I’m in the process of building my first greenhouse. It’s taking up half of my garage right now. That’s holding me up from working on this moisture sensor project.
It sounds like you may not need any OpenSprinkler product. Just run 24 volts to the relay control board with a moisture sensor attached. If it’s dry it’ll turn on. If it’s wet it’ll turn off. Very simple. You’ll only have one on/off threshold though. Would be better to have separate on and off thresholds. That would help avoid short-cycling. Bury the sensor deep enough though and it may be all you need. My plan with the moisture sensor integrated with my OSBo is to have the moisture sensor trigger when to start watering, water for some adjustable amount of time and then shut the water off. That’ll all be handled on the software side of things.