NMEA hookup question

walt

.
Jun 1, 2007
3,511
Macgregor 26S Hobie TI Ridgway Colorado
I want to connect my Garmin chart plotter to my Raymarine ST2000 auto pilot

The Garmin has a NMEA 0183 Rx and Tx data lines. Ie, one wire for the Rx and one wire for the Tx.

The Raymarine ST2000 has an input NMEA set of wires noted as NMEA + and NMEA - which get connected to an instrument with an NMEA output.

The NMEA + and - is a little confusing as this implies a "differential" input. The chart plotter does not have a differential Tx, only a single wire Tx output. So I am assuming that I would connected the chart plotter Tx line to the NMEA + input line on the Raymarine ST2000 and then ground the NMEA - line on the ST2000. The ST2000 manual calls this input on the ST2000 NMEA 0183. Or.. do I have this wrong?

FYI, assuming the NMEA - input does get grounded, I think the ST2000 NMEA - input will get its ground from the chart plotter ground over the data transmission cable rather than using the ground on the power input to the ST2000.
 
Last edited:
Oct 24, 2010
2,405
Hunter 30 Everett, WA
I'm guessing what you call NMEA from your ST2000 is NMEA 2000. The NMEA 0183 coming from a Garmin needs the negative wires grounded when interfacing with other brands of equipment over NMEA 0183. If your ST2000 is NMEA 2000, you will need to purchase an adapter. If it's NMEA0183, I'd connect it, ground the negative leads, and try it.

Ken
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
If you have your wires sized they will be at the same potential. So TX- will be at ground. With 183 you connect the talkers TX to line to one or more RX line one the listener(s).

The ST2000 is way too old to be NMEA2000.

Les
 
Oct 24, 2010
2,405
Hunter 30 Everett, WA
If you have your wires sized they will be at the same potential. So TX- will be at ground. With 183 you connect the talkers TX to line to one or more RX line one the listener(s).

The ST2000 is way too old to be NMEA2000.

Les
With Garmin, the negative leads need to be grounded or it will not interface with other brands. This is a poorly published fact.

Ken
 

walt

.
Jun 1, 2007
3,511
Macgregor 26S Hobie TI Ridgway Colorado
NMEA from your ST2000 is NMEA 2000
The ONLY mention of NMEA in the ST2000 manual is 0183. I have checked several times..

The pins on the ST2000 are:
1. 12V
2. ground
3. Not used
4. SeaTalk
5. NMEA -
6. NMEA +

The ST2000 autopilot is LISTEN only so is a Rx and would normally connect to a Tx signal on the chart plotter. But it appears that the NMEA Tx on the chart plotter is a single line and the Rx on the ST2000 is differential. The single end to differential is the question in the original post. I am still searching by google as this has to be an old problem..
 
  • Like
Likes: justsomeguy

walt

.
Jun 1, 2007
3,511
Macgregor 26S Hobie TI Ridgway Colorado
Just connect NMEA- to ground.
Yep.. I will still use a two wire data cable. At the Garmin chart plotter side, Tx will be one wire of the two and ground taken at the chart plotter side will be the second wire.

At the ST2000 auto pilot side, the Tx wire will connect to NMEA + and the second wire will go to NMEA -.

Assuming this is how it all works.. I dont think I can burn anything out trying this so I will hopefully in a few days.
 
Oct 24, 2010
2,405
Hunter 30 Everett, WA
You may still need to connect the negative input wire from the autopilot if it's a differential input. It won't hurt anyway.

Ken