Repurposing Captured Sounder Buoys


I’m a PhD student in Hawai’i and I have been tinkering with arduino for awhile now - mostly building data loggers modified from Edward Mallon’s designs via the Cave Pearl Project.

Today I was given a captured sounder buoy, it’s an M3i from Marine Instruments. Long story short these things are attached to illegal fish attracting devices (FADs) and they report back to the ship the biomass of tuna beneath the FAD using a 50/200 kHz echosounder.

Now that I have this thing, I’d like to repurpose it to do some good in the world. From what I can tell it uses the company’s proprietary software, but I’m hoping to find a wiring diagram and patch in somehow. Worse case, I’m hoping to scrap the board but reuse components and turn it into my own monitoring buoy.

Components I can see right off the bat:

  • Ublox GPS module
  • 50/200 kHz echosounder
  • Water temperature sensor
  • Iridium satellite module (I don’t plan on using it, data plans are too expensive). I’ll probably go cellular or wireless mesh.
  • Fancy solar panels
  • Giant battery pack

My Question: Assuming I cannot find a copy of the company’s closely-guarded software, any suggestions on how I might interface with the components short of stripping them off the board? I’d like to patch in directly to the board with an arduino if at all possible - hoping there is a testing/QC port open.

Quite a nice gift!

I'm hoping to find a wiring diagram

That is at least as unlikely as deciphering the "closely-guarded software", although it may be possible to reverse engineer the motherboard. Probably not a simple task, but post some photos!

It should not be too hard to remove and reuse some of the modules.

Iridium data plans are [u]cheap[/u], for a few bytes sent now and then, and work where there are no cell phone towers, which happens to include most of the ocean.

If this is something you can get more of you might consider sending it off to one of the reverse engineering/teardown YouTubers. There is a good story behind it so it seems like the sort of thing one of them would be interested in.

Attaching photos now. Lots of interesting components! If anyone feels like helping out with a partial wiring diagram it’d be great. Otherwise I think I’m going to take the approach of stripping and reusing components.

Question: I’ve been reading up on the RockBlock Iridium SBD module. Is there a way for me to interface directly via arduino with the stock iridium module in the buoy, or do I need to source an empty RockBlock and incorporate the salvaged module?

For security I’ve blocked out all serial numbers.


Iridium models are easy to use with Arduino. It is just a TTL level serial connection. Google “gortobot” for an example of one on an autonomous sailboat project.

I would not attempt to reverse engineer that complex board!

If you told us that it powers up, I missed it!


It would be pretty cool if you could somehow use the satellite link to send the poachers phony information!

If the buoy powers up, monitor what goes into the Irridium module (and what comes out, if anything). An Arduino should have no problem with that, but be sure to scope out the serial communications voltage levels and Baud rate before making any connections.