Acoustic Monitoring Buoy

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Some data and some challenges!
Julian Blanco • 11/25/2023 at 22:19 • 0 comments

Hi all,

Just a quick update since I was able to gather some initial data.
I made the mistake of grounding the hydrophone ground to frame ground (and effectively seawater). This caused some low frequency stability issues in the pre-amp since it was not expecting the input to be grounded and ended up saturating the ADC (at least this is my working theory).

I am planning on deploying again soon but in the mean time here is some data!

The vertical stripes in the spectrogram are spots where the waveform clipped which is easier to see / understand in the waveform view.

If you are wondering what the concave up curve is in the spectrogram, it is the doppler shift of a boat passing the recorder!
Sensor interfacing
Julian Blanco • 09/05/2023 at 04:22 • 0 comments

In order to talk to the blue robotics sensors, i needed to connect to them via I2C. The connectors use JST-GH connnectors but I wanted to connect it to the QWIIC port on my microcontroller so I made a little interface board to connect the two.
Making waterproof connections at depth
Julian Blanco • 09/05/2023 at 04:01 • 0 comments

One of the learning curves I had to get up to speed on was making waterproof electrical connections at depth. There are two ways that I found helpful to doing this.
Bulkheads and penetrators.

Bulkheads are (usually) female connectors with some type of sealing gasket that allow a male plug to attach and mate.
Penetrators are generally wires which get fed through a physical passthrough and potted with epoxy to make them waterproof.
I am trying both on this project.

First I tried to make some penetrators, I resin printed some penetrators from a CAD file i found online.
Cleaned up the threads with a tap and die set and then potted my cable.

Most professionals use Loctite DP420 for potting, but I choose to use a suitable knock off of Infinity Bond EP420 which is much cheaper at 16$ for 50ml and has similar properties.
I kinda doubt that this is going to work at really deep depths but hopefully they hold up for a hundred feet or so underwater.
As a secondary that I know will work, I like using bulkheads from Blue Trail Engineering. They are relatively inexpensive for bulkheads and are really nice.
Single Pair Ethernet Setup
Julian Blanco • 08/31/2023 at 15:47 • 0 comments

In order to communicate with the acoustic bottle at depth, my communication method needed to be able to communicate over long distance. RS-232 tops out at ~50feet/15meters and serial wasn't probably the right choice here longterm. Blue robotics sells a tether interface that runs over Homeplug-AV (IEEE-1901) which is good for 300meters, but the Sparkfun Single Pair Ethernet kit seemed really cool and the fact the ADIN1110 chip used in the product is spec'd to consume 50mW at full 10mbps was a huge bonus for a potentially battery powered setup.

Eventually I would like to try and connect two bottles underwater at the full spec of 1700m of the SPE pair but for now, connecting the bottom payload to the surface bouy with 100m of cable was plenty.

The 1 foot cable that came with the kit was great for testing, but first thing i did was order the parts I need to make my own cable.

Mouser:

Plug: 617-09451812810XL

Crimp: 617-09455002810

Quick and dirty for now, but I wanted to make sure it worked for now! Eventually I plan to pot the cable in a Cobalt connector from Blue Trail Engineering since those are my favorite low cost waterproof connectors (600meter under!)

For some reason in my head i was worried if the if you had to do tx->rx cross like UARTs but turns out the wiring can be reversed and it still works!

With my cable now tested, I can move on to writing a proof of concept driver.

Eventually I would like to run PPP serial link over the connection but for now, i will settle with getting short messages across.

My arduino code's goal would be:

Sample the USB serial UART and buffer any bytes present

Pack a frame and send over the SPE connection if a byte is present in the circular buffer

Ive posted my code here.

And success! Hello world!\n was successfully sent!

Now, the acoustic monitoring payload can send strings over the tether up to the surface about what it is hearing. Hopefully, i can use the full speed of the ADS1110 eventually to transfer raw audio up too!