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Noob question: NMEA gps out to vhf marine radio?
#1
I've got OpenPlotter running on RPi3B+. I have an older Standard Horizon vhf radio that will accept NMEA0183 gps in to enable it's Distress function. Can I set up a usb connection from the pi to the vhf radio? I've seen this cable at AdaFruit and was wondering if it would serve to establish a working connection to send NMEA to the radio:

USB to TTL Serial Cable - Debug / Console Cable for Raspberry Pi product ID 954
https://www.adafruit.com/product/954?gcl...KLEALw_wcB

That is,  if I plug the usb-A end into the RPi running OpenPlotter, and wire the free end to the gps-in wires of the vhf, will this work?  

Or is this too complex?  Should I instead take the raw serial data from a usb connection configured for gps out from Kplex, and send it directly to the vhf radio? I could do this with a usb A male 5 pin terminal block, but I need a clue as to which pins to tap.   

Thanks in advance for some help with this!
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#2
First of all OP will definitedly output NMEA0183 to your VHF with the right hardware, but I don't think the product you are looking at is going to work for your application.  But I could be wrong, maybe someone with more knowledge will speak up.

The old manual talks about NMEA0183 output (new one in work). It is still relevant.

https://sailoog.gitbooks.io/openplotter-...erter.html

You need something more like this for what you are trying to do:

https://www.amazon.com/Serial-Converter-...GBM5BR6R4G

Good luck!
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#3
Thanks for replying! I feel like I'm on the right track now.  The Standard Horizon vhf should be a slam-dunk if you're right about the RS-485/RS-422 protocol being the way to go.  

If I'm understanding correctly, because this radio only wants to accept gps sentences, and the wiring is only two strands, it must be half-duplex.  If that is the case, what do you think about this CH340T based dongle, at less than half the price.

https://www.amazon.com/JBtek-Converter-A...27KYJ19G33


We're not looking for speed in this application.  I think I'm going to give it a try.

If this works for the OP to vhf link,  I'm going to try it to link OP to an old Raymarine autohelm radio navigation interface next.  I'm much less certain of making that work, for lack of clarity on just what sentences to direct to it. (See my post from yesterday).

Which raises another question in my mind:  It looks like RS485 can connect a number of devices in parallel? Does that mean I could tap this same dongle in parallel to tie in that radio interface?  The autohelm interface is also receive only, and I believe it only responds to cross-track error sentences (dead-reckoning, not measured). So, it, too, should work in half-duplex.

So much to learn!
What do you think?  Thanks again for your help.
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#4
(2019-05-25, 09:11 PM)skyeyedoc Wrote: Thanks for replying! I feel like I'm on the right track now.  The Standard Horizon vhf should be a slam-dunk if you're right about the RS-485/RS-422 protocol being the way to go.  

If I'm understanding correctly, because this radio only wants to accept gps sentences, and the wiring is only two strands, it must be half-duplex.  If that is the case, what do you think about this CH340T based dongle, at less than half the price.

If this works for the OP to vhf link,  I'm going to try it to link OP to an old Raymarine autohelm radio navigation interface next.  I'm much less certain of making that work, for lack of clarity on just what sentences to direct to it. (See my post from yesterday).

Which raises another question in my mind:  It looks like RS485 can connect a number of devices in parallel? Does that mean I could tap this same dongle in parallel to tie in that radio interface?  The autohelm interface is also receive only, and I believe it only responds to cross-track error sentences (dead-reckoning, not measured). So, it, too, should work in half-duplex.

So much to learn!
What do you think?  Thanks again for your help.

Hi,

according to NMEA0183 specs, one talker can speak to 4 listeners, so theoretically yes, you can wire the autohelm in parallel to your vhf. But you can have finer control over sentences when you have separate output to everyone.

I used the specs to have the GPS-mouse speak directly in parallel to the vhf and OP, so even if OP is not running for whatever reason, the vhf still has gps-data for distress calling...

with USB-RS422 converters just beware: I once had one (a cheap one) which gave interference on ch 16 of the vhf - and only on ch 16. Not good when you are boating. Took me some time to figure out, which element gave the noise on the vhf. 

just my 2cts

fair winds
Christian
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#5
Where is the gps nmea coming from in the first place? My garmin 128 sends nmea to the radio and pi, and radar. In to the Pi through usb/rs232 serial converter. They all just have data and ground, not data+/data- like newer devices. SH radio the same.

Sent from my SM-T813 using Tapatalk
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#6
(2019-05-26, 08:35 AM)PaddyB Wrote: Where is the gps nmea coming from in the first place? My garmin 128 sends nmea to the radio and pi, and radar. In to the Pi through usb/rs232 serial converter. They all just have data and ground, not data+/data- like newer devices. SH radio the same.

Sent from my SM-T813 using Tapatalk

Christian, I'd be interested to know if you physically modified your gps "mouse" to isolate it, or if you mean you configured OP to achieve it. I was thinking you meant you'd re-wired things, picked up a 12v to 5.5v converter, etc.

PaddyB, my gps source is a BU-353-S4 puck type usb A, powered from and plugged directly into the OP RPi.  It would take a separate power supply and a bit of hacking to make mine work independently from the Pi, but I can certainly see the advantages of that should the Pi go down. I guess I need a second gps puck and a small power converter if I want that data stream to be independent. The fellow in this youtube video demonstrates just how to do it, but with a PS-2 type gps: https://www.youtube.com/watch?v=2tG0RFKJQrs

On the other hand, if I leave the gps puck alone, I can easily transfer my one gps from the RPi to a laptop if the pi gets ill. I guess it's a trade off of capabilities.

Back to the matter of a shared RS425 line, after I get the vhf radio listening to the gps, on the same bus I'm going to try having OP create the NMEA sentences I'll need to drive the autohelm radio interface (Raymarine Z075). Somewhere in my searches I read that this device responds to XTR sentences, not XTE. If OpenCPN in tracking mode can be made to generate only XTE sentences, I might need to write a script to convert and transmit them as derived XTR sentences. (Of course, I'll give the XTE sentences a try first. I'm not a glutton for punishment!)

Thanks for the feedback, both of you!

Does anyone out there know anything about rewriting/modifying NMEA sentences as generated in OP or OCPN?
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#7
Ok. Just to confirm, the half-duplex dongle, (CH340T chip) RS422/RS425 usb A to mini-wire clamp posts worked just fine. 

(From Amazon, ~$7,  https://www.amazon.com/JBtek-Converter-A...27KYJ19G33 )

The RPi3B+ found it, and OP listed it in serial devices as /dev/ttyUSB0 , vendor 1a86, product 7523. I assigned it to Kplex with a unique name, running I/O= out, at 4800 baud. I identified the two NMEA wires in the accessory bundle of the Standard Horizon VHF, and connected them to the dongle. At first I had the polarity reversed, and nothing happened. I tried it the other way 'round, and, voila! The gps position appeared on the VHF screen.  The data moving through the dongle included an unfiltered mix of GP, AI, and AP sentences, and this did not seem to adversely affect the connection to the radio.

I had planned to try using the same dongle out to send autopilot instructions to  a Raymarine 'Radio Navigation Interface' (part Z075), but I've been unable to locate any substantial wiring information for the device. That's a subject for a different thread!

I hope these notes are helpful!
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#8
I'm also looking to send GPS data from my openplotter raspberry pi to VHF radio over NMEA 0183. My radio is a Navman 7110, with a 4-wire NMEA 0183 socket (IN+, IN-, OUT+, OUT-) operating at 4800baud. Could anyone point me in the right direction for the type of device to use? I'm a bit lost on the use of RS485/RS422. The out of the box USB to NMEA0183 solutions seem to vary from £50 to £150 Actisense converters which seem like complete overkill!
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#9
(2019-07-01, 02:03 PM)Melipone Wrote: I'm also looking to send GPS data from my openplotter raspberry pi to VHF radio over NMEA 0183. My radio is a Navman 7110, with a 4-wire NMEA 0183 socket (IN+, IN-, OUT+, OUT-) operating at 4800baud. Could anyone point me in the right direction for the type of device to use? I'm a bit lost on the use of  RS485/RS422. The out of the box USB to NMEA0183 solutions seem to vary from £50 to £150 Actisense converters which seem like complete overkill!
Hi. My post (just above yours in this thread) has a link to a usb dongle which worked for me.  This:
JBTek USB dongle


It's just two wires and can be configured to send the GPS nmea0183 to the In+/In- points on your vhf (I'm guessing those are right). It's inexpensive, and looks it, but works when configured in OpenPlotter. Good luck!


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#10
(2019-07-02, 12:18 AM)skyeyedoc Wrote:
(2019-07-01, 02:03 PM)Melipone Wrote: I'm also looking to send GPS data from my openplotter raspberry pi to VHF radio over NMEA 0183. My radio is a Navman 7110, with a 4-wire NMEA 0183 socket (IN+, IN-, OUT+, OUT-) operating at 4800baud. Could anyone point me in the right direction for the type of device to use? I'm a bit lost on the use of  RS485/RS422. The out of the box USB to NMEA0183 solutions seem to vary from £50 to £150 Actisense converters which seem like complete overkill!
Hi. My post (just above yours in this thread) has a link to a usb dongle which worked for me.  This:
JBTek USB dongle


It's just two wires and can be configured to send the GPS nmea0183 to the In+/In- points on your vhf (I'm guessing those are right). It's inexpensive, and looks it, but works when configured in OpenPlotter. Good luck!
 Thanks! I thought maybe as you only mentioned 2 wires I'd need something for 4, but I suppose the VHF doesn't need to send any data to the Pi. Will give it a try!
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