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-   -   nmea 0183 to RS232 (http://www.sailnet.com/forums/electronics/61887-nmea-0183-rs232.html)

BarryL 02-08-2010 11:10 PM

nmea 0183 to RS232
 
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

sailingdog 02-09-2010 08:18 AM

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. :)



Quote:

Originally Posted by BarryL (Post 568413)
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


redline 02-23-2010 03:13 PM

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.

ActisenseTechSupport 03-01-2010 05:13 AM

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.

redline 03-02-2010 03:20 PM

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.

ActisenseTechSupport 03-08-2010 04:39 AM

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.

captdale 04-14-2010 10:20 PM

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

sailingdog 04-15-2010 12:43 AM

Quote:

Originally Posted by captdale (Post 593160)
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.

thekeip 04-15-2010 11:35 AM

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

sailingdog 04-15-2010 12:14 PM

Howardó

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.

Quote:

Originally Posted by thekeip (Post 593306)
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



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