
Hi Johnny,
Unfortunately the Radar/Plotter does NOT have its own GPS, hence I need a position input from the external GPS.

For the Radar/Plotter it looks like I need this NMEA-Seatalk converter then because I need the heading from the Autopilot Gyro, the speed from the log (both seatalk) and a position from the GPS (via NMEA).

Have I got that right or is there another way?!

Cheers
Homa
 
[ QUOTE ]

The NMEA input to the GPS should remain unconnected unless you intend to send it routes or waypoints from a PC for instance.

[/ QUOTE ]

You can also connect the GPS input to the VHF output. This should pass position reports and distress call positions as waypoints.

John
 
[ QUOTE ]
... no-one has yet explained why It's not advisable to connect more than one instrument to the GPS NMEA output.

[/ QUOTE ]

I connect 5 instruments to the output of my GPS without any problems.

John
 
ok, scenario 1:

The Speed will output Seatalk so no issue there.

If the Autohelm output's Seatalk your sorted in that department too.

Then you need to get the Garmin GPS NMEA output to the Chartplotter and VHF - easy as both will listen at the same time.

(Chartplotter accepts Seatalk and NMEA simultaneously - there are three connectors on the rear of the C series - one for Seatalk (talks and listens), one for Seatalk 2 (advance version of Seatalk but no use to you I wouldn't imagine) and one for NMEA - therefore you can have a Seatalk network for Raymarine stuff and a NMEA network for other stuff running at the same time).


However, Scenario 2:

If your autopilot won't output Seatalk you have a problem as you can only have one talker on NMEA (you can have many listeners as I indicated above, but only one thing talking - ie if you have GPS position going out via NMEA you can't also have heading from the autopilot going out too as only one will get through ... multiple listeners, single talker). If this is the case you need a NMEA multiplexer (£150 ish) or a NMEA / Seatalk converter.

Therefore you have Speed via Seatalk
VHF on NMEA output from Garmin
Chartplotter GPS on NMEA output from Garmin
Autohelm via NMEA / Seatalk converter or a NMEA multiplexer to chartplotter

Or, Scenario 3:

As scenario 2, but instead of using a multiplexer ....

A cheaper solution maybe to get a setalk GPS anteenea (Raystar 125 or 120) to make the chartplotter have its own GPS (on ebay for £100 ish) - this way you would get GPS via seatalk and put the autopilot data via NMEA (assuming Autopilot won't talk on seatalk). That way you would have

Speed via Seatalk
GPS via Seatalk
Autopilot on NMEA input to chartplotter
VHF on NMEA output from chartplotter
Garmin GPS stays disconnected from anything and is a good backup.

I think therefore the first thing to do is find out from Raymarine whether your Autopilot talks in Seatalk, if so its easy peasy, if not you need to consider either option 2 or 3 above. Personally I would go option 3 as cost is similar and you end up with a spare GPS as a back-up.

Jonny
 
Hi Jonny,
I have the older version RL70 Raymarine Radar/Chartplotter
It is not a C or E series.
My autopilot does output seatalk and NMEA but I understand that it will not convert NMEA to Seatalk.

Therefore for the radar/plotter how about, NMEA from the GPS for position, and Seatalk from autopilot providing the speed & heading info ?

Cheers
Homa
 
[ QUOTE ]
but no-one has yet explained why It's not advisable to connect more than one instrument to the GPS NMEA output.

[/ QUOTE ]You certainly can connect several 'listeners' to one 'talker'. I usually connect them in a 'daisy chain' rather than fanning out several cables from the talker. That's the setup I suggested as an alternative to yours in my first reply.
 
[ QUOTE ]
Therefore for the radar/plotter how about, NMEA from the GPS for position, and Seatalk from autopilot providing the speed & heading info?

[/ QUOTE ]

Sounds good to me. Your set-up would then look like this:

Autopilot - Seatalk Output to Chartplotter
Speed / Depth etc - Seatalk Output to Chartplotter
Garmin GPS - NMEA Output to Chartplotter
VHF - NMEA Output from Garmin GPS

This would work fine, as the Seatalk bus is running on all Raymarine kit quite happily and on NMEA you have 1 talker (Garmin GPS) and 2 listeners (Chartplotter and VHF - you could also link laptop etc if you wanted to).

I assume the RL70 has Seatalk and NMEA inputs (I would assume it does).

Just need to get wiring now! A word of warning, the Seatalk and NMEA cables tend to be very thin and delicate so care needs to be taken and the connectors fastened securely to avoid them being damaged if the cables get knocked etc.

Good luck

Jonny
 
Thanks Jonny,

The RL 70 has both Seatalk and NMEA (and HSB - I think that's what its called)

I've run most of the cabling (4 core) just wasn't sure whether to connect the 2 or 4 cores.
I now understand what you mean by don't mix the Seatalk and NMEA. - i.e. think of what they are sending rather than don't use both seatalk and NMEA.
I shall daisy chain the connectors, because that's how I ran the cabling. I'll try just the 2 out cores from the GPS to start.
Have also labelled all the cores.
I bought the "NMEA cable" from JGTec, any idea why the cable should have 2 black cores , one red and one white?
Cheers
Homa
 
Hi Petehb,

For the Radar & MARPA I need a fast heading sensor - this comes from the Autopilot rate gyro. I also require a water speed - this comes from the log.

I don't really need a GPS input, though it could be useful for own ship or target Lat/Long. It is strongly not recommended to have SMG or COG for MARPA

Cheers
Homa
 
[ QUOTE ]
any idea why the cable should have 2 black cores , one red and one white?

[/ QUOTE ]

It should be "twisted pair" cable; If there are 4 cores, they will be arranged as two pairs. Most likely one of the blacks is paired with each of the coloured cores. You would need to carefully strip some of the outer sheath off to tell which black went with which colour. (i.e the 'pair' would be twisted together within the cable itself.)

Andy
 
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