Connecting GPS to wheel pilot and DSC VHF

[Carter Brey]

Hello, you electrical engineers.

I just finished installing a second DC distribution panel and have run cables from it to a terminal block back in the portside cockpit locker, behind a protective wooden cover and next to the original factory-installed terminal block. This panel is for DC power to the non-handheld Garmin GPS and the Simrad wheel pilot and its remote control.

I also want to connect the Garmin GPS output to my new Uniden Solara DSC VHF, which is not involved with the new distro panel.

I'm a little stumped by differences in NMEA port terminology used by Garmin, Simrad and Uniden. I'm hoping some of you might have dealt with this and know what connects to what.

Example: Garmin units, in addition to the usual DC + and DC-, label their NMEA data ports as "NMEA OUT" and "NMEA IN". In the case of my unit, a 172C, there are two sets of these. According to their diagram, the first pair is labeled parenthetically as "Com 1 Tx (NMEA OUT)" and "Com 1 Rx (NMEA IN)". These they indicate should go to the autopilot or other nmea device. The other pair, parenthetically labeled as "Com 2 Tx (NMEA OUT)" and Com 2 Rx (NMEA IN)". They indicate that these should go to and from the DSC VHF. Okay, I understand this, it makes sense so far. The DC negative is also labeled "Ground (power and data)". Here is what the diagram shows:

Red: 10-35v DC
Black: Ground (power and data)
Blue: NMEA OUT (Com 1 Tx)
Brown: NMEA IN (Com 1 Rx)
White: RTCM/NMEA IN (Com 2 Rx)
Green: NMEA OUT (Com 2 Tx)
Yellow: Alarm low

However, the Uniden VHF diagram shows the ACC cable with the following labels:

Thick black: DC GND
Orange: External speaker +
Black: External speaker - GND
Green: GPS data in
Brown: GPS GND
Yellow: NC

Disregarding the external speaker wires and the yellow wire, it's clear that the "Com 2 Tx NMEA OUT" from the Garmin GPS should connect to the Green wire on the VHF ("GPS data in"). But the brown wire? GPS GND? What is the equivalent on the Garmin GPS? The only wire labeled "ground" on its cable is the black DC negative, called "Ground (power and data)". Is that what the "GPS GND" on the VHF should connect to?

Now, on to the Simrad WP30 wheel pilot. It's a little complicated because the wiring with the handheld remote control is different from the wiring without. The remote comes with a four pin socket from which issue six wires. Here is what the diagram with the remote control says:

Green: NMEA Com from GPS
White: NMEA data from GPS
Red: 12v DC
Black: 0v
Blue: NMEA Com - autopilot
Yellow: NMEA Data - autopilot

There is a note in the main autopilot manual which says: "It should be noted that some manufacturers' equipment does not have a dedicated Common connection. In this case, the DATA connection will usually be labeled NMEA OUT, and the NMEA Common connection on the wheel pilot (blue) should be connected directly to 0v (black)." Does this mean that, when connecting my remote control wires, the green ("NMEA Com from GPS") should be connected to the DC negative? It at least seems obvious that the White ("NMEA data from GPS") is connected to the "NMEA OUT (Com 1 Tx)" from the Garmin GPS.

So... I guess my basic question is this: anytime the NMEA devices (autopilot, remote control, or DSC VHF) require a "common" or "ground" connection, does that go to the DC negative return?

Sorry, this must be a bore to sift through.

Thanks,
Carter

[seadawg]

Good morning Carter,

Maybe this will help a little. I just installed a Uniden UM525 W/DSC and a Garmin 76C. I had trouble understanding the Uniden wiring drawing and had to call them. What we came up with is as follows:

The Ship ground buss, the GPS ground (black) and both serial data (-) are connected together. The GPS serial data out(brown) connects to the VHF serial data in (white) and the GPS serial data in (white) connects to the VHF serial data out (green). The wire colors probably are not the same for you. I hope I'm reading your question right. The installation worked very well. Cheers

[seadawg]

Please let me revise the above post as "The ship ground buss, the GPS ground (black) and both VHF serial data (-) are connected together."

[John R.]

Hi Carter,

I see your interfacing as follows:

Garmin BLUE to:

Uniden GREEN
Simrad WHITE

Garmin BLACK to:

Uniden BROWN
Simrad GREEN

The GREEN from your GPS (com grnd for RTCM) should not be connected.

Disclaimer: I am not absolutely positive about interfacing a Garmin unit to a Simrad (Navico) pilot computer, but review of your notes indicates the above to me. The problem with NMEA is just what you have experienced, non-standardization across the manufacturers with various labeling and wire color indicators. NMEA 2000 as a ethernet was supposed to eliminate these issues and of course only some manufacturers are using it. Realize it is now 2007 and NMEA 2000 is already seven years old and still not widely used by manufacturers. However, you will see expansions of proprietary systems like Seatalk. Manufacturers want the edge, not to just be a nother dog in the show, rather they wish to be the show champion. In NMEA circles this is the root of the problem. Manufacturers will not cooperate because they are afraid to lose their individual market share. At least all of your components are sharing NMEA 0183 I assume. That makes it much easier. It's when you have to use old with new, mix protocols, use multiplexers that things can really get screwy. Good luck, hope it works. If not, call Simrad for clarification.

[Carter Brey]

There's light at the end of the tunnel.

Yes, all these devices use the NMEA 0183 protocol.

Carter

[John Danicic]

[quote]quote="Carter Brey"]There is a note in the main autopilot manual which says: "It should be noted that some manufacturers' equipment does not have a dedicated Common connection. In this case, the DATA connection will usually be labeled NMEA OUT, and the NMEA Common connection on the wheel pilot (blue) should be connected directly to 0v (black)." Does this mean that, when connecting my remote control wires, the green ("NMEA Com from GPS") should be connected to the DC negative? It at least seems obvious that the White ("NMEA data from GPS") is connected to the "NMEA OUT (Com 1 Tx)" from the Garmin GPS.

Carter:
As I remember, I connected that Blue Simrad NMEA common wire to the boat's ground wire. A bit confusing language. Glad I wasn't the only one who had to puzzle through it.

But what really made it work for me was the following.

I too have a Garmin, a GPS Map76. In order for the GPS and AutoPilot to communicate with each other:
In the GPS, go to
"Main Menu" select
"Setup Page" - go to the
"Interface" tab - and then select
"NMEA" from a bunch of names.

When you download your GPS maps or updates, this setting needs to be on "GARMIN" not "NMEA". Your GPS may have a similar setting.

We live in the day of the tower of techno Babel.

I hope you get her working smoothly.

Sail on.

John Danicic
CD 36 - Mariah - #124
Lake Superior