NMEA check - how?

[jason -and the arguenauts]

The C80 is inputting all its available NMEA sentences into the interface as well as the Seatalk. The NMEA coming out of the interface goes to the VHF, the radar and the autpilot all connected in parallel. The compass is connected direct to the autohelm which then outputs a heading NMEA signal which is received direct by the C80.

It would be easy enough just to disconnect the C80 NMEA output.

I reckon the next step is to couple up the lappy to the autopilot NMEA input to make sure there isnt a break in the wire - so far I've only checked at the interface. The autopilot NMEA input is at the far end of a cockpit locker. Then the step afterwards is to run off every C80 NMEA output just to see if reduced number of sentences makes a difference.

Trouble is, there isnt really one NMEA 0183, there seems to be different interpretations by different kit makers and they arent always compatible.

Appreciate your efforts to try and help .

 

[ShaunG]

Hi jason,

That effectivley makes 3 talkers, the interface Box, the C80 and the Autopilot course Computer.

It would be worth removing the C80 Output completely. The C80 will send all of it's data over seatalk to the interface box. This should reduce talkers to 2.

So, everything raymarine uses seatalk only except the interface box which outputs all seatalk data as NMEA. According to the manual for your AP there is a NMEA in and NMEA Out (which Multiplexes). Take the NMEA out from the Seatalk Interface to your Radio, Radar and AP ( or you could take the NMEA Out from the seatalk interface direct to the NMEA in of the AP, then NMEA out of the AP to radio and radar). Take the NMEA Out from you AP to the NMEA in on the setalk interface. This would effectivly make 1 talker as the SeaTalk interface can muliplex the AP NMEA with the seatalk data.

you should choose whichever setup suits your exisiting wiring the best. In your case it would be worth checking cable continuity and would be very worthwhile plugging the laptop directly to the wires at the AP.

If it has been working in the past i suspect that due to the multiple sentences on the network you will not have had the best performance. NMEA will work with mulitple talkers but you can have an issue of data conflicts which will cause poor response

How does the above meet with what you already have?

 

[jason -and the arguenauts]

Its easy enough to do what you suggest except changing the autohelm NMEA output to go to the interface rather than the C80. But I can disconnect that completely anyway.

I'll have a go and let you know what happens.

 

[ShaunG]

good luck jason, the return path from the AP is not essential, although i guess it may be feeding heading data to the radar and back to the seatalk network. If everything works the way i have suggested but without the heading data you would need to add the AP NMEA out link in

ShaunG

 

[Ubergeekian]

First, you need to connect the NMEA to the PC. You'll have to make up a cable with a 9-pin D-type connector available from Maplins. Pin 5 is ground, pin 2 is receive data. Connect pin 2 to the NMEA out+. It may not have the + in the name. Connect the other wire to pin 5.

I have a vague memory that NMEA is a current loop like RS422 rather than a voltage-based system like RS232. Most serial ports couldn't care less, but some USB-Serial converters may be more sensitive.

 

[jason -and the arguenauts]

I think it's voltage not current but certainly the normal patch lead and the prolific software work fine with the above wiring.

 

[jason -and the arguenauts]

Well, we did try! I cut off the NMEA feed from the C80 and checked the NMEA feed wire to the autohelm but it still didnt see any data input. Just an occasional flash which suggests something is getting through but the timing of the sentences isnt suitable.

Cant see anything else to do - can you?

 

[exfinnsailor]

Which NEMA

Hi Jason

Had a quick look at the Simrad Auto Pilot and it uses NMEA 2000 which is totally different to the other NMEA 0183 . NMEA 2000 is a multi talk multi listen protocol and runs at a considerably faster speed . So you should check which one you have .

Normal NMEA 0183 is 4800 speed and you should be able to see sentences on a laptop as described . All talk units will do just that and do not wait for a spot to say something . So you can get giberish on the lines if you have more than one talker . Thats why they use NMEA 2000 .

We have a Beneteau 323 and the chart plotter receives data only . It has a Raymarine auto pilot that has a seperate control head which excepts data from compass , gps , and outputs data to the chart plotter and auto pilot so the chart plotter just displays info and nothing else .

The Raymarine unit can be set to send seatalk or NMEA 0183 sentences.

I have found Raymarine Technical very helpful in the past . You may be trying to find the answer to a question they already know.

 

[ShaunG]

Hi Jason,

Can you have a look at the attached diagram and see if it shows the setup you should now have?

The diagram shows the best way to link all this together, if you were only receiving broken messages at the AP end it would be worth ensuring that all other NMEA devices are disconnected (VHF and Radar) and monitoring again. it could be that some of your other Kit is stealing the messages and causing a voltage drop, this should not happen but very few manafacturers actually use opto-isolaters in their NMEA Input/ouput as per NMEA Specifications. If i have missed anything off the diagram or listed the incorrect kit then let me know as it may have an impact.

View attachment 378

 

[hightech]

Which simrad pilot. The installed ones have a built in reader that can show the data on screen.

 

[Bevdent]

All this is very well if your laptop has a 9 pin port. Mine has a 16 pin port only. I have tried a 9 to 16 converter but it dosen't work. Any ideas?

 

[ShaunG]

do you have USB, if so a serial to USB connector will work.

You can wire straight to a d25 connection (the larger one) but the connections are different, the site below details the connections (2,3,7) in place of 2,3,5 and 2,3 on a DC25 are the opposite to a DB-9 (9 pin)

http://www.beyondlogic.org/serial/serial.htm#2

 

[ccscott49]

Do you perchance know if the icom fluxgate for the compass, outputs NMEA?

 

[ShaunG]

Icom Fluxgate? i can't find a reference to a Icom fluxgate, do you have a part number that i can look up?

i am checking a raymarine this weekend, if you do need a NMEA compass then NASA make one as well as Autonnic http://www.autonnic.com/802570900035631E/products/D02395C4263D85C5802570B70047EAE2 who appear to be the OEM for tacktick looking at the internal part numbers.

if you could get a part number for the ICOM i could probably help

regards

ShaunG

 

[ShaunG]

sorry, just noticed that it was you with relation to the raymarine, sorry about posting the autonnic details again. I will take a look at my raymarine this weekend

 

[jason -and the arguenauts]

Hi Jason,

Can you have a look at the attached diagram and see if it shows the setup you should now have?

The diagram shows the best way to link all this together, if you were only receiving broken messages at the AP end it would be worth ensuring that all other NMEA devices are disconnected (VHF and Radar) and monitoring again. it could be that some of your other Kit is stealing the messages and causing a voltage drop, this should not happen but very few manafacturers actually use opto-isolaters in their NMEA Input/ouput as per NMEA Specifications. If i have missed anything off the diagram or listed the incorrect kit then let me know as it may have an impact.

View attachment 378

Shaun

The diagram is correct except the blue line from the AP which goes direct to the C80