(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.
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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?