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
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