linking lots of different nmea gadgets

[wotayottie]

got simrad autohelm, anritsu radar, raymarine plotter and instruments and planning on an Easy AIS. Handheld Garnmin plugged into the 12 v and the "network" at the wheel plus an ICOM DSC radio. Have the Raymarine interface box to convert NMEA into / out of Seatalk. And it will be handy to have the But how do I connect them all?

Do I use the interface box as a sort of bus and connect all in parallel? or do I connect them all to a sort of ring main? How do things like the autohelm or the radio deal with two slightly different position sentences buzzing round the system, one from the Raymarine, one from the Garmin?

 

[Phoenix of Hamble]

you can only have one 'talker' on an NMEA network...

To have more than one 'talker', you need an NMEA multiplexor....

And to have more than 3 or 4 'listeners', you need an NMEA buffer...

Take a look at this

 

[nimbusgb]

You can link up to 3 NMEA listeners to 1 talker

You can't put the garmin talker and the raymarine talker on the same bus without using an intelligent mixer and if you get two seperate position sentences you will have trouble. To do this you'd need an intelligent mixer that prioritises the inputs from one port over another.

You didn't specifically mention a Raymarine GPS. Is that separate again?

Which RAY plotter? Instruments seatalk? I presume so since thats the box you mention.

Easy AIS will need NMEA input at 4800 baud and will output it onto the AIS output line at 38400 baud.

AIS will need to be set up on the RAy plotter precluding using serial in for NMEA 0183 ( 4800 baud ) at all on that port. So you will probably be best off using the seatalk output from a raymarine GPS.

Garmin handheld GPS's don't output true NMEA and will give you all sorts of level compatibility challenges especially running from helm to nav station. Rather plug into 12v at the helm and transfer nav info manually or straight from PC at nav station. ( i take it the h/held is so that you dont need to go downstairs to see the chart plotter )

Thats a start /forums/images/graemlins/smile.gif

Which autopilot? Do you need any data connectivity to the radar?

 

[BlueChip]

[ QUOTE ]
You can link up to 3 NMEA listeners to 1 talker

[/ QUOTE ]

I've got at least 6 listeners on my Garmin 128 and all work fine

Yeoman plotter
ST5000+ autohelm
Radar
ICS Navtex / NMEA repeater
ICOM DSC VHF
Raymarine NMEA/seatalk converter
and occasionaly a PC Plotter

 

[Phoenix of Hamble]

The standard defines a maximum of 3 I think. However, you can sometimes get away with more... It depends how tolerant the devices are of low signal levels....

The bigger problem for the OP is two 'talkers'. This is a no-no on an NMEA bus..... and can't be done without all sorts of weird results.... for that an NMEA mux will be required.

 

[starfire]

Apologies - off topic.

But, what did you use to produce the diagram ?

 

[wotayottie]

At the moment there is a raymarine gps feeding into the c80 plotter which in turn is joined via seatalk to the instruments. there is an early sinrad / robertson pilot with its own compass and helm sensor but which will steer by the wind when I give it the appropriate NMEA sentence from the raymarine interface device. there is an anritsu / simrad radar which is getting a position feed which can only be coming from the C80. I havent yet bought the AIS or connected up the garmin handheld. MES tell me that I cant get the C80 waypoints via nmea to the garmin so I will probably not bother connnecting that in at all.

 

[Aeolus_IV]

If you have multiple talkers and listeners that need to receive from either you can either install some manual switches to route the traffic statically from talker to listener or install a NMEA 0183 multiplexer which will do all the clever stuff for you. I bought one from these guys a few years ago ( Shipmodul ) which has worked without configuration or fuss ever since.

Have a care with the AIS stream, although it is "NMEA" in form, it invariably runs much faster than normal NMEA (38.4k bits/s instead of 4.8k bits/s IIRC). But this isn't normally an issue as this is normally only of interest for a chartplotter.

You may find that you get some interesting effects if you bi-directionally connect two networks. When I first set mine up I had the GPS sentences heading out of the GPS as NMEA through a bridge onto the Instruments network (not Raymarine), and then coming back as NMEA having been converted from GPxxx to IIxxx sentences. Didn't stop things working, but was a waste of limited bandwidth. A firmware upgrade on the bridge enabled some control over which data when in which directions through it.

I suppose that I am saying that it is worth getting a handle on what's actually going on between bits of kit as it'll help you make sure it does what you want. I found a laptop and an old serial terminal emulator program really excellent tools for doing this.

Regards,
Jeff.

 

[nimbusgb]

Drawings produced with SmartDraw a slightly more versatile competitor to Visio.

It has pdf export native and can also export into excel. From there you can export it to a jpg.

I have used it to produce a lot of documentation for our boat.

 

[nimbusgb]

Ok
The drawing will let the autopilot read the wind via the seatalk/ NMEA converter.

You will have to swap the raymarine GPS over to Seatalk output. ( the 125 does this with just wiring it differently )

If in future you fit a DSC radio that will need to be connected on the multidrop link so that AIS, A/P and DSC all receive from the seatalk/NMEA converter

 

[smartcom]

There's nothing in the NMEA spec on how many listeners can connect to a talker - 3 or 4 is normally safe, nd beyond that add 1 at a time till it all stops working.
You can also look at Actisense for NMEA multiplexers, NMEA/RS232 converters etc.
Also Sailtron in Holland - I've seen a nice auto chngeover switch from them - feed in 2xGPS units, if the primary one goes down it switches over to the secondary one.