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

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djdan
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Hello!

I want to connect Leica RTK GPS (Leica SmartAntenna + Leica RX1250 controller) to LOWRANCE LMS-525 C DF via NMEA 0183. The reason for that is I want to get precise (centimeter level) position of sonar readings. Unfortunately there is some problem and I cannot diagnose it. I sticked to the manual when connecting everything, but without success. In the opposite direction (transmitting position of sonar from standard Lowrance GPS) NMEA 0183 works fine and I can read GGA message on PC (via Parani bluetooth serial adapters and then in Python script).

This is the NMEA GGA message received from Leica GPS:
b'$GPGGA,203748.40,4925.8006561,N,02016.5010872,E,1,05,4.0,653.042,M,,,,*3C\r\n'

And this is the NMEA GGA message received from standard Lowrance GPS:
b'$GPGGA,203557,4925.8007,N,02016.5573,E,1,3,4.41,-41,M,,,,*17\r\n'

 

So they only differ in position decimal precision. I’ve also tried to transmit this Lowrance GPS NMEA GGA back to the sonar – without succes :/ 

 

I’ve tried to show everything on the video:

Here are also some useful pictures: https://drive.google.com/drive/folders/1SzBnptYiXg3HtKRgPSlmPxXXSCqDRiiO?usp=sharing

Link to Sonar manual found on the internet:

 

I will be very grateful for any suggestion and help!

Thank you!

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Richard Imrie
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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. 

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Richard Imrie
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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.

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djdan
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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? 

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Richard Imrie
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@djdan

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

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

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

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 😉 

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Richard Imrie
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@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.

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djdan
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@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. 

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 😀 

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Richard Imrie
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@djdan

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

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djdan
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@richard-imrie

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

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djdan
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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?

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