Public Lab Research note

sensors in soda bottles

by mathew | February 26, 2015 03:45 26 Feb 03:45 | #11640 | #11640

mathew was awarded the Basic Barnstar by warren for their work in this research note.

What I want to do

I want to keep electronics dry while wired to underwater sensors. I did a short test of a simple system of caulk filled tubes stuck through rubber stoppers in the tops of pop bottles. I did a test submerging it half a meter (18") down in a trashcan full of water.



My attempt and results

New additions to the design:

  • I used clear plastic tubing instead of brass tubing (3/8" OD (outside diameter) PET tubing)
  • I ran wires down the length of the tube before filling with silicone caulk to simulate running sensors
  • I filled the bottles with rice both to act as a desiccant (pulling moisture out of the air) and because it makes the bottle less compressible and I think will help maintain shape at depth. Also, rice sticks to moisture and I can use that to tell whether the bottles leaked.


I could fit four wires off a 0.1" ribbon cable through the tube.

Throwing it in the River

I threw it in and dragged it out three times just to be extra rough, then I tossed them about four feet (120cm) down.


I threw it in the water on the 16th of february and just picked it up at almost low-tide on the 25th (at 5:40pm). It was submerged under about 5' (150cm) of water at least some of last week.

NOAA Willamette River water levels:


here they are tied up at low tide when I retrieved them. ; IMG_20150225_170657.jpg

Questions and next steps

Go deeper-- attach real electronics and sensors.

Why I'm interested

$1 waterproofing

I did this Help out by offering feedback!

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Have you tried using heat shrink wrap yet as a sealant?

Electrical tape also works as shrink wrap - just apply some stream/heat to it and it tightens up.

Great for making seals on wine bottle...etc...

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i've tried heat shrink tubing in other projects-- I don't find that it provides a perfect seal and it has difficulty sticking to glues since its usually a polyolyfin material. it is very useful at reducing the stress on a wire around a waterproofing joint though.

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That's a great idea to use rice to make the bottle non-compressible. It can also keep your payload dry if a little water leaks in. For the testing phase, unless you weigh the rice (very carefully) before and after, how do know whether a little bit of water leaked in?

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Not sure if this would be an option but Self-fusing Silicone Tape works very well for sealing even in wet and underwater conditions.

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@cfastie I guess I can't guarantee they didn't leak a bit, but in my experience the rice sticks to the side of the bottle if there is moisture. I'm not sure if that applies after the water has been sitting in the rice for a week.

@Nashblackcat I'll take a look at the silicone tape. The silicone sealant is messy and I wonder if I can use the tape as packing around the wires.

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Mat: It is great for insulation! ASAS has it cheap so you can try it out and not break the bank.

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