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Let talk about Serial Connections
#1
I have been trying to connect my old Garmin Plotter to my pi via NMEA0183-RS422-USB.  the RS422-USB device is:

https://www.amazon.com/gp/product/B076WVFXN8

at first it had me scratching my head because TX+ to RX+ and TX- to RX- did not work but connecting TX+ to RX- and TX- to RX+ worked, and so I also connected RX- to TX+ and now I have lights - Red for Power, Amber for RX and then after selecting "depth under transducer" in the signalk to NMEA0183 plugin - Green for TX - and I got a notification on the Garmin that the depth was shallow (I am out of the water!)

what I am not seeing is any data in Signalk.  I played around a little with the options:
   
but could not see any entries in Signalk

Any ideas?
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#2
You may need to connect TX+ to RX+ and TX- to RX-. Not sure on that, as it's been such a long time since I've wired anything NMEA0183, but I think "polarity" matters, but I'm not positive.

Crap, I just wrote this long post and deleted it in a edit!

Well, here's recap in a nutshell:

I assume you added drivers for your USB device. You added the device into OP_Serial, gave it an alias, and added it to SignalK.

In SignalK, you edited the connection and verified it's set to "Serial", the port is set to the OP_Serial Alias, the baud rate is correct, and output events is set to "nmea0183out".

Save your changes and reboot SK. Then check the data browser, you should see SK Paths begin to propagate SK sentences.

Is your depth sounder connected to the Garmin? If not, turning on the plugin may be generating a "0" value and sending it back to the Garmin, which you don't want, as that can create a loop. Serial connections are by-directional, so this is something to watch out for. If your depth sounder is connected to the Garmin, then it may very well be sending those sentences, so there's no need to send them back.

Usually, each NMEA018 device needs its own serial connection, unless there's a multiplexer-type device somewhere. The Garmin may act in that sense.

Steve
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#3
the Depth transducer is Seatalk1 and is going into signalK via a ST1 to Pi GPIO optocoupler. then the DBT sentence has been selected to be forwarded via the SignalK to NMEA0183 plugin. So from that the outgoing connection is working, therefore baudrate and outbound serial connection is working - the incoming connection is on the same page so there are only a few variables to play with. I am not at the boat but will screen shot it next time I am
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#4
(2021-04-15, 02:35 AM)Techstyle Wrote: the Depth transducer is Seatalk1 and is going into signalK via a ST1 to Pi GPIO optocoupler.  then the DBT sentence has been selected to be forwarded via the SignalK to NMEA0183 plugin.  So from that the outgoing connection is working, therefore baudrate and outbound serial connection is working - the incoming connection is on the same page so there are only a few variables to play with.  I am not at the boat but will screen shot it next time I am

Oh awesome! So you do have it working! When you get back to the boat, check the Garmin settings and make sure it's sending nmea0183 data. I'm not familiar with Garmin, but I'd guess there's a setting in the unit to "turn on" the connection.
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