How's that for alphabet soup?

Here's my problem: I've got an older Uniden 525 UM VHF that's DSC enabled. I used to have it connected to a Garmin GPSMap C-276 for GPS data which worked great (the GPS was also connected to my auto-pilot, but that's a problem for another day). I've replaced the older Garmin for a new Garmin EchoMap 54 DV chartplotter and I can't for the life of me get the radio to see the GPS data from the chartplotter. I've got the serial port on the GPS set to either standard or high speed NMEA 0183, and outputting data sentence GPRMC which should be enough to provide GPS position, speed, etc. to the radio. I can run diagnostics on the GPS and see that it's outputting what I think are the right sentences, but no matter what I do, the VHF doesn't see them. The GPS is displaying what seems like a valid position, and the boat indicator shows my boat in the right spot in the world on the chart, so that seems to be working.

The VHF has two channels for NMEA data, and the GPS only has one pair of NMEA 0183 wires. The VHF lists them as Data In + and Data Out + or Data In - or Data Out -. The GPS lists them as simply data in and data out with no +/- associated. I've tried both channels on the VHF with the cables attached as it seems like they should be, and reversed. In either case, I can see the diagnostics outputting the GPRMC sentence.

I am at a loss as to what to try next, but maybe I'm also missing something obvious. I worked until I ran out of light (and my back was killing me from being in a half-stoop most of the afternoon). Poor Rita spent the whole afternoon cooped up in the cabin listening to me swear.

Ideas?

The one plan I have for tomorrow (assuming you guys don't propose a better one) is process of elimination. There are two pairs of wires coming from the radio, and one pair of wires coming from the GPS, I can create a matrix in Excel or something and just try every possibility.

At least I was able to get the GPS mounted on the swing arm I bought for it and wired up to work just as a chartplotter. I also have the transducer mounted and ready to be used, but it's going to require a bit more work to get the cable run through the interior of the boat and up to the chartplotter.

You better contact NASA for this one.

I've had to turn off some outputs to get the Nema sentence just right for the instruments to get the data.

It's been a few years but I think we had B&G hydra. Might have been the gen before that. The gps was a newer garmin and was spewing out more than the B&Gs could handle.

Looks like you already reduced the sentence so I'm not sure what else to try other than the wiring.


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I might try this, turn off all the sentences I don't think it's using (there are still a bunch turned on).

Yall really should be seeing yalls doctors about those finger spasms yall suffer from...

Did you make your own cable or buy one? Are you sure the pins are outputting the proper signal levels? Ie are they both TTL or RS-232 levels?

You should have 3 wires, RX, TX, and ground.

The adapter will cross those wires, TX on the GPS goes to RX on the VHF, RX on the GPS goes the the TX on the VHF, and gnd is gnd...

If your connections are data in + and data in -, and data out + and data in - the ground may be isolated... I'd use an ohmeter and check resistance between data in - and data out -....

Also, in terns of the NMEA sentence structure, new sentences were added on newer versions. I've had issues in the past with older GPS units not sending out a particular NMEA sentence and the device failing to recognize GPS is attached. I have had systems that ONLY require 2 or 3 sentences, but had ALL of them enabled, and the device just ignored the sentences it didn't require..


4800 baud is standard for NMEA, high speed would be 9600, IIRC..

^^^^^ Hope that helps..


If they are, it may be a configuration issue or lack of specific NMEA sentence.....

EDIT: Misread what equipt was being used...

I'm reading that the wiring needs to be:

GPS - Radio
Brown - Green
Blue - White
Black - Orange and Yellow

Not sure why the radio has separate grounds for the data Tx and Rx but the GPS has a common ground for those.

Page 43 of the radio manual shows the nmea info it supports and what takes priority:

http://phone.manualsonline.com/manuals/mfg/uniden/um525.html?p=43

Shit. I misread what equipt he was using....

Here's what I got..

That looks right to me. Your line colors might be a little confusing.

I didn't include power in my description. The GPS has separate power inputs but the radio uses the same wire as the data input/output.

I figured that part was sorted out since the radio comes on.


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Guys, thanks for doing the research and offering advice, I really appreciate it. I got a bit more fried in the sun yesterday than I thought (Rita's amused because she told me to goop up with sun screen, but I thought it was late enough in the day to not worry about it, should have listened), so I took the day off from boat chores today. We're taking the boat out tomorrow with friends to go view the eclipse, and Rita & I will be staying afterward to see if we can get the GPS / VHF connection working.

I tried connecting the VHF blue to the GPS black (ground) yesterday afternoon, but that didn't seem to help. However, by the time I tried that, I was pretty brain fried and there wasn't much light left to work with anyway.

I'll let you know how it goes tomorrow, and thanks again.

I've taken your diagram (thanks very much for combining the two wiring diagrams and drawing the connections), and put it into a spreadsheet & printed it out to bring with me tomorrow. I did the same thing with the previous GPS and left it in the panel ( had to extend my original cable by about 10' so I used some CATV cable to do so, which worked well for the past 8 years or so). Hopefully you guys nailed it and it only takes 10 minutes to get it working.

Thanks again.

Ground loops are bad.
Had a customer with a shop a couple hundred feet from his house, had a buried coax thin Ethernet cable between them.
Lost connection to the server.
I unplugged the coax cable to do a test, saw a spark and it shocked me.
90V potential between the chassis ground from the server to the chassis ground on his remote computer.

With only four wires coming out of the GPS the ground has to do double duty (triple if you include separate Tx and Rx grounds)

Seems like that would put a lot of noise onto the data signal but I guess they have it figured out.

I mean, you pay 3 times the cost because it has 'marine' in the name, it must be bomb proof right?