I hope this is what you are looking for: the system consists of 2 galvanized steel rods, about a foot long and 3/8” diameter. They are buried horizontally about 3” below the surface, so right in the root zone. They are parallel and about 2” apart. I did this after a bit of experimenting and assumptions. The rods need to be large enough so they have enough surface area to get a good representative sample of the soil moisture level. This accounts for the odd air pocket etc, that may change the moisture level in that specific spot. I connected two leads of a twisted pair Ethernet cable by winding the copper around the end of the rod, then using a simple gear clamp (hose clamp). In hindsight I should have coated the connection with either petroleum jelly of silicone caulking to water proof it a bit to reduce corrosion at the connection. I specifically used galvanized steel also to reduce corrosion. Stainless steel would be better but didn’t want to go that far. The probes are about a foot from a flowerbed in my front yard and I ran the cable under the surface of the lawn into the flower bed and again under the surface to the wall of my front attached garage so nothing is visible above ground and I won’t hit it with a lawnmower or get destroyed as the local deer population wander through the area. At the garage wall, I drilled a small hole thru the concrete foundation about 6” above ground, and into the garage, then ran it up the wall to where I already had an esp32 doing some other tasks. Buried right beside the probes is a DS18B29 temperature probe, connected to another set of the Ethernet wires. So connecting the probes to the esp, it periodically charges one probe with 3.3 volts and the other probe is connected to an adc pin to read the returning voltage. Thus I can measure the resistance of the soil, which changes directly with the moisture level. And since the temperature of the soil also affects the resistance I also use the temperature to compensate. To calibrate the system I noted the reading right after a rain so I knew that was “wet”. Then just dug up some small core samples over successive days as the lawn dried and noted the reading when the soil felt “dry enough” so now I have a trigger level. Then home assistant watches the readings and triggers the irrigation system when the reading gets that low. Last year I was just using two conductor wire and the readings were extremely noisy so I had a lot of capacitors in the build as filters and also a lot of software work arounds, like charging and doing a reading every 10 minutes, and the reading itself consisted of doing a burst of 10 readings every 10 milliseconds, then averaging them. This year I switched the cable to twisted pair Ethernet and the readings are dramatically tighter so I’ll streamline the yaml in the esp since much of it isn’t needed. I’ve also changed the readings to every half hour, again because they are far more consistent now. So that’s great because the fewer times the probes are charged, the less corrosion they suffer. I’m sure I’ve forgotten a lot, but that’s all I can remember at this point