There have been an number of circuits discussed here to detect soil moisture. Most use conductivity of the soil though there is one reference to using a galvanic cell to generate a voltage. What is the preferred method? AND none of the circuits have any protection from charged soil (e.g. from a lightening strike -- of course taking a direct hit is probably un-surviveable). Some even fed the output directly into a micro controller which sounds like a nice cloud to ground strike within a mile would likely cook the MCU.
So, best type (direct measurement of conducted current? 555-based? AC? DC? galvanic cell? ??) Others?
I will read the output with a micro controller so anything that might be included in the MCU need not be duplicated in the sensor circuit.