Brian Chamberlain
Software Engineer & Electronics Nerd

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OpenWater V2

DIY swimming-pool-ready remote water quality monitoring


This project is also featured on Hackster.io

Background

For even more background see version 1 here

In this version I threw out the enclosure and the PCB design of the first version. I wanted a device that looked half-way decent. The cable situation in V1 was also really not in a good place.

I thought that one interesting idea might be to create an inflatable enclosure. It could potentially mean that a majority of the enclosure could be made from cheap rubber inner-tube. Adding air pressure would:

  1. Still be soft if someone were to cannon-ball onto it while it's floating in the pool
  2. Keep the cost down
  3. Be an easily sourced material
  4. You would know right away if there was a hole that could allow water to leak-in, air would leak out

What I learned was I was wrong about any of these being a real benefit.

  1. While soft yes, I still needed rigid end-caps and exposed hose clamps. Those are not super friendly to the accidental errant (or intentional) dunking.
  2. I found it difficult to find the diameter of tubing that had the right flexibility and durability. I ended up finding a supplier of industrial roller covers (for use in printing). At $45 per/foot, it was not the most economical.
  3. Nope, see #2 above. Required special order from specialty manufacturing. See Jemmco for a great source for extrusion and web converting industrial supply!

Also, one big learning was that I never calculated the buoyancy of my device. It turns out that even with the entire enclosure totally deflated there was not enough mass to pull it down and have it float the way I had intended. I would need to add about a pound or more of ballast to the bottom to get it to float. Even then, it did not float up/down but instead kind of listed to one side like some half-dead fish.

Block Diagram

Component Diagram

3D designed/Printed components

Enclosure top cap

Enclosure bottom cap

Materials

Here's a materials list in gDrive. See the tabs at the bottom, select V2.

https://docs.google.com/spreadsheets/d/1hH_PX7qE9Eqqa5zU-xhwlhM-gbqpwk3e61Kn0q8U03g/edit?usp=sharing

These are all the parts needed openwater v2 pcb parts

This is the sensor array and battery mounted to the base. The USB cables mounted and sealed in the cap. openwater v2 parts

Back of the PCB after assembly openwater v2 pcb assembled openwater v2 pcb assembled back

Here is a test-fit of the PCB in the 3D printed cap. I designed the lid with a board slot and pull tabs that snap into place over the holes in the PCB. Fits perfectly. Digital manufacturing is amazing. openwater v2 pcb fitted openwater v2 board mount cap

openwater v2 usb charger port openwater v2 inflator mounted

The batteries and probes mounted and ready. openwater v2 batteries packed

Sealed up the enclosure with a pipe clamp openwater v2 sealed up

openwater v2 inflate ready It inflates! It holds pressure really well. openwater v2 inflated

I was a little concerned about the silicone barge cement I used to glue the bottom holding up against the pressure so (for now) added some zip ties. openwater v2 inflation restraints

Inflated the project was much too bouyant. This is what I get for not doing any calculations beforehand. openwater v2 buoyancy test

Even when deflated it's still too bouyant. I used the loop I desigend into the 3D printed probe mount to attach a weight. It worked to keep the device submerged so I could do some further testing. openwater v2 deflated buoyancy test

What I found out was that if there is no internal pressure keeping the bike-tube inflator valve sealed it leakes. After a day of sitting in the bucket submerged the entire enclosure filled with water! Luckily nothing was damaged. I thought for sure the battery would be toast but it's still totally functional. Anker designed a great product there!

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