NMEA check - how?

J

jason -and the arguenauts

Well-Known Member
Joined
15 Jul 2009
Messages
1,043
Location
south wales
Visit site
my set up involves the Raymarine Seatalk / NMEA interface box generating a certain NMEA sentence for the Simrad pilot to use. The pilot doesnt see the sentence but the Seatalk connection looks OK.

Is there a way ov viewing directly which NMEA sentences are actually appearing on a pair of wires? Hooked up to a lappy maybe.
 
Yes, you need a terminal emulator application running on the PC. Windows Hyperterminal is one, shipped with XP but not with Vista. There are freeware versions if you look.
Since my laptop is old, it has a serial port for connection. I don't know if you can connect via USB. Someone will come along and say if you can.
 
Yes there is. The simplest method I use is to use Hyperterminal available in Windows. This is in Start->All Programs->Accessories->Communications.

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.

Start up Hyperterminal & click on File->Properties.

In the Connection box, select the COM port you are using. This is normally COM1 for the serial port on your PC. If you only have USB holes, then you need a USB to serial converter & things get a little more complex since the machine will often install the converter on a different COM port when you plug it in.

Once you've set up the COM port, click the Configure button: bits per second = 4800, Data bits = 8, Parity = None, Stop bits = 1, Flow Control = doesn't matter but set None.

Close the dialog & click on the Call->Call menu. Now the PC shoudl receive the NMEA sentences.

If you want to fiddle with the config, you have to click the menu Call->Disconnect before you can change any settings.
 
jason -and the arguenauts said:
my set up involves the Raymarine Seatalk / NMEA interface box generating a certain NMEA sentence for the Simrad pilot to use. The pilot doesnt see the sentence but the Seatalk connection looks OK.

Is there a way ov viewing directly which NMEA sentences are actually appearing on a pair of wires? Hooked up to a lappy maybe.
Click to expand...

Strange I have the same problem with the interface feeding an ICOM VHF. Can anyone tell me which pins on the serial plug are wired into the NMEA + and - ta :confused:
 
Thanks everyone. Cable now made up - I'd forgotten I'd done it once before to run a GPS 128 at home, so it way a case of cheking the connections against the above advice and trying to remember what I'd done.

Off to the boat in the morning to find my missing sentence. Does anyone know if you can "overface" a gadget by sending too many sentences?
 
petehb said:
Strange I have the same problem with the interface feeding an ICOM VHF. Can anyone tell me which pins on the serial plug are wired into the NMEA + and - ta :confused:
Click to expand...

I had a thoroughly frustrating experience trying to feed GPS data from a Garmin 45 into an Icom DSC radio. Garmin said it was Icom but they did try to help. Icom said it was Garmin and couldnt care a toss. Never really got to the bottom of it, but the Garmin worked with everything else, and the Icom worked with another GPS.
 
Hi jason,

as well as the usual bits about only 1 NMEA talker to 4 listeners, it is possible to have too many sentences on your NMEA network. Basically the sentences take their turn on the network and then send the data. From my testing it seems that limit seems to be about 12 sentences in any 1 block of NMEA data, before an input is received. None of this seems to be covered in the NMEA Specs. If you can't see your sentence then try disabling some of the unused sentences from your raymarine devices. I am not sure what raymarine kit you have, but i would start with only enabling RMC (GPS locations) and disabling everything else unless you compass is not connected directly to your course computer in which case you need to add HDT (heading) and maybe WPT if you want to steer to a waypoint. if you are trying to control your pilot from a raymarine plotter then you may need to enable APA/APB (autopilot), from the sentences that you now have enabled you can add only the ones that you need, any more wil cause the network to slow down.

it would be worth taking a list of the sentences with you, i was going to attach it here but i cant get the .zip below 100k

You can however download it here
 
I suspect I have just that problem. Checking with the lappy showed the sentences going out but the autohelm denied that they ever arrived. And there were loads of them - like 43! Unfortunately, the Raymarine seatalk /nmea converter that is needed to get the one necessary sentence doesnt allow any yes / no options.
 
Hi Jason,


the Seatalk/NMEA convertor will output whatever is on the seatalk network. what kit do you have? If you have a plotter you should be able to prevent the sentences that you don't require. there are a couple of filters availble from people like brookhouse which seem to be the only way around the problem. If you have recently purchased the Raymarine interface can i suggest you return it and get one of these with the seatalk bridge

http://brookhouseonline.com/nmeamux.htm

it should solve your problems, not cheap i am afraid but not that different to a Raymarine box. No connection etc although i used said boxes to solve problems for people in the past.

if you want to send me a section of the data that you captured i will see if there are any other options, PM me if you would like
 
I dont know that the multiplexer would be the answer. there are log, depth and wind instruments together with the C80 on the seatalk bus but the C80 doesnt output the NMEA sentence I need which is VWR. but the nmea/seat;lkl interface does this along with a load of others that I dont need.

I've got a screen shot of the sentences going through the system but I'm not sure that will help. how could we reduce the number since the interface converts everything on the seatalk bus into nmea and there is no control overt what goes round the seatalk bus.
 
Hi jason,

it seems like the sentences may be being repeated (there are a number of sentences with the same meaning but using different codes), can you put a list of the 3 letter code sentences that you are seeing on here?, if i can see what the converter is putting out we should be able to find a way of reducing what you have so that you only get what you want.
 
Quick thought, are you seeing MWV as a sentence?, this is the same as VWR, actually slightly better but a bit older. Most AP's that i know off can process this one, although it may need a change in the setup to look for MWV in place of VWR. What simrad autopilot are you using?
 
The ones that should be going out are as listed. The only reason I say should is that I havent checked every one against the scrolling list on the lappy, just enough of them to know that there is an awful lot. I guess I can reduce some because the C80 allows you to cut down the list of those it sends by NMEA and which just pass through the NMEA / seatalk converter. There are 18 of those.

The autohelm is a Robertson / Simrad AP3000X of 96 vintage. Incidentally, the Simrad radar does see the NMEA sentences it needs.

AAM
APB
APB
BWC
BWC
BWR
DBT
DBT
DPT
GGA
GGA
GLL
GLL
GSA
GSV
HDG
HDM
HDT
HSC
MTW
MTW
MWD
MWV
RMA
RMB
RMC
RSA
RSD
TTM
VHW
VHW
VLW
VLW
VPW
VTG
VTG
VWR
VWT
WPL
WPL
XTE
ZDA
ZDA
ZTG

Apologies for the length of the list. Copied from a spreadsheet - the only way I could reconcile all the data.
 
Hi Jason, I have compiled the sentences you have listed above into a bit of a spreadsheet in an attempt to work out what is happening and used the manafacturers datasheets, i have attached it as a pdf.

looking at the repeat of the sentences it looks like you may have 2 talkers on the NMEA Network. Are you using the NMEA output of the C80 in addition to the interface box? as both of these would be classed as talkers, or have you got a GPS straight into the NMEA network, this would then make thr GPS and the seatalk box a talker

Any further info you could provide on current setup should help us resolve your issue

For instance, where on the nmea network do the following connect?

VHF - Make/Model?
Radar - Make/Model? (or are you using the C80 for This)
Autopilot - Roberston 3000X
GPS - make/model are you using a raymarine setalk GPS or a NMEA raymarine, or another
Fluxgate - Make/Model
Sailing Instruments - Make/Model

anything else you have would be useful, i will then draw up some type of diagram and we can work from there, at the moment it appears to me that there may be a coupld of talkers on the network, did this used to work, if so what has been added

shaung View attachment 342
 
Last edited:
You must log in or register to reply here.

Other threads that may be of interest

Lightwave395
Wiring mess
Replies
18
Views
789
thinwater
thinwater

Share this page

Top