Newbie NMEA0183 help, please

[SkyeMarine]

Hello,

New to the forum. My husband and I just purchased a used boat with some rather dated electronics onboard. We'd like to do refit but that's not in the budget this year. So I'm trying to get the existing instrumentation to work together a bit better.

We have:
Raymarine GPX400 chartplotter
ICOM IC-M604 VHF
Robertson AP300X autopilot

and we'd like to get them communicating with each other via NMEA0183, as they don't all have NMEA2000 ports. Everything was hooked up when we bought it but none of the instruments indicate that they are connected, e.g. the VHF displays "No Position".

I'm playing around with an Arduino with an RS422 level converter:


This is connected to a cable from the "NMEA 0183" port #2 from the chartplotter. I wanted to initially confirm that it's outputting NMEA at 4800 baud, as the setup screen from the unit indicates.

Some basic code:


It seems to be transmitting something about every half second or so, which seems right, but all I'm getting is a bunch of gibberish on the serial monitor. I expected some ASCII characters.


We're very new at NMEA and I haven't played around with Arduino very much yet. If anyone could provide us with some friendly suggestions, it would be greatly appreciated!!

Thank you,
Erin and Jon
SV Erin Skye

[SkyeMarine]

Hello,

New to the forum. My husband and I recently purchased a 2001 catamaran with some rather dated electronics. We'd eventually like to do a complete refit but that's not in the budget for this year, so we're trying to get the existing electronics to work a bit better together.

We have:
Raymarine GPX400 chartplotter
ICOM IC-M604 VHF
Robertson AP-300X autopilot

The goal is to get them communicating via NMEA0183, as they don't all have NMEA2000 capabilities. Things were connected previously but it doesn't seem to be working, e.g. the radio displays "No Position".

In trying to debug what's going on, I'm first trying to understand what the chartplotter may be putting out on its NMEA0183 port. I have the transmit pair from that port going to an RS422 level converter and into an Arduino Uno:



Here's some simple code I found on the web:



The configuration screen of the chartplotter shows that it's outputting NMEA0183 on this port at 4800. I expected to see some ASCII characters but am just getting a bunch of gibberish.



Obviously we are NMEA newbies so any suggestions on what to try next would be greatly appreciated!

Jon and Erin
SV Erin Skye

[Dsanduril]

Not super familiar with the Arduino, but I believe your Serial.begin also needs to be at 4800.

 void setup()  
 {  
  Serial.begin(4800);  
  nmeaSerial.begin(4800);  
 }

[Be Free]

The "Serial" entry should be for the USB connecting the RPI to the console software on the PC. If you are getting the message "NMEA initialized..." then you have the console speed correctly. Try commenting out everything in the loop to test the console connection.



The "NMEASerial" should be talking to the RS422 device. It looks like a speed mismatch on one side of the RS422 or the other. The documentation for the level converter should tell you what speed(s) it can use and what the default is if you've not set it.



NMEA0183 on the other side of the converter can be 4800 (default) or 38400 (high speed). The level converter is working at the physical layer and is just passing electricity.



It's been a long time since I've worked with serial communication protocols, but that output looks like a speed, word length, or parity mismatch to me. It should be 8N1 - 8 bits, no parity, 1 stop bit (IIRC).


Good luck.

[Be Free]

Muddy thinking on my part. The level converter has no speed settings. Don't go down that rabbit hole. Speed has to match the device on the other side of the converter.

[Lake-Effect]

You might initially skip the Arduino, get yourself a basic USB to serial board (eg FTDI board ~$5), connect your RS422 adaptor to that, and then use any old PC serial terminal program to view the data stream.

You might need to connect the ground from the chartplotter to the RS422 board. An oscilloscope would be useful for diagnosing the connections and the level conversion.

[Pete7]

Can you confirm the model of the chart plotter? It its an older Raymarine unit it is probably transmitting Seatalk.



Pete

[SkyeMarine]

Thanks, everyone, for your replies so far. Let me see if we can get our hands on an oscilloscope and see what's actually coming out the wires...

Erin

[SkyeMarine]

Sorry for the duplicate post. I posted this one, tried to edit the picture links, and then it completely disappeared. I've since posted a 2nd version, so this one can be merged or deleted.

To answer Pete's question, this box seems to have both types of ports:



I'm trying to read the output of either of the NMEA0183 ports.

Erin

[muttnik]

Originally Posted by SkyeMarine

The goal is to get them communicating via NMEA0183, as they don't all have NMEA2000 capabilities. Things were connected previously but it doesn't seem to be working, e.g. the radio displays "No Position".

I agree with Lake-Effect that the arduino is an unnecessary complication although I understand that the complicated tool you have is often better than the cheap and easy one you don't.

The plotter and VHF you have there aren't that old: less than a decade and high end stuff. I don't think I'd be in rush to replace them.

You don't mention a GPS in the mix. If you mean it's a GPM 400 (which from the diagram you posted I think it is) I'm not sure that that has an integrated GPS, which would account for "No Position" on the VHF. Obvious question: Is you position correctly displayed on the plotter screen?

[ranger58sb]

Originally Posted by muttnik

You don't mention a GPS in the mix. If you mean it's a GPM 400 (which from the diagram you posted I think it is) I'm not sure that that has an integrated GPS, which would account for "No Position" on the VHF. Obvious question: Is you position correctly displayed on the plotter screen?

The IC-M604 can be configured with it's own GPS antenna; ours (previous boat) came with the GPS antenna plug-in in the box, so I thought it was maybe a standard option. You could use another external source (we eventually did), but that ICOM antenna plug-in would easily solve the position display on the VHF.

And then that could be output to a plotter or whatever via the radio's 0183 OUT.

If that helps. Or is relevant.

-Chris

[muttnik]

Originally Posted by ranger42c

The IC-M604 can be configured with it's own GPS antenna; ours (previous boat) came with the GPS antenna plug-in in the box, so I thought it was maybe a standard option. You could use another external source (we eventually did), but that ICOM antenna plug-in would easily solve the position display on the VHF.

And then that could be output to a plotter or whatever via the radio's 0183 OUT.

Interesting. By "Antenna" do you mean a simple antenna connecting to an internal GPS or a small external gps unit which feeds the radio NMEA-0183 sentences? I have the earlier M603: the only way to get dynamic position in to that is via the NMEA input and the only sentences the manual says it outputs are DSC and DSE (ie it doesn't repeat input GPS although full disclosure, I haven't confirmed that in practice), so the configuration you're suggesting wouldn't work with mine. I see how a radio with integrated GPS which outputs that GPS would work as you say but I wasn't aware the M604 was substantially different from the 603 in that respect (though if your experience says otherwise I'm happy to take that).

[Portage_bay]

Originally Posted by SkyeMarine

I'm trying to read the output of either of the NMEA0183 ports.

Erin

Here's what I'd try. It's been a very long time since I've set up NMEA 0183 so I may have left some things out....

Get something like Lake Effect mentions in post #6. Download OpenCPN and Go to Options (the gear icon) / Connections / Add Connection. Configure a serial port to Serial, Input, 4800, Data port will be dependent upon your computer. Tick the "Show NMEA Debug Window" You should now see what's coming into the computer.

Sometimes when hard wiring it DIY like you are you can get the (+) / (-) data wires reversed which will display gibberish.

If you have trouble determining the data port, it can be as clear as mud, download a trail copy of Rose Point Coastal Explorer. That software can auto search for active NMEA data ports. But you must have your wiring and baud rates correct for Coastal Explorer to find the data.

[Lake-Effect]

Here's one source for the FTDI USB-to-serial boards I mentioned. Very useful if you like to mess with serial interfaces.

And there are also complete encapsulated USB-to-serial interfaces with built-in adapters for RS232 or RS422 serial.

[SkyeMarine]

Originally Posted by muttnik

You don't mention a GPS in the mix. If you mean it's a GPM 400 (which from the diagram you posted I think it is) I'm not sure that that has an integrated GPS, which would account for "No Position" on the VHF. Obvious question: Is you position correctly displayed on the plotter screen?

Thank you -- this was an "ah-hah" moment for us. We had assumed that the plotter *was* the GPS, but now we realize that it's a consumer of the GPS location information, hence it's NMEA 0183 out port doesn't contain the location. Some re-wiring is in order and we'll see if that successfully delivers the time & location information to the VHF.