April 11, 2013 AT 8:01 am

DIY Soil Moisture Sensor

Michael Ciuffo built this neat soil moisture sensor for his girlfriend, since she’s had some bad luck with plants. He writes:

In the June 2012 issue of Nuts & Volts, they did a spread about making a soil moisture sensor with an iPhone interface:

And when I heard my girlfriend say that she has trouble remembering to water her plants, I put two and two together.

Most of the N&V article discussed the code required to interface with the iPhone, but the important part for me was that their soil moisture sensor was nothing more than a simple conductivity sensor. The more water in the soil, the lower its resistance.

Such a sensor doesn’t measure soil moisture in any kind of universal unit, but for a single sensor in a particular soil sample, the measured conductivity is repeatable and proportional to the moisture level. I call these conductivity units “AMU”s or “Arbitrary Moisture Units”.

Neat project and nice build!

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