Question: DIY conductivity Sensors

roberts_ecofarm asked on October 24, 2018 01:58
75 | 1 answers | #17365

I'm working with a CitSci group in Eastern OH trying to develop a water quality sensor network to monitor changes in TDS in peoples well water and in local springs. We are the new dumping ground for the waste brine from fracking in PA and OH. Massive amounts being pumped into injection wells in our area so we are trying to get ahead of the curve on monitoring change. Need to keep the cost of the sensor/logger package under $20 as we are working with a very small budget. Planning to use the promini logger from the Cave Pearl Project as Ed seems to have worked out all the issues with that brilliantly. I've seen some threads here for different sensors but they seem to stop a couple of years ago. Anyone still working on this problem, or have any guidance for development of a low cost option?


You are right that there has not been much follow-through at Public Lab on developing and testing DIY conductivity or total dissolved solids (TDS) sensors. Part of the reason for that is the difficulty of making a reliable sensor. Calibrating the sensor and getting it to provide consistent results for more than a few days under water are serious challenges. A good attempt is here, but there is not much info about successful deployments.

Your goal of making a data logger with TDS sensor for $20.00 is ambitious. You can buy the basic parts for a Cave Pearl Logger or Mini Pearl Logger for about $10 if you order everything from sellers in Asia. You can probably make a TDS sensor from basic parts for another $10, but some of the challenges (low voltage, alternating current) might require a complex design and careful sourcing of components.

I have tried the DFRobot TDS sensor with a Mini Pearl Logger and it seems to have potential. I have only tried it in a spring house and I think the water there is so clean that most or all of the variation in the TDS results is noise. More testing is needed. That sensor costs $13.00 which is a very good deal considering that it apparently has both the low voltage and alternating current features.

Ed Mallon's focus with the Cave Pearl Loggers has been to get them to last more than a year on small batteries. This requires intricate modification of off-the-shelf components and complex code to sleep the components between logging events. The Mini Pearl Logger uses a different approach to longevity and uses an external low-voltage timer to turn the data logger off between logging events. It is much simpler to build and program. There has not been enough time to determine if this provides comparable longevity. Do you need longevity?

Are you going to deploy the loggers in drilled wells or test the tap water? If the latter, maybe you don't need a data logger and a hand-held TDS meter would be sufficient. That is even easier to build from an Arduino Pro Mini, and does not involve the heartbreak of multi-week deployments of faulty loggers. But maybe your plan is to monitor the live data via radio so faulty loggers will be identified. That will be even harder to do for $20 per logger, although maybe not impossible.


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Thanks Chris,

We have multiple injection well sites in our county, and more in the works, so we are planning on covering a large area. We will be installing sensors at drinking water wellheads and in some springs and creeks. I've used the Cave Pearl Logger in a tensiometer project I'm developing, and like how it has held up in the field. For this project I'd like to have the option for data storage on an sd card as well as developing an up-link option where feasible. Total package will probably exceed my $20 budget, but I'd really like to keep the logger-sensor component under that if possible.

I'm still pulling together some ideas and making a plan for the sensor part. I'll post it as a project when I have it a little better defined.

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Hi! The simplest (and cheapest) conductivity sensor I can think of is the Coqui-- we have a recent blog post about it here, and I would imagine with some tinkering it could be used with a logger, but as Chris suggests, if you're planning to use something on site, you may not need this part. @kanarinka is one of the people behind the Coqui, perhaps she's got some suggestions?

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