I know you are kind of working on this generally but I’m not really sure what you have in mind for the end result. So I thought I’d send in my 2 cents. They aren’t completely thought through though. That said, I operate a weather station and publish data to Wunderground and the NWS. Instead of downloading data from an internet site I could set up a URL on my local network to pull the weather data from. It get’s updated every 5 minutes.
* Instead of setting how much time to water, it would be nice to tell it how much water is required in addition to the ET rate and let it calculate how long to water the zone. You’d probably have to type in the square feet covered by the zone as well as the flow rate for the zone to do that. For a grass zone it would probably be watering early in the morning, based on the ET rate for the prior day maybe?
* Only water if the wind is below a certain level. We get lots of wind here and for the grass sprinklers they probably wouldn’t do much good when it’s over 15 MPH or so. However the garden uses drip lines so that’s not affected – ie it would need to be on a per zone or program basis.
BTW here’s some information on how to use ET to calculate watering time. It’s specifically for grape vines but the methodology seems like it would be applicable to anything with the proper conversion factors.
I’m working on a program to calculate required watering time based on rainfall in last few days and predicted rainfall in next few days, based on a weekly watering requirement (1in/week for my area). I’m using wunderground API to get the required data. I’m new to programming (this is my first real programming project), so it will be quite simple, but I’m sick of my sprinklers going off just right after it rained or when its about to rain.