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Old 04-10-2017, 08:13   #1
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Nmea 0183 RMC Sentence Problem (for use of VFkaps_pi)

PROBLEM: $IIRMC sentences recorded by OpenCPN VDR does not contain the time, variation or date fields. It is configured properly, has "A" and does have a checksum. This sentence is generated by my B&G ZeusT12 Chartplotter's GPS and converted to Nmea2000, Raymarine STNG, then Seatalk, then nmea0183. -Why? How do I fix this?

I have determined the following about the current B&G and Opencpn recording setup:

1. The VHF cannot be switched on because the GPS puck is sending a second GLL signal to the Autopilot Nmea0183 "IN" pin, which then gets sent out to the Raymarine ST bus and then is converted to Nmea2000 and is redundant and not very accurate. I need to disconnect the VHF gps puck now because we have two chart plotters now (Opencpn & B&G) and the autopilot should be getting this signal from B&G or OpenCPN.


2. ST60 Wind & Depth Instruments Raymarine Seatalk. These Seatalk signals are converted by the Raymarine STNG to ST Converter to Nmea2000 for the B&G Chartplotter. The two LED lights show normal.
The B&G Chartplotter displays Instrument data properly.
Instruments ---> SeaTalk ---> STNG Converter ---> Nmea2000 bus ---> B&G ChartPlotter

3. The B&G Chartplotter with GPS provides location information (RMC & GLL Sentences). The Raymarine Seatalk NG to Seatalk Converter and the Gadgetpoole "Tiny Link USB Seatalk to Nmea0183 Converter"Convert the RMC to nmea0183 for Opencpn.

B&G Chartplotter Gps ---> Nmea2000 ---> Raymarine STNG Converter ---> Tiny Link USB Seatalk to Nmea 0183 ---> Opencpn

4. OpenCPN requires Nmea0183. A Gadgetpoole "Tiny Link USB Seatalk to Nmea0183 Converter" sends data to Opencpn via USB. (Webshop) We have not configured Opencpn with a GPS in this instance so there is no GPS data going in the other direction.
Seatalk ---> Tiny Link USB Seatalk to Nmea 0183 Converter ---> Opencpn

5. The B&G $IIRMC signal does not contain the time, variation or date fields. It is configured properly, has "A" and does have a checksum. Why are these three fields missing? The reasons could be in the unit setup or in the two converters that I am using.
A. Raymarine STNG Converter (Seatalk & SeatalkNG bidirectional) Connected to the Nmea2000 bus on the B&G.
B. Gadgetpoole Tiny USB Link Seatalk to Nmea0183 Converter (bidirectional)
Output to USB in nmea0183 format
  • $IIRMC Speed over ground, Course over ground, Latitude, Longitude,
  • UTC time, Date
  • Optional an additional $IIGLL sentence can be sent for position information
Input

The SeaTalk NMEA Bridge reads and writes NMEA Data to/from the USB Port.
Processing of incoming NMEA data starts, when a complete NMEA sentence has been
received ( $xxxxx,.....<CR><LF>) from the boat computer. If checksum is valid the sentence is processed and translated to Seatalk.

  • $xxRMC Speed over Ground, Course over Ground, Latitude, Longitude, Time, Date
Same type of Data on NMEA & SeaTalk
Information available from like instruments on both Busses ( SeaTalk & NMEA ) are not converted.
If the information is not updated within 30 sec. on one bus, sending to the other bus is
activated again.

Attached is a small example of one of the files recorded.
Attached Files
File Type: doc whtest.doc (3.2 KB, 32 views)
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Old 09-10-2017, 18:27   #2
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Re: Nmea 0183 RMC Sentence Problem (for use of VFkaps_pi)

Just for curiosity I tested a BU-353-S4 Puck on a PC and both Time and Date are there. I've written B&G about the GPS to find out how I determine/see the sentences, but I believe the correct Date and Time on the unit is coming from GPS.

So that leads the culprit being some kind of conversion problem.

$GPRMC,002513.000,A,4221.1256,N,07104.5946,W,0.61, 354.77,101017,,,A*73
RMC - NMEA has its own version of essential gps pvt (position, velocity, time) data. It is called RMC, The Recommended Minimum, which will look similar to:
RMC Recommended Minimum sentence C
123519 Fix taken at 12:35:19 UTC <--- Has the time
A Status A=active or V=Void.
4807.038,N Latitude 48 deg 07.038' N
01131.000,E Longitude 11 deg 31.000' E
022.4 Speed over the ground in knots
084.4 Track angle in degrees True
230394 Date - 23rd of March 1994 <--- Has the date
003.1,W Magnetic Variation
*6A The checksum data, always begins with *
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Old 09-10-2017, 22:20   #3
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Re: Nmea 0183 RMC Sentence Problem (for use of VFkaps_pi)

Get an NGT-1 and install SK server to do the conversion to NMEA 0183 from N2K. If there’s a problem we can fix it, as you can log, debug and change every step of the conversion.

At the same time you gain the ability to convert most N2K data to XDR of your choice with a little bit of coding as well as logging all your raw N2K data.

Debugging black box conversions over several steps is like shooting in the dark around the corner.
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Old 10-10-2017, 16:51   #4
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Re: Nmea 0183 RMC Sentence Problem (for use of VFkaps_pi)

teppokurki ...
Quote:
Debugging black box conversions over several steps is like shooting in the dark around the corner. ...Get an NGT-1 and install SK server to do the conversion to NMEA 0183 from N2K
teppokurki you are likely right about this.. I probably should have purchased the NGT-1 to begin with (I used Artisense on another boat) but I got to this point in small steps. I am going to attach an Instrument diagram which might help I hope.

Also I think I'm going to try a couple of things to isolate the problem as best I can. If anyone has some other good ideas please let me know. Thanks.
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File Type: pdf NELL-Electronics-Diagram-B&G-RM.pdf (74.7 KB, 23 views)
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Old 10-10-2017, 19:31   #5
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Re: Nmea 0183 RMC Sentence Problem (for use of VFkaps_pi)

Happened on this. Using GPS data from a SeaTalkng/NMEA 2000 GPS source to supply a DSC VHF Radio - Printable Version

Using GPS data from a SeaTalkng/NMEA 2000 GPS data source to supply a DSC VHF Radio. To accomodate their VHFs, Raymarine introduced a feature within the v1.21 SeaTalk to SeaTalkng Converter software update permitting a SeaTalk to SeaTalkng Converter to transmit a limited set of 4800 BAUD NMEA 0183 GPS sentences

The SeaTalk to SeaTalkng Converter will output / transmit (tx) the following 4800 BAUD NMEA0183 v4.10 sentences:

- GGA - If L/L is present on STng, then GGA will Tx only populating data fields that are available, i.e. time/date etc.
- RMC - If L/L is present then RMC will Tx only populating data fields that are available, i.e. time/date etc.
- VTG - If SOG and/or COG valid in 129026 then VTG will Tx only populating data fields that are available, i.e. variation etc.

Its a software upgrade, however, most of my instruments are SeaTalk 1 so I need to maintain that compatibility, but this is hopeful information.
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