I'm currently working on a irrigation system for which I would like to build a low cost soil moisture sensor. I would like to measure the moisture levels of a given environment based on a capacitance.
So far I was unable to find a differential capacitance sensor (see fig.I)
I had a look at multiple touch sensors controller/button controller/you name it. They all had a ground plane and did not measure in differential mode. Does anybody know a differential capacitance sensor suitable for my purposes.
Note: Due to volume restrictions in my design, I am unable to use a sensor with a ground plane per measurement plane. Also, due to flexibility in the design (see fig. II) I can adjust the copper tube to match the capacity range of the sensor and can therefor not specify such a range.
Note 2: The copper tube inside the plastic tube should function as measurement pads. (see fig. II)