Those sound really useful. I like the no power aspect that just works.

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.

If you can do python and you can wire one part to one part, one part at a time, it's not hard, at least to me. Get the analog sensor, connect it to the analog to digital converter, connect all of their power to a relay, connect the relay and the converter to the pi, connect that to power. Then use Python to check the value in a loop, forever.

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.