How to output GPS signal to a DSC radio?

[GILow]

Originally Posted by Lake-Effect

I think it was another poster, and I just chimed in with my 2 cents.

Oops, my bad. Yes, it was conachair.

Originally Posted by Lake-Effect

Check with your radio manual to confirm whether it insists on official RS 422 or will grudgingly accept something close - like unbalanced, or pseudo-balanced, which means just inverting the one output to make the second; something that can be done with almost any logic gate or a very simple one-transistor inverter.


It would be good to have a play with your new VHF on the bench before installing, to explore your options for the GPS feed.

It's an ICOM 802, I am sure there have been some discussions about feeding it GPS positions here on CF; I'll have a look.

[Moo]

Originally Posted by Reefmagnet

That may be so, but later derivatives of the NMEA 0183 specification specify RS422 which has advantages over RS232. If you need to add a converter anyway there's little justification in choosing RS232. About the only caveat I can think of is the wiring is a little more complex due to RS422 not technically having a ground.

That is because the original NMEA0183 was a specification in its own right. physical and electrical as well as the other levels in the stack. It was brought into line with an RS specification as the parts were easier to source, no need for custom chips etc..



I do not disagree that you can should preferably use a purpose built USB/NMEA 0183 interface or RS422.. But USB/RS422 devices are very difficult to find in many parts of the world, where USB/Serial are available even on a tiny Pacific atol.. Because of my background I go with devices that are readily sourced wherever you may be sailing ...

[GILow]

Originally Posted by Moo

Because of my background I go with devices that are readily sourced wherever you may be sailing ...

This is good advice.

I have tried to manage the risk by standardising my hardware platform and buying spares of the various chips I use once I have the device working. Mostly they are very cheap and come in airtight anti-static bags which helps.

[sdowney717]

Ok appreciate the discussion, another way I might go is buy a nmea gps
It has 4 wires, black and red is 5vdc power
Uses nmea 0183, greenwire is tx uart and white wire is rx
https://www.aliexpress.com/item/3285...chweb201603_52

I can power the gps from a 12vdc to usb charger plug.

I did buy the MRF45D vhf Cobra radio from Amazon.

The instructions are simply this,
To Install A GPS Device:
1. Install the GPS device in a convenient location
according to its manufacturer’s directions.
2. Bond the NMEA out negative wire to the black
wire of the GPS interface cable.
3. Bond the NMEA out positive wire to the red
wire of the GPS interface cable.

So which color from radio to which color from gps?
I suppose green and white on gps but to which colors the radio
So on gps which is nmea out positive and negative?

[sdowney717]

I dont think it will work like that, maybe not at all.
I think I want only the tx wire from GPS to go to red input wire on radio, the negative black wire is shared between gps and radio
But the voltage of the radio is 12v, and this gps is 5v

Does anyone know?

[GILow]

Got a multimeter? Just check the voltage the radio is delivering. 3.3 to 5 volts, all good. 12 volts, then just wire in a little LM7805 chip.

Edit: had a look at the documentation for the radio. Could not find a spec on the output voltage, but even if I had, I would always check with a multimeter before connecting anything up. So often the manual turns out to be wrong on little details.

[sdowney717]

ASFAIK there is no output voltage on the NMEA line worth any help.
I am pretty certain now the 12v GPS on AliExpress will work now.
https://www.aliexpress.com/item/3291...3da24c4d7M4E9q

I notice they have a wiring diagram for a similar gps here, and it lists my Cobra radio. And it looks like wire info is very much the same, the thick black is ground for power, while the thin black is NMEA negative. Green is NMEA positive.

4800 baud is what marine vhf are looking for in gps data.
I can see why so many DSC capable radios are never hooked up to a gps, it is very confusing.
And on a PC, the strict rs232 protocols were not designed to work with NMEA rs422 but they sort of do work.

https://www.ebay.com/itm/GPS-RECEIVE...-/222689774453

[barnakiel]

Depending on your kit, you have either 3 or 4 wire signal. This applies to both the gps and the radio end (each can have a different number of wires).


The 3 wire set up is called rs232. (simplification)



The 4 wire set up is called rs422. (as above)



Connecting 3 wire gps to 3 wire radio is simple.


Connecting 4 wire gps to 4 wire radio is nearly as simple.


Connecting 3 to 4 or 4 to 3 is often done with an interface piece.


In the simplest scenario (3 / 3) connect gnd to gnd and gps 'out' to radio 'in' data wires.


Plenty of google material to read into any more complex set up, e.g.


https://nolandeng.com/downloads/Interfaces.pdf



Cheers,
b.

[rgleason]

RE: Using a Puck. With my old Globalstar BU-353 Receiver (which does not work with Win10), which I used for this purpose, I had to use the GPSinfo program from the manufacturer, to set the GPS Puck into "Serial Mode" otherwise there was no output of Nmea that could be used.

This may also be true with other Pucks.


Also the puck receives a good signal from under the cabin top next to the companionway. Velcrod to the underside of the cabin top.

[GILow]

Guys, the OP linked to a puck that is limited to 5 volts input. Although I would not EXPECT the radio to put out more than 5 volts on the GPS plug supply wire, we cannot ASSUME this is the case.

Needs to be tested otherwise the puck will possibly be fried.

This is said from the perspective of someone who plugged a DS180B20 into the wrong side of his LM7805 chip a few weeks back and ended up with a smoking hot and very dead sender.

[Reefmagnet]

GI, I plugged a 12VDC supply into an external USB DVD drive a while back. Then I plugged it into my very $$$ not that old laptop computer. It was at the point that the laptop went instantly dead that the penny dropped that I should have plugged a 5VDC supply into that DVD drive.


Be that as it may, the NMEA signal wires shouldn't care about supply voltage? And 12 to 5 volt power supplies are a dime per dozen.

[Spot]

With everyone's help, I had success hooking a Garmin GPS to OpenCPN via NMEA 0183 and serial to USB converter here:


http://www.cruisersforum.com/forums/...sb-218908.html


It is also a situation where +5VDC from USB/computer was kept separate from +12VDC going to the GPS.

[GILow]

Originally Posted by Reefmagnet

Be that as it may, the NMEA signal wires shouldn't care about supply voltage? And 12 to 5 volt power supplies are a dime per dozen.

Not sure about the NMEA voltages side, I still have a lot of learning to do there before I start smoking components.

I just noted that the puck that the OP was planning to use required 5 volts, and it would normally source that 5 volts from the GPS plug on the radio. The radio manual, rather stupidly, recommends that you connect your gps to the red and black wires, but does not actually say what voltage you will get for your troubles.

Simple enough to find out with a multimeter, and I would argue that if the OP does not have a multimeter then they probably shouldn't be trying to hook this stuff up, unless they don't mind the smell of fried puck.

[Dockhead]

Originally Posted by bcn

Starting with studying the manual/documentation of the radio?
Nobody will be able to answer you that kind of generic questions...

It's not a generic question at all. All DSC radios which don't have their own GNSS receiver work the same with either 0183 or N2K input for the position data.


To the OP:



There are two simple ways to do this:


1. Buy a radio with built in GNSS receiver, as someone suggested. Job done. This is the best way to do it IF you like one of those radios available. Here's a good one: https://bestmarineradio.com/standard...e-radio-white/


2. Buy a separate GNSS puck for the radio which outputs 0183; make sure you are using a radio which takes 0183 as 99% of them do.



Then the complicated way:


3. Faff around with trying to share your computer's GNSS datastream with the radio. You can do it with an RS-422 converter and fiddling with the data type and ports, but it will cost you more money and 20x more time than one of the variants above. GNSS receivers are so cheap that it's not worth all this trouble to try to share it between two devices which are not already networked for other purposes.




Here's the way most people do it:


4. Connect a chart plotter with dedicated 0183 talker port to the radio with two wires. Or connect the radio to an N2K network if it has an N2K port. Job done, because the gear is all designed to be connected this way. You are suffering complications because you are using a computer rather than purpose made marine chart plotter.

[smac999]

If you are buying a new radio. Just Get one with built in gps.