They won't talk to each other! (GPS and VHF)

This one is for all the gurus on this site.

I've been trying to get my Garmin GPSMAP 478 chartplotter to "talk" with my Uniden UM 525 VHF Class D radio. The idea is to get DSC functionality.

The Garmin power/data cable has the following leads: power (red); ground (black); alarm (white); voice + (brown); voice - (orange); data out (blue); and data in (yellow).

The radio's GPS connector harness has the following leads: NMEA 0183 out - (orange); NMEA 0183 in - (yellow); NMEA 0183 out + (green); NMEA 0183 in + (white); not used (red); not used (black); external speaker + (brown); and external speaker -/ground (blue).

Both the chartplotter and the radio support NMEA 0183 version 3.01.

I configured the serial data format on the chartplotter as NMEA IN / NMEA OUT. I connected the blue lead on the chartplotter to the yellow lead on the radio, and the yellow lead on the chartplotter to the orange lead on the radio. I tried reversing the leads. I also tried the green and white leads on the radio, and every combination of the above.

Reading the manuals causes me to question whether the units employ the same "sentences" (whatever those are) but I'm not sure about this. Anyway, one would think that NMEA 0183 version 3.01 on the chartplotter is the same as NMEA 0183 version 3.01 on the radio.

I'm fresh out of ideas. Any wisdom would be greatly appreciated - even if it's a suggestion on how to troubleshoot or a recommendation of another site that might be savy on these issues (though my confidence in fellow Ericson owners is absolute!).

If you've made it this far, thanks for reading...

Wiring hint

Go blue GPS to orange on the radio harness and make sure the black is common. Do not worry about NMEA out on the radio, it can't tell the GPS anything useful. Happy wiring. Ryan

Rssailor,

Thanks, but I've already tried blue (chartplotter) to orange (radio) and a myriad of other combinations. Not sure what you mean about making sure the black is common, though. Both the radio and the chartplotter are grounded to the same bus inside my DC panel. The "black" lead on the radio harness is "unused" - which I assume means that the wire is not connected to a pin on the connector fitting.

I've probably missed something so obvious that it's absolutely imperceptable to me. I hate that...

The Garmin Game

Try this, it should work.

The Garmin ground (black); To radio's GPS connector NMEA 0183 in - (yellow)
The Garmin data out (blue); to the radio's gps connector NMEA 0183 in + (white)

Make sure that the Nema on the Garmin GPS unit is set to NEMA/NEMA and that the baud rate is set to 4800 baud.

That should take care of the issue. If not let me know.....

Nothing to do with sentances should be required unless you have changed them already in which case you would need to change them back.

The issue is in the specs for NEMA and the voltages and ground paths on Garmin devices. This is a common issue Yes the ground really does need to connect to the NEMA in -, regardless of where it goes to the panel ground. The ground on the Garmins has to be connected in the NEMA loop to work, otherwise you end up with a floating ground on the Garmin NEMA output which results in the inabilty of the radio to distinguish a high state from a low state on the Nema input. By tieing the Garmin ground to the radio NEMA - you tie the NEMA output low state to a common ground.

If you want me to explain floating grounds more than that we are into consulting time, and well then you would have to be buying gin and tonics....

The other common issue is users not setting the interface setup options correctly, they ship from the factory as Garmin/Garmin, which is an interface option that won't talk to NEMA devices....

Guy

Guy - Wow, I think you've already earned that G&T (Bombay Saphire, at least!).

I don't know if this is going to get me into real consulting time or not, but one more question, if you please.

Since my Garmin is already grounded to the common bus inside my DC panel (and is functioning) can I just run another wire from the ground bus to the radio's GPS connector NMEA 0183 in - (yellow)? If not, will the Garmin be properly grounded if I run the ground wire only into the radio's GPS connector NMEA in - (yellow)?

Many, many thanks...

To second Guy's comment about the factory set up - I had this same problem with a Magellan GPS and just about went over the edge trying to figure out what I was doing wrong. Then I noticed in the Magellan set up process a box to turn the NEMA output OFF or ON. Not sure why you would ever want to turn it OFF, but setting it to ON was all it took to make everything and everyone happy. Let's hope yours is presently turned OFF.

You could, but better to not

Rob said:

Since my Garmin is already grounded to the common bus inside my DC panel (and is functioning) can I just run another wire from the ground bus to the radio's GPS connector NMEA 0183 in - (yellow)?

Click to expand...

You could do it this way, and in theroy it make little difference, but in practice it seems to increase the noise on the nema side. Depending on how far away your units are give it a shot and see what happens. The Garmin still needs to be conneceted to ground not just to the NEMA connections on the radio.

Guy

There are a few things to know:
Uniden and Garmin have talked to each other for a long time.
The NMEA 0183 standard has been in use for the same time.
They DO work well together. This may sound elementarybut for troubleshooting purposes, it's necessary (and comforting) to know you're not dealing with an engineering problem.
Some devices in the 0183 network are basically input devices...that is, they listen. Examples, for your situation are: The Uniden is an input device; the chartplotter is an input device; a radar display, if you're using the display as your plotter, is an input device. Any reference to color is misleading...it's the function that's important.
Some devices are output devices; the Radio is NOT an output device; nor the plotter. The Garmin IS, however, as is the fluxgate compass if you have one, or the depth sounder. If you're using the chartplotter as your display, the radar may be an output device.
The basic theme here is to determine which of your devices is listening (for data), or talking (supplying the data).
Connect the cables, or conductors exactly as the manufacturer of the individual devices says and realize that the DC ground may not be and shouldn't be the same as signal ground. (This is where I'd look to solve your problem).
When you think you have communication established, that's when you should tackle the sentence structure and syntax.

howard Keiper

Garmin uses Power Ground as Signal ground on ALL UNITS

See page 118 of the owners manual, connect the radio exactly like it shows to connect the autopilot in that diagram.

Battery ground is signal ground on the majority of the Garmin product lines. Not usualy considered the best engineering, but the way that it is.

If you don't have the owners manual you can get it here:
http://www.garmin.com/manuals/1130_OwnersManual.pdf

Which is exactly like I described above. However it is a good thing to look at the manual whenever you can. (Although too much of that can get you kicked out of the manly man club! )
Thanks,
Guy

Sweet success!

Thanks to the good advice here, I'm up and running.

Just as suggested, I connected the radio's NMEA "in -" and NMEA "out -" to the Garmin's power ground (but well upstream of the DC ground bus). Lo and behold, it works!

Funny - I did stare at the wiring diagram in the manual for some time, but I just could not "get" the signal ground concept. With the benefit of the context provided by the explanations on this board, well, it's obvious!

To the administrator: If I'm ever caught dispensing electrical advice on this site, my account should probably be suspended...

Thanks to all.