My larger system is entirely 12V power and is connected directly into a 2-panel 24V solar system with battery.

But entirely mechanical without external input like power is a really good idea.

ACEIRMC 2set Soil Moisture… https://www.amazon.com/dp/B09JSND12L?ref=ppx_pop_mob_ap_share

They’re just resistive electrodes with an analog sense of the conductivity of the soil, which is linearly correlated with moisture. It does this by applying a voltage to one side and sensing the current load to the other probe. This is exactly the same as electroplating, so if you keep them on 100% of the time, one will essentially dissolve in the dirt.

Instead, I run their power through a relay. I turn one relay on, it turns on all three of my sensors, I wait a few seconds, take three reads off each, one second apart, take the avg of each sensor, and record that. You can the save that to a timeseries database and host that locally too. Then plot that with Graphana.

To read the analog values, I use this: HiLetgo 3pcs ADS1115 16 Bit 16… https://www.amazon.com/dp/B07VPFLSMX?ref=ppx_pop_mob_ap_share

Now that you have logs, you can check moisture levels before activating your irrigation.

The next step is I have a set of float sensors in the rain barrel, towards the bottom. If the bottom one indicates empty it activates a solenoid to refill from the tap until the top one indicates full. They’re about two inches apart.

Yes I actually have two of them. My backyard has three outdoor moisture sensors, so it can know if it’s moist enough. It has a drop irrigation system connected to regular plastic pressure for tubing. It has two zones that can be controlled with two solenoids. It also has a 12V pump. All of that is powered by a 12V power supply and controlled by a four zone relay board. Remember to turn the power off to your outdoor sensors so that they don’t destroy themselves when you’re not sensing. You can also add a flow sensor to measure your water consumption.

I have a PiHole, my own EdgeRouter that is behind the Verizon router, a UPS, a wired switch, a SiliconDust HD HomeRun to convert my cable to a stream, my Hue controller, my Camera DVR, and a Pi4 hosting network storage.

It all fits neatly in a 6U closet rack. I use the EdgeRouter to host a VPN I can connect into to manage things for the house, and also use it to dial out to a VPN, so I can connect the TVs in the house to a VPN abroad.

I also have a Smart Garden powered by a raspberry pi, connected to a rain barrel, a water pump, some solenoids, and some moisture sensors.