How to output GPS signal to a DSC radio?

[sdowney717]

I have opencpn and the usb GPS is working.
It is running on a PC with Linux Mint
I have a DSC radio that uses I think NMEA.
How do I hook up the radio so that the gps data gets into it?

[bcn]

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

[Franziska]

Pretty sure you can get an answer here if you give more details on the make&model of your radio and GPS. Perhaps also add images of their specific connectors.

[Reefmagnet]

You'll require a USB to RS-422 converter to get an NMEA-0183 feed from the PC. These are available on places like Ebay for a few dollars. Then you need to configure to output the GPS data to the USB device. You'll most likely need to use GPSD if you're also running OpenCPN or anything else on the PC that requires access to the GPS data at the same time, although OpenCPN can be used also to repeat this data if left running all the time.

[sdowney717]

My situation is my very old radio broke, so plan to get one with DSC.
I did not know they were all so very different as to accepting gps data?

I have been looking at getting one of these here.

Cobra Electronics MR F45-D
ICOM IC-M402S

[Reefmagnet]

You could just get a new radio with an inbuilt GPS receiver. Problem solved.
Some radios use NMEA 2000, others use NMEA 0183 and some have both. It's cheaper to interface to NMEA 0183 because it uses essentially non propriety hardware and protocols that don't require licensing which means that specialty ($$$) gateways aren't required in order to get a PC onto the network if using the NMEA 0183 in preference to NMEA 2000. Of course NMEA 2000 has a lot of advantages, but only if you already have, or are planning to have, an NMEA 2000 network on your vessel.

[rgleason]

There is another way to do this.
Use an old gps puck, determine the power wires and provide 5vdc, then determine which wire is nmea in on your radio and connect that to what you think is nmea out on the puck. If that does not work, switch the two nmea puck wires.

This gives your DSC radio a dedicated gps that is not dependent on any other equipment.

[GILow]

One more option to consider. I have not yet made this but it works on paper.

I plan to try getting the NMEA 0183 data from a little M5Stack device I have ordered.

I have nothing downstairs on the boat to give me speed or heading so figured the M5Stack was a cheap and fun solution. Then it occurred to me that I could feed the HF radio at the same time for the cost of a few wires.

Not tried yet but it should work.

[rgleason]

Did not know about m5. There is a gps module acailable. What would you need?
Base, gps, battery, power, nmea?

[GILow]

Originally Posted by rgleason

Did not know about m5. There is a gps module acailable. What would you need?
Base, gps, battery, power, nmea?

Full disclosure, I don't actually HAVE one yet, but my goodness they look good. Lake-Effect brought them to my attention on another thread, and it was love at first sight. I've ordered three of the basic modules, plus one of the GPS modules.

To answer your questions:

Base, well, they are self contained, which is what I liked about them. There's some kind of stand for them for desk placement, but I'll build mine into the timberwork when I am done.

They have built in batteries in all models I THINK, but either way I'd be running from the boat electrics.

The GPS module is a standard part.

NMEA output... I think I will need a chip that does TTL to RS422 for my radio, they are about AU$10 on Fleabay. It will have to be mounted externally, but the device has a Grove port so an external I2C device is no drama.

Cost wise, for my projects, they actually may work out cheaper than doing it all from scratch, since everything I want to build needs a display and control buttons, both of which come with the M5Stack. And the GPS module was good value too, US$26.39 is pretty reasonable.

I've promised to document the builds because, at least at this stage, the M5Stack looks like it might fill a strange little niche in boat electronics for those of us who like simple self-contained devices that are dedicated to one job. I know there are bigger and more powerful platforms, but this one just felt right to me.


Edit: Just noticed this module for the M5Stack.

https://m5stack.com/collections/m5-m...s/commu-module

It does RS485 and I THINK I can put a RS422 receive-only device like my HF radio on the RS485 bus with a bit of care, since I don't need two way communication.

[Lake-Effect]

Originally Posted by GILow

Lake-Effect brought them to my attention on another thread, and it was love at first sight.

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

NMEA output... I think I will need a chip that does TTL to RS422 for my radio, they are about AU$10 on Fleabay. It will have to be mounted externally, but the device has a Grove port so an external I2C device is no drama.

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.

[Moo]

Originally Posted by Lake-Effect

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





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.

Most modern gear will take RS232 straight from a serial port. So just get a bog standard USB to serial cable . Pin 5 is GND and Pin 2 and 3 your data pins... If you don't know which data pin you need touch each in turn onto your NMEA data input wire for on the radio and see which one works.

[Reefmagnet]

I did a lot of experimenting at one point recently with RS422 and RS232 and despite reading a lot about how NMEA 0183 can be compatible with RS232 found the reality to be a bit different using a variety of USB converters. Looking very quickly at the M5 stack specs it looks as if it would be theoretically possible to program the GPIO to transmit a simple null modem data stream, but without an actual UART I'm not convinced it would be a reliable solution long term.

[Moo]

Originally Posted by Reefmagnet

I did a lot of experimenting at one point recently with RS422 and RS232 and despite reading a lot about how NMEA 0183 can be compatible with RS232 found the reality to be a bit different using a variety of USB converters. Looking very quickly at the M5 stack specs it looks as if it would be theoretically possible to program the GPIO to transmit a simple null modem data stream, but without an actual UART I'm not convinced it would be a reliable solution long term.

I have never had one not work... no there was one, a very old GPS that complied exactly with the NMEA specification that would not work with RS232 levels. Other than that the number that I have hooked up must now be in the hundreds going back many many years. I agree if you can get an RS422/USB use that but RS232 will usually work. Disclaimer - telecoms engineer by education who cut my teeth on this stuff so I shouldn't have trouble and what is obvious and simple to me might stump a layman (not referring to you here, but in general hacking this stuff can be problematic).



M5 stack sounds good. I have an ESP module and paperwhite display on my desk here to mess around with. So the same thing in a less user friendly package.

[Reefmagnet]

Originally Posted by Moo

I have never had one not work... no there was one, a very old GPS that complied exactly with the NMEA specification that would not work with RS232 levels. Other than that the number that I have hooked up must now be in the hundreds going back many many years. I agree if you can get an RS422/USB use that but RS232 will usually work. Disclaimer - telecoms engineer by education who cut my teeth on this stuff so I shouldn't have trouble and what is obvious and simple to me might stump a layman (not referring to you here, but in general hacking this stuff can be problematic).



M5 stack sounds good. I have an ESP module and paperwhite display on my desk here to mess around with. So the same thing in a less user friendly package.

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.