Background

A friend of mine is working on a startup in SF building a water quality monitoring device aimed at the pool/spa market. They have a lot of interest in their product, especially from NGOs looking to use it in developing countries. His team had started this open source water monitoring device but didn't have much time to work on it. I'm a big fan of my friend's idea and company—I think it has a lot of potential to do good. I offered to help. It sounded like a great challenge.

Project Goals

• Build a water quality measuring system that uses off-the-shelf enclosure components at low cost
• Use the Atlas Scientific pH, ORP, and Temperature probes and sensor modules
• Last for at least a month without swapping or charging the battery
• Based on Particle Photon for WiFi backhaul
• "Easy" to assemble—I was trying to design a project that at most only required some light soldering. No cutting, no drilling, no specialized equipment, minimal if any adhesives, etc.

Things I Learned

While the enclosure only cost about $20 in total (the pool floater + blender bottle), getting it to hold the component cables and be watertight was not possible. I could have epoxied the crap out of the cable port to seal it, but then I wouldn't be able to swap out the sensors if I needed to.

If you consider that the electronics all-in cost over $400 USD, you're actually probably okay with spending $100 or more on an enclosure that will stand up to the challenges of the pool/spa environment. A cheap enclosure that leaks and ruins the electronics isn't any kind of savings.

Really, the cable management situation was the biggest takeaway. The probe manufacturers give you several feet of lead between the sensor and the BNC terminator. I could have cut the cable down, but I was really trying not to alter the sensor probes in any way. They're quite sensitive, and as it says on the Atlas Scientific site... if you cut the cable you void any warranty.

Materials

Here's a materials list in Google Drive. See the tabs at the bottom and select V1.

Assembly

Custom PCBs to hold each of the sensor boards. The original idea (why the boards look like they do) was to pair a Photon per sensor—this way you could build one sensor type at a time. Each sensor would be stand-alone so you could put them in different spots in the pool. I abandoned this idea when I started looking at enclosure options.

Rough-in of components. They all fit! Things were looking pretty promising at the time.

Assembled, I guess. It technically floats (when I added about 1.5 lbs of lead shot to the bottom). At least getting to this point got me to iterate on the software side a bit.