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Discussion Starter · #1 ·
Finally got my SH AIS VHF radio. Setting up now. I need advise. I'm connecting an old Garmin 12XL gps to the radio for AIS to work. There are +,-,R and T pins on the 12XL. Should I be connecting the T to NMEA In(+) of radio? What about the NMEA In(-) ? Do I wire the gps "-" , which is the 12V negative, to NMEA In(-) ?
 

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Why not contact Standard Horizon's customer service dept. directly? At the Boat Show in Annapolis a couple of years back they were suggesting that. They would be able to tell you how to connect to a specific device.

Tof
 

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Garmin did a poor job of designing the NMEA 0183 interface on much of their older gear. There is no isolation of the signal ground from the chassis ground.

What this means is that the GPS 12VDC ground should be connected to the NMEA 0183 "-" on the radio.

It also means that you're going to loose the magic smoke if you have a nearby lightning strike.
 

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What this means is that the GPS 12VDC ground should be connected to the NMEA 0183 "-" on the radio.
On the GX2150, the IN- and OUT- connections are inverting inputs and outputs, not grounds, and should most definitely NOT be connected to ground. It won't work, I struggled with this myself.

They should be insulated and left floating.

I think what you need is :

12XL out (T?) to GX2150 IN+
12XL ground to GX2150 ground (green)

Not sure what ground on the 12XL is, could be the - or it could be the cable sheath. You can always measure with a meter.

If you go to the SH website page for the 2150, and click on files, there is a whole bunch of wiring diagrams - not for the 12XL, but many others and should give you the gist of it.
 

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I don't know, I have heard that some units are wired so that the NMEA(-) has to be wired to ground. I have an ICOM MA500TR AIS and a Raymarine E90W plotter and I tried and tried to get the AIS output to be read on the plotter but no luck. I tried many combinations of ++, --, +-, trying different baud rates in the input and output, nothing so far. I shelved the project for now, I got tired of trying. A friend said that he got his to work by tying the NMEA(-) to ground. I think he was also using Garmin, but I plan on trying it next year.

I mean, if it works, then that must be the solution, perhaps lazy engineering on someones part. Has anyone tried using a capacitive coupling between the NMEA(-) and the chassis ground? With a big power capacitor and a small (or no) resistor in series it might solve the problem and still protect the circuit somewhat.
 

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Possibly, but the 2150 is not one of them. No good can come of connecting inverting inputs and outputs to ground.

Did your combinations include : ground to ground, out + to in +, and in + to out +? Because if you never connected ground to ground, that is why it never worked.

I just took a look at the MA500 installation manual, and on page 37 there is a list of pins on the connector.

It mentions GND on pin 1, then - and + outputs. A common misconception is that the minuses are grounds. At least on my GX2150, they are inverting inputs/outputs.

So connect pin 1 (ground) to the plotter ground. (might be a wire, might be the cable sheath)

Then connect plus to plus, both ways : plotter o/p + to MA500 in +, and plotter input + to MA500 out +. Simple.

I've had to work through all these issues myself when I first connected up my GX2150. I ended up consulting a highly expert electronics engineer. What SH have done is provided two separate inverting and non-inverting, labelled - and +, inputs and outputs. In this case the - ones are simply left unused. It is NOT a bipolar or balanced input, when grounding one or adding a capacitor would otherwise help.
 

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Here is a typical scematic (not necessarily yours) from the chart plotter's perspective;


Here is a typical scematic (not necessarily yours) from the radio's perspective;


NMEA 0183 out from the GPS is BLUE, and the signal's reference voltage [designated "NMEA IN (-)"] is Ground.
 

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Discussion Starter · #10 · (Edited)
OK, I've got my 12XL to talk to the GX-2150.
NMEA In+ -> gps "T" NMEA transmit
NMEA In- -> gps "-" negative pin of 12V.
Unfortunately I'm not able to upload the picture of 12XL satellite signal and GX-2150 satellite signal page as evidence.
 

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Yes, out(+) to in (+) and out (-) to in (-) was certainly my first connection. When that didn't work I started to look at other combinations. Other combinations might work because manuals have been known to have pin outs labeled wrong.

I'll have to look at the manuals and take a closer look at ground connection possibilities, I don't remember how I connected grounds, but that doesn't mean they weren't connected. I'll check the manuals after the weekend and try to remember what I did.

Just for troubleshooting, does anyone know of any tell tale way to identify each pin using a DMM? That might be a really useful piece of information for folks trying to figure out if the pin out in a manual is accurate.
 

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You will need an o-scope, as MarkSF points out, to watch the bits on the wire, or you could connect it to the serial port of a PC to interpret the NMEA 0183 sentences. The "signals" on NMEA 0183 are actually +5v binary pulses, from EIA-422 (similar to RS-232) at 4800bps - or 38,400bps for NMEA 0183HS.

For more fun, see NMEA 0183 - Wikipedia, the free encyclopedia
 
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