Looking at the principles of operation of the Capacitive soil moisture sensor, testing its output in wet to dry conditions, and taking it out to the garden for a real soil test!

These sensors on Amazon (affiliate links):
Amazon.com: https://amzn.to/2LJ6kLS
Amazon.ca: https://amzn.to/2JnQDrV

Capacitive Sensor References:
CapacitiveBased Liquid Level Sensing Sensor Reference
Design
http://www.ti.com/lit/ug/tidu736a/tid...

The FringeCapacitance of Etching Holes for CMOSMEMS
http://www.mdpi.com/2072666X/6/11/14...

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