Garmin 545s & Autohelm ST4000 & NMEA

[db27513]

Im trying to connect my 545s to my ST4000. Has anyone done this? The Garmin says to use two wires to connect to a NMEA device: a Blue NMEA out wire (positive), and a ground. The ST4000 labels its NMEA inputs as Data in +ve (a red wire) & Data in -ve (a blue wire).

The problem? Garmin calls its blue wire as positive (RXD+) while Autohelm says the blue wire should be negative. Autohelm also doesnt mention anything about grounding the other lead..

Any clues?

Thanks
Dave in NC

[thekeip]

NMEA 0183 devices are generally connected as 'talkers' or 'listeners', depending on their function. There are exceptions, but the AP expects to get data from somewhere and is, therefore, a listener...it doesn't produce data. The GPS on the other hand, is primarily an output device...for the purpose you're concerned with, it is a talker, providing data to the AP.
It would be a good thing for you to use a two or three terminal barrier strip to make your NMEA connections. Ignore the colors. Connect the talker's output to the listeners input..(+) to (+); connect the talkers (-) to listeners (-). Initially, don't assume that either (-) is ground.
Howard Keiper
Berkeley

[sailingdog]

Dave—

The problem is that Garmin uses the 12 VDC ground as the signal ground. So, to get it to work with the ST4000, you need to connect the Garmin (Blue or Grey) NMEA out wire to the ST4000's RED NMEA+ in wire, and then you have to connect the ST4000's BLUE NMEA- wire to the Garmin's 12 VDC ground.

Be aware you probably need to set the Garmin's serial port to the NMEA 0183 protocol, as they are set to Garmin's proprietary protocol by default IIRC. Set the ports to NMEA 0183, 4800, 8, N, 1.

Originally Posted by db27513

Im trying to connect my 545s to my ST4000. Has anyone done this? The Garmin says to use two wires to connect to a NMEA device: a Blue NMEA out wire (positive), and a ground. The ST4000 labels its NMEA inputs as Data in +ve (a red wire) & Data in -ve (a blue wire).

The problem? Garmin calls its blue wire as positive (RXD+) while Autohelm says the blue wire should be negative. Autohelm also doesnt mention anything about grounding the other lead..

Any clues?

Thanks
Dave in NC