Power Sensor Using GPIO - BitKnitting/should_I_water GitHub Wiki

Awhile back, I read Chris Ruppel's blog post - Arduino Soil Moisture Sensor. In the post, Chris notes: ... the docs for this sensor (PDF, 98KB) recommend that you only send power to the sensor when actively taking a reading of the soil moisture. Powering only during these short moments helps avoid corrosion caused by the constant flow of electricity between the two pads of the sensor.

The sensor I am using is similar to Sparkfun's sensor. I get different readings when I use the 3.3V pin than the GPIO (~400 vs. ~200). I don't understand this. However, I went back to using a GPIO pin to power the sensor as Chris's blog post advises to do.