Built automatic irregation system for outdoor plastic pots. first tried soil sensor with capacitance - was extremely unrelyable, sensed moisture outside pot, and other unknown factors changed readings about 3 times more than the actual soil moisture I was trying to measure. (Used absolute results)
http://pcb.daince.net/doku.php?id=ebay_soil_hum_temp_aio_v100 (it actually worked very well in short tests)
Now stripped insulation and tried with simple analog readings with resistor. with the same plate. This works much better but still horrible. there are 4 zones in different depths , moisture is sum of them, in the time there have been readins there has been no rain, so it should have been very stable slightly going down. "target" is a potentiometer wich hasn't been touched, and it's also not stable in readings.
using 12v power for arduino because I use the same power supply for electric valves, but in measurement times they havn't been used. (this is with using stabilization, by taking average of last 100 readings) Light is also being measured with analog port, but appears to be working fine.
Any ideas why the soil moisture data is so bad?