I've been having trouble with some capacitive soil moisture sensors, and I'm hoping to find some answers here.
The one I am using is like this: https://i.imgur.com/tLj1zax.png
Basically, by default analogRead gives a very low value (10-20). If I put it in water, it does not change at all. Yet if I touch it with my finger, the value skyrockets to 500-600. If I put it in water, then dip my finger in the water, once again its value increases. Not because of the water, but because of my finger.
I have 4 of these sensors, so I tried it with a second sensor, and had the exact same result.
I connect it to a nodemcu v3 with a very straightforward setup - vcc to 3v, gnd to gnd, data to A0. No voltage dividers or pullup / pulldown resistors. Do I need one? None of the examples I have seen mentioned one.
One thing I noticed is that my sensors are a little different from the one I see in many tutorials; notice the part in the U2 location on this sensor:
I believe that is a voltage regulator? My version just has a resistor between two pins, and the third pin is empty. (As you can see in the first image). Does that mean anything? From my rudimentary knowledge I'm guessing it means that the sensor only runs on 3.3v? Or maybe it only runs on 5v?
I'm really scratching my head here. I found a topic on these forums from a couple months ago with some people having the same problem, but no solutions.
I hope that I can figure out what is wrong with your help!