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nmea 0183 to RS232

41K views 26 replies 10 participants last post by  Bill-Rangatira 
#1 · (Edited)
Hello,

I am interested in sending some nmea 0183 data to my computer. I believe that all I need to do is connect the correct nmea wires to the correct pins on a DB9 connector and then plug it into the serial port of my PC.

Is that correct?

Specifically, I want to connect a Standard Horizon GX2100 AIS VHF unit to my PC so that Seaclear can display the AIS data. The GX2100 manual states that the brown wire is NMEA HS (AIS) data and the green wire is NMEA common (ground). So all I need to do is connect the brown to DB9 pin 2 (received data) and the green to DB9 pin 5 (signal ground). The AIS data is at 38400 baud.

Is that correct or am I missing something?

Thanks,
Barry
 
#2 ·
Damn, that's an old computer...most new ones don't have an RS-232 port on them. :) It sounds like you've got the right pin outs..since the NMEA Data out + should connect to the RS-232 RX Data pin (2 in a DB9 connector).

Don't forget to set the parity and stop bits properly. It should be 38400, 8 N 1. IIRC. :)

Hello,

I am interested in sending some nmea 0183 data to my computer. I believe that all I need to do is connect the correct nmea wires to the correct pins on a DB9 connector and then plug it into the serial port of my PC.

Is that correct?

Specifically, I want to connect a Standard Horizon GX2100 AIS VHF unit to my PC so that Seaclear can display the AIS data. The GX2100 manual states that the brown wire is NMEA HS (AIS) data and the green wire is NMEA common (ground). So all I need to do is connect the brown to DB9 pin 2 9 (received data) and the green to DB9 pin 5 (signal ground). The AIS data is at 38400 baud.

Is that correct or am I missing something?

Thanks,
Barry
 
#3 ·
NMEA to PC

That's right, though there are a few things to watch for. Chances are it will work fine first off. If not, here are some things I've encountered:

The NMEA standard actually calls for balanced (neither side grounded) signals. You can usually connect NMEA - to PC ground, but there are exceptions.

A Raymarine ST60 Multi, for example, sources steady voltage on NMEA+ and switches the NMEA- output. I use a multi at the nav station as a convenient source of NMEA, and found that it worked if the PC (with a USB-serial dongle) was connected to only the ST60, but when I also plugged in the USB cable from my Actisense mux, it died. Reason was that the mux grounded the PC to the boat's negative, effectively sorting out the Multi's NMEA.

I also ran into an Eagle GPS which had some "protection" circuitry in its serial output cable, consisting of a diode and series resistor. This did not provide enough signal to drive another device, in his case a VHF radio's DSC input.
The circuit would have made more sense on the input, rather than output, but I didn't design it. Maybe it was a manufacturing error.

(If anyone wonders why I'd use the Multi's output when I have an Actisense mux, it's because the latter is used to combine VHF DSC out with the Autopilot's 10 Hz Fast Heading output for the E120 Multifunction Display. The combined output is nearly flooded by HDG sentences. I also use th Multi's output to send wind speed/direction to a serial terminal server which is on my WiFi, so I can check on conditions when I'm away from the boat, when the Chartplotter and Mux are off but the Wind instrument and Multi stay on. They're on now, even as the boat is on its cradle, and I can check wind with NavMonPC or PolarCom.

A lot of words to qualify which it will "probably" work. Good luck.
 
#4 ·
NMEA 0183 is RS422 which is different to RS232, actually if everything is working within their respective specs then the RS422 will not provide the voltage levels for the RS232. Luckily modern RS232 chips work beyond the spec and can cope with the RS422 signals. I have never yet found an RS232 connection not to work with an RS422 input but it is not guaranteed.
You can get isolating RS232 to RS422 cables with a DB9 connector already fitted. This will also give you protection against any potential ground loop problems.

It should be noted that you shouldn't use the B/- wire if your device has one. This is not compatible with the RS232 connection, just use the ground (pin 5) and the A/+/Data (pin 2) wires.
 
#5 · (Edited)
ST60 Multi NMEA -vs- RS232

I agree almost 100% , ActiSense, but would like to clarify that my comment applied specifically to the NMEA output of the Raymarine ST60 Multi.

The Multi has a 12V current-limited source on NMEA+, spec'd at 11.2 V (on 12V in) at 80 mA, and actually drives its NMEA- output via an optoisolator to ground.
The test procedure calls for a 1k resistor between NMEA+ and NMEA- and looking for data pulses on the NMEA- line. I haven't tried, but logically (pun intended) that would produce inverted RS-232 (which would be closer to MIL-188, if I recall correctly).

In the case of this particular Instrument, using NMEA+ and Ground would produce a steady "spacing" condition on RS-232. Given the >5v swing, using NMEA+ and NMEA- always worked ok for me with an *ungrounded* laptop, and of course is fine via a MUX with a "real" NMEA input, which is the better way to go. I did not have the internal instrument schematic when I first did the hookup.
 
#6 ·
Good point, isolated outputs will sync to whatever they are driving so are totally safe. It is rare though, many manufacturers don't even bother with isolated inputs as required by the latest NMEA 0183 spec. So finding any with isolated outputs (that are not required by the spec) is to be applauded. Life would be so much simpler if everything was isolated as standard, too much to hope for in this cost cutting world though.
 
#7 ·
NMEA 183 to computer

Hi - My first post . I am really interested in the possibilities of NMEA 183 to computer and remote monitor connections. I read this post and decided to join in. This is going to be fun.
---------
I bought an older bass boat with some trick electronics on it. However, the problem is most is obsolete so I'm trying to "upgrade" it somewhat. It has a Lowrance Globalmap 2000 which will display both GPS/maps and sonar either individually or on a split screen. The map is okay for 1995 but I really wanted a modern hydrographic contour map which shows GPS position. So - I also have a new Dell mini with GPS so I ordered the Maptech topo map and that should take care of the mapping. Also have a small remote flat screen out of a car which I can remote to the laptop so the laptop mapping feature will be fine with a nice remote screen also. The boat has a Eagle sonar with a NMEA 183 output. I would like to take the Eagle sonar display and remote it to another flatscreen. Is this possible and if so how do I go about doing that please. cd
 
#8 ·
Hi - My first post . I am really interested in the possibilities of NMEA 183 to computer and remote monitor connections. I read this post and decided to join in. This is going to be fun.
---------
I bought an older bass boat with some trick electronics on it. However, the problem is most is obsolete so I'm trying to "upgrade" it somewhat. It has a Lowrance Globalmap 2000 which will display both GPS/maps and sonar either individually or on a split screen. The map is okay for 1995 but I really wanted a modern hydrographic contour map which shows GPS position. So - I also have a new Dell mini with GPS so I ordered the Maptech topo map and that should take care of the mapping. Also have a small remote flat screen out of a car which I can remote to the laptop so the laptop mapping feature will be fine with a nice remote screen also. The boat has a Eagle sonar with a NMEA 183 output. I would like to take the Eagle sonar display and remote it to another flatscreen. Is this possible and if so how do I go about doing that please. cd
NO.
 
#9 ·
This whole discussion appears to be relevant to a problem I am having. No intent to hijack....
I've got a functional Furuno GP 31 (GPS) trying to communicate with a new B&G h3000 instrument system via 0183. The B&G just ignores the Furuno, which has operated successfully with the B&G's predessor, an h1000. I have very limited diagnostic resources...no computer at hand at the moment.
The data stream from the Furuno seems to exist, that is, there is a series of positive-going (from 0) pulses, 2V at 1-1.5 seconds which, according to the B&G techs, is good news in that the pulses exist at all, bad news that the pulses are only 2V. I took the measurements at the input plug of the h3000. Furuno NMEA + out goes to the B&G + in; FURUNO out - to the B&G - in , not to gnd .

The Furuno folks are taking the position that even if the problem is not theirs, they are probably in the best position to do something about it. What a pleasant surprise THAT is.

Any comments?

Howard Keiper
Berkeley
 
#10 ·
Howard-

Remember that NMEA 0183 was originally specified as RS422, which is a balanced signal protocol, so the voltage levels are going to be relatively low. What version of NMEA 0183 does the Furuno use and have you updated the firmware in it? Most GPS units have upgradeable firmware and often, that can solve an incompatibility problem between it and newer hardware. Given that the Furuno worked with the H1000, I would say that the issue is likely an NMEA 0183 version incompatibility problem rather than a hardware one.
 
#11 ·
Thanks, SD, I'm rapidly coming to that conclusion too. It appears that both units are functioning as they should...just don't play well together.
I will see what's involved with upgrading the firmware...not holding my breath, though...the GP-31 is a discontinued product.
hk
 
#12 ·
You might luck out...they may have a newer firmware available for it that you just haven't updated to yet. :D

Good luck.
 
#14 ·
Part of the problem here is the confusion over NMEA and RS232, 422, or whatever.
When you send NMEA data to a device, those data come FROM the NMEA output, +, or -, to a NMEA input, + or -. NMEA is NMEA, NOT RS anything. Serial communications protocol specs...baud rate, stop bits, etc. have no meaning whatsoever.
Yes, you can convert, but you can't just plug an NMEA output into an RS input or vise-versa no matter how you jiggle the wires.
Howard Keiper
Berkeley
 
#15 ·
NMEA is NMEA, NOT RS anything
Quoting from the NMEA 0183 version 2.20 standard:
"The drive circuit used to provide the signal 'A' and the return 'B' shall meet, at a minimum, the requirements of EIA-422-A (December 1978)". So in fact NMEA 0183 (from version 2 onwards) follows the RS-422 standard specifically.
The confusion comes because version 1 was based on RS-232 but with a wider voltage range. RS-232 uses ground as the return path while RS-422 uses a dedicated return path typically labelled 'B'.
This makes connection of devices following the different versions more difficult. It is further complicated with some devices having the required opto-isolated inputs and others not.
Another problem is most manufacturers don't bother informing the user which version they are following and even cherry pick the cheapest option from each version. Just because it is brand new does NOT mean it follows the latest version of the standard.

Yes, you can convert, but you can't just plug an NMEA output into an RS input or vise-versa no matter how you jiggle the wires.
I do this almost every day without the need to jiggle anything, I just plug them straight in. Remember that a 'B' of a talker should NOT be connected to the ground of a listener.
Modern RS232 chips work beyond the spec and can cope with RS422 signals. I have never yet found an RS232 connection not to work with an RS422 (NMEA 0183) input but it is not guaranteed. Also, due to the change of spec between version 1 and version 2 the latter versions are required to cope with voltages above the RS422 so they can handle direct (un-converted) RS-232 inputs as well. The only thing to watch out for is ground loops.
The information in NMEA 0183 is basically just text so if you are only interested in the data then it doesn't matter which RS standard you follow to get the text from one place to another (for instance Airmar smart transducers use RS-485 to transmit NMEA 0183 sentences).
If you are not sure about you connections ask in the forum and someone will OK it for you.

-Howard
With both devices using A and B signals that is not your problem, both are following later than version 1, for the voltage levels at least.
going (from 0) pulses, 2V ..... I took the measurements at the input plug of the h3000
It sounds like you took the measurement across the A and B not across ground and A, can you confirm this? How did you measure the voltage? Using a meter on an active signal line is not always accurate.
When you had the h1000 connected was that using A and B for inputs or was it A and ground? Connecting a driving B signal into ground could have worn out the driver circuit of the Furuno. You may be able to rescue the situation using an isolating buffer box that can handle the low 2v input signal boosting it for the H3000 to read.
 
#16 ·
Wow, I stand corrected...many times over. I wish you'd been around last week. Yours is the most authorative info I've gotten on the subject since I got into my situation...that includes advice from Furuno and B&G.
Anyway, the fellow from B&G was being very helpful or trying to be, sensing (correctly) that I was not getting anywhere and told me with equal vigor that I was barking up the wrong tree...that the h3000 expected data from the GPS to be delivered to the NMEA IN jack. There are only two wires, and that the + out from the GPS should go to the + IN terminal. Well, OK, but it doesn't work. That's when the discussion got around to what a dope I was and maybe I got the NEMA jack and RS232 Jacks confused. I concluded that he was at least partially right.
I didn't mean to sound like I had the last word, and I apologize for that.

Howard Keiper
Berkeley
 
#17 ·
No worries Howard, you just sounded frustrated, didn't sound like it needed an apology at all but thanks all the same.

Our NMEA 0183 information sheet, containing everything we are allowed to give away regarding NMEA 0183, has been linked to by eherlihy in this thread (I can't link to it because of my commercial interests).
The thing with having to pay for standards is most people don't buy them so don't know what's in them.

I hope you have got everything sorted out now.
 
#18 ·
As it worked out, B&G had a big presence at the Strictly Sail Show, here in Oakland, and their senior tech, one Matt Fries, was there too. The owner of the boat in question and Matt discussed the situation and both Matt and another tech visited the boat. It turns out that they felt there was enough reason to replace the CPU. The exchange should be complete by the time I finish this.
Talk about customer service...wow.
Howard Keiper
Berkeley
 
#19 ·
I was interested in the comments "redline" made regarding the nature of the ST60 Multi's NMEA out signal. I also observed a +12 on the NMEA+ with a small drop every 2 sec when data is being output. If I connect the NMEA+ and NMEA- directly to a serial to usb adapter no rs232 data is present (this discussion thread explains why). I ultimately want to use the ST60 Multi as a low cost seatalk to NMEA repeater for the instrument messages it does output. I want to connect to an RS232 serial to usb device (IOGear GUC232A) and read the NMEA messages with software I am developing.

I was wondering if there was a simple circuit that would convert the ST60 Multi output to an RS232 signal which could be read by the serial/usb device. Of course I can go get a Raymarine E85001 or a special opto-isolator cable (cost almost as much as the E85001) or even a nice Brookhouse NMEA Multiplexer, but for now I was looking for a low cost simple solution.

I would appreciate any good ideas that would help.

Thanks,

Jim
 
#20 · (Edited)
Jim, I did have some success connecting the ST60 Multi's NMEA+ to RS232 RXD and NMEA- to RS232 GND, *AS LONG AS* the computer was ungrounded. See Actisense's comments regarding not grounding the NMEA- in most cases. With the laptop on batteries or even its AC adapter, it worked fine. However when I plugged the laptop into another device on ship's DC, no more NMEA from the Multi.

Perhaps the IOGear is floating wrt ground (we wish) or you could try the Digital Yacht usb-serial-NMEA reviewed on Panbo:

Panbo: The Marine Electronics Weblog: DY NMEA 0183 to USB, looks handy

List price is about double the IOGear but you'd avoid another adapter.

For a time I used a Noland N183-41 NMEA multiplexer, (discontinued version, borrowed from a friend) which took NMEA in and provided a floating NMEA output as well as RS232. You might find something like that on eBay.

Eventually, I broke down and got the Raymarine E85001... it has the advantage of providing many more sentences, as well as NMEA and RS232 out.

edit: Come to think of it (and re-reading your question), a simple circuit for that application could be simply an Opto-isolator, with a 1K resistor in series with the input/NMEA side (the Multi itself uses 4 2.2k in parallel in series with a PC357 opto) then the opto collector to +12 (with another 1k or so in series for good measure) and the opto emitter to RS232 in. You might need a 10k pulldown or so on RS232, but usually switching from open circuit to +12 would work even without a negative source.

I hope this verbal schematic makes sense, if so it's only about $5-10.
I'm off to bilgeclean and bottompaint but would be delighted to prototype the circuit, test and tweak the resistor values in exchange for help with 46' of wax job. ;-)
 
#22 ·
(repost in case editing my previous post doesn't count as an update)

A simple circuit for your NMEA-RS232 could be simply an Opto-isolator, with a 1K resistor in series with the input/NMEA side (the Multi itself uses 4 2.2k in parallel in series with a PC357 opto, say 560 ohms) .

The opto collector goes to +12 (with another 1k or so in series for good measure) and the opto emitter goes to RS232 in. You might need resistor to ground (a 10k or so) on RS232, but usually switching from open circuit to +12 would work even without a negative source.

I hope this verbal schematic makes sense, if so it should only cost about $5-10. Good luck (from a middle-aged (I wish) EE).
 
#24 ·
Success with ST60 Multi NMEA optoisolator circuit

I have put together a simple output circuit as suggested by Norman and tested it on the boat (see attached JPEG file for diagram).

Some notes - The ST60 Multi's NMEA out + goes thru a 1K resistor in series with an LED (light emitting diode) which in turn is optically coupled to the transistor section of the optoisolator IC (an NTE3041 - $1.49 @ Fry's electronics). NMEA - is the return from the LED.

On the PC serial port side (I used a USB Serial adaptor - IOGEAR GUC232A) DTR (data terminal ready - pin 4) provides the +10v power to the circuit (DTR is only positive when the serial port is open - ex. When the application HyperTerminal is connected). A 1K resistor is in series with the collector of the transistor. The emitter is connected to the receive pin of the serial port (RXD pin 2) and in turn goes to another 1K resistor to ground of the serial port (GND pin 5)

I ran my test at 4800 baud and all waveforms and voltage levels looked fine.

The ST60 Multi provided the following NMEA messages every 2 sec (while sitting at the dock in San Francisco Bay with a little under 20 knots of wind).

$IIDBT,005.0,f,001.5,M,000.8,F*18 (depth)

$IIHDG,185,,,15,E*1A (heading)

$IIHDM,185,M*30 (magnetic heading)

$IIMTW,013.4,C*25 (water temp)

$IIMWV,092,R,016.2,K,A*28 (wind speed and angle)

$IIVHW,199,T,184,M,00.00,N,00.00,K*59 (water speed and heading)

So now that I have the electrical interface working it is on to my software projects.

Jim
 

Attachments

#25 ·
It Works

Hello,

Today I went down to the boat with my laptop and cable. I connected the cable to the Standard Horizon radio (just 2 wires), and connected it to my PC. I started Seaclear and enabled AIS display.

It worked. Very easy to do and it would be helpful when sailing at night, in bad weather, etc.

Barry
 
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