Hydrographic/ bathymetric survey: Lowrance LMS-525 C DF receiving NMEA 0183 problem (from Leica GPS 1200 RTK)

We have a similar setup but the sounder (Lowrance HDS) sends Depth to the RTK data collector (DC) via Bluetooth.

Somewhere there needs to be a "null-modem", which can be achieved by changing the RX/TX pins on one side of the data link - you possibly don't have this on the DC-sonar setup.

On our Lowrance system, a yellow wire generally represents a "wake-up" wire, such that when connected, starting one instrument will trigger start up of another.

For the Privateer, these things are tricky but seeing as you have the data going to the PC, you must be very close - don't give up.?ÿ

Also, check which sentence the sonar accepts for GPS position. I think there are at least a couple of different "versions" of position - just like for sonar depth, there are at least a couple of versions of depth.

Thank you for suggestion! 😀 I didn't try to send the depth to the controller. I'll try and let you know if anything came out of it.

Null modem is already connected to the serial cable going from DC.

What Data Collector do you have??ÿ

Ok, sending depth from sonar to the Leica Data Collector works! 😀 It's a pity, that it's sending it only in 1Hz rate :/?ÿ

Thank you @Richard-Imrie so much for this suggestion! :D?ÿ

But if someone would guide me how to transmit Leica GPS data to sonar, I will be also very grateful. Leica can measure in 20Hz rate, so it would be huuuuge improvement ;)?ÿ

Posted by: @djdan

Ok, sending depth from sonar to the Leica Data Collector works! It's a pity, that it's sending it only in 1Hz rate :/?ÿ

Thank you @Richard-Imrie so much for this suggestion! ?ÿ

But if someone would guide me how to transmit Leica GPS data to sonar, I will be also very grateful. Leica can measure in 20Hz rate, so it would be huuuuge improvement ?ÿ

Are you really needing to log at 20Hz?

Considering the variation in the orientation of the transducer that inevitably occurs while measuring hydro data, plus the fact that the single-beam precision will vary with depth, it seems like overkill. Unless you're logging data from an IMU at the same time, 20Hz is just going to give you a ton of overlapping measurements that will look impressive but in reality won't be any better than if you logged at a slower rate.

For single-beam applications, I don't think I have ever recorded faster than 1Hz, and even then I usually cull measurements when creating deliverables.?ÿ

You are right, that 20Hz in this case is an exaggeration, but higher recording rate would make it possible to average measurements from i.e. every half of second, which would lead to better overall measurement quality. I think so ?????ÿ

@djdan

Maybe therein is the issue: 20Hz RTK to sonar "overloads" the sonar.

Also, on our Lowrance HDS (which is a bit more modern than your unit), there is another system page where you get to select the GNSS source - maybe there is something similar on your unit.

As I understand it, consumer grade sonars were always 1Hz pings - if you put the transducer in a bucket you can hear it clicking (survey grade sonars often had a higher rate). But that may have changed with the modern technology, as our Lowrance HDS does not specify the ping rate, but does have a "slider" that you can change from low to high, and everywhere in between - we leave it on high.

One other thing I've found out (the hard way) is to limit the data transmission to only the NMEA sentence(s) that are required - I presume it's the bandwidth that can be overloaded with extra data and that can stop things working.

@richard-imrie

I've tried to limit RTK to 1Hz and through NMEA transmit only GGA message. I've tried also to change baud rate (I checked the values from 4800 to 115400). Nothing from this seems to work. Unfortunately on my unit this is only page, where I can manipulate NMEA/GPS source.?ÿ

My sonar is pretty fast - clicks are about 10Hz on 50% "Ping Speed". Hard to count, but it nearly overlap with 600BPM music metronome. Anyway it's much much faster than 1Hz. On 100% "Ping Speed" slider it's like machine gun mounted on the helicopter :D?ÿ

@djdan

Sounds good. Getting back to the Leica-sonar configuration, have you tried taking out the null modem - mysterious things can happen?

@djdan

Our DC runs SurvCE, which has a tab for peripheral equipment:

@richard-imrie

Null modem must be there, because it's between 2 female DB9 connectors

I think the problem is inside sonar - this circuit closing, which I showed at the end of the video worries me. But I'm not an electronics engineer and becasue it is working in 1Hz mode I'm not sure if it's worth to rummage inside it. What do you think?

I personally wouldn't fiddle inside the sonar, my experience is that there's nothing inside that a Privateer can change.

I would still however trying it without a null modem, or try changing the TX/RX pins on one side.

@richard-imrie

Tried to changing TX/RX pins - nothing happen :/?ÿ

Ok. Have you checked whether in the Leica-sonar direct cable configuration, they need to share (or not share) a common ground?