Yes what you’re asking about can definitely be done. I’ve done something very similar and it’s been working for a few years now. A few thoughts about your proposed setup come to mind.
- I’d suggest a more robust soil moisture sensor. I’ve got a chirp and mine definitely is not designed for outdoor use. I’d suggest considering the VH400. I’ve also got one of these and it is now in its 4th season outdoors in the containers on my deck. I’ve had absolutely zero problems with it. It uses the same method to measure soil moisture as the chirp.
- If the only thing you’re doing with the Raspberry Pi Zero W is using it to read the value from the chirp and send the data to Opensprinkler over WiFi, you should probably use an ESP8266 or ESP32. It’ll use way less power. That will mean you’ll need a much smaller battery and a smaller solar panel also. Just make sure that whichever version you choose you’ve got an analog to digital converter on it (ADC) if you use the VH400 as it outputs an analog signal.
- Instead of changing the waterlevel on the Opensprinkler, you could just turn the zone on through an API command. Seems more straightforward to me.
I’ve mentioned my setup before on the forum. Here’s a link to one of the mentions. https://opensprinkler.com/forums/topic/pi-customisation/ If you have any questions just ask.