Depth sensor with SD card for robot-boat

Hi, I am looking to build a simple drone boat for bathymetry measurements of a small lake. I am inspired by Randy MacKay’s drone boat based on a boogie board for a hull.

Initially, I would like to start experimenting with just a depth sensor, GPS, and writing output of location+depth on an SD card. I will first do tests by towing the platform with my kayak. But as I am looking at the Reference Frames docs, I can’t figure out the parts I need. Several years ago I built something similar with a Garmin depth thru hall sensor, an APM 2.5, and an Adfruit Ultimate GPS Logger Shield but these are now obsolete technologies.

Specifically, I don’t quite get what I need to connect and be able to write the GPS location of each depth measurement to the SD card. Would a PX4 do the trick for all components or do I need additional parts?

What would be the minimal hardware mix I would need for now (assuming without mobility parts such as thrusters, motors, and any remote control or autonomy) just to tow and record?

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Welcome @GeorgeD,

You’ve probably already seen it but here’s the reference frame page for the boogie board boat.

If the echo sounder is directly connected to the autopilot as a “range finder” then DPTH messages will be stored to the onboard log and they can be extracted later and then imported to ReefMaster (or similar).

If you’ve still got the Garmin depth sensor it may be possible to use it although it depends upon what output it provides. E.g. if it’s NMEA 0183 then it can probably be connected like the Echologger ECT400 but this is probably not the case actually.

Thank you @rmackay9!

Yes, the sounder was a Garmin Intelliducer (NMEA 0183) and used ReefMaster for data extraction. Unfortunately, the ECT400 price point is above my budget. As I am looking for the most straightforward solution, from the available sounders, does the BlueRobotics Ping sounder sound (…pun intended) the simplest option for integration?

I am thinking of a PX4+BlueRobotics Ping+GPS/Compass+SD+battery on a boogie board being towed to start with and ReefMaster or Python scripts to extract data – would this do the trick?

@GeorgeD,

That sounds like a good setup to me.

So just to be clear, if you still have the Garmin Intelliducer it can probably be used because AP has a NMEA 0183 rangefinder driver (used for the ECT400).

I suspect the Ping or the Kogger will work OK. I have both but sadly I haven’t actually tested either yet.

Just a terminology thing, when you say “PX4” you probably mean “Pixhawk”? In any case AP supports a huge number of different autopilots.

@rmackay9, yes I still have the Garmin and will give it a try first. Last I checked it was behaving erratically (suspecting wire corrosion) so I may have to resort to the Ping as Kogger seems to be on backorder.

Thank you, I was misusing “PX4” – referring to and looking at a Cube Orange + Here3 Combo (Pixhawk Orange & ADS-B Carrier Board). This tech stack should work for bathymetry and I can build on it to add later thrusters and RC…

I will report back once I have an assembled and working platform. Thank you!

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When you say “like the Echologger” do you mean that a device like the SprkfunFun RS232 Shifter is needed? I have a Lowrance Elite T2 that has both NMEA 0183 and NMEA 2000 outputs. Would a RS232 To Serial converter still be needed? Or can I connect directly to TELEM 2, and if so what are the connections?

Like others, I have built a boat and use the Cube Orange as an Auto Pilot with Mission Planner and was hoping to get realtime Depth. The Wifi to smart phone is very limited on the Lowrance Elite T2 and I typically am outside the Wifi range on long missions. The RFDesign 900x Telemetry works great for the long haul and would like to pick up depth at the same time.

Thanks for the help.