I recently bought a moisture sensor off eBay (one of those Chinese YL-69 like can be seen here) and my original plan was to use it with an Arduino board. However, after much experimenting I realize there is a chance my sensor was broken, so before I go back to eBay to complain, I would very much appreciate expert advice.
Because the readouts were so wonky, I decided to perform the simplest test: plug the YL-69 to the also included YL-38 (as can be seen here), power the YL-38 (it has on one side VCC, GND, D0 and A0 and on the other side two input pins to plug to the YL-69) and this YL-38 lights up a blue LED just by having current flowing through it. Additionally, depending on the resistance applied on the two IN pins and depending on the potentiometer's adjustment, it will light up a red LED once the resistance to the IN pins crosses the threshold defined by the potentiometer.
From what I was able to read online, normally, by sticking the YL-69 on water, it should cause the resistance at the IN pins to be almost nil and thus the red LED would stay lit for as long as this is happening. However, what happens is that as soon as I stick the YL-69 in water (not completely obviously), the red LED comes up for a while (indicating that the water had an effect in lowering resistance) but after just 2 or 3 seconds it turns back off.
This is consistent to when I was reading the A0 values with the Arduino. I was getting what I sometimes thought was the right reading but it would always level out back to 300-ish.
My question is: is my YL-69 sensor broken? Thanks in advance!