Originally Posted by jurek
My goal is to connect Garmin GSD 26 Sounder with laptop and use laptop to listen and control this device. I prepared Garmin Marine
Network -> RS232 -> USB interface and download Advanced NMEA Data Logger and Advanced Serial Data Logger, but I am not able to listen and control my device.
Disclaimer: I really don't know anything about Garmin's Marine Network, but as no-one with more knowledge has replied I think I can take a guess at some of the (several) things that might be wrong with this picture.
I think the issue is that you are expecting the network to carry serial data in an NMEA-0180/NMEA-0182 (or NMEA-0183) format as indicated by your "NMEA to RS232" diagram and choice of data logger software
. I don't believe that this is the case. exposure stated in post #2 that it was ethernet at the lower protocol layers. At higher layers the data will be encapsulated in a non-public proprietary format. It might be that data other than sonar imaging data is carried in an nmea-style format *within* that encapsulation (perhaps a Garmin expert here could tell us?) but my guess would be that that would be more likely to look like NMEA-2000 than NMEA-0183.
The first problem here then may be assuming that the wire carries serial data. Whilst RJ45s are used for serial connections to, for example, console ports
of some servers, routers and switches, your wires here are not used for serial data: it's ethernet so you can't wire it to a DB9 and read it like an RS232 connection.
The data format I already mentioned: almost certainly not what you are expecting to read.
Someone else here may have a better plan but presumably you have your sonar connected to a Garmin MFD (plotter or whatever you call it) to display the imaging data. If so check the manual to see if it does data bridging and has an nmea-0183 output. If so, leave the sonar connected to the MFD and take the data feed from the nmea-0183 output to the laptop. You obviously won't get imaging data, but it might do depth
(and other sources might give you position).
About that "NMEA to RS232" circuit though...lose that. I'm no electronics
expert but that looks to be converting between TTL and RS232 which may be from pre-NMEA-0183 times (even before the first -0183 iteration which would have been happy with RS232). More recent NMEA-0183 iterations will be opto-isolated and be putting out (differential) rs422.