I added a couple of capacitive soil sensors and have always had a problem with them and decided to finally sort it out.
ADS1015 ADC 12bit
Resistive photocell with Pot
Two capacitive soil sensors
At the moment when the light changes so do the values of both soils sensors. The soil sensor values do not change much if the soil is wet or dry - I am now wondering if it is changing but the changes are so small compared to the troughs I calibrated them to?
Relavant part of the circuit diagram
I have a small diode on the input to VDD