Given what I've said above, I'd love to see a public domain project, maybe use a Rasberry Pi. More than enough CPU and RAM on board to drive it and could easily compute everything we've discussed. A public domain project that would be highly customizable to meet anyone's needs. Hmmmmm.
Edit: People are already doing it! Google: Rasberry Pi Sprinkler
I emailed BlueSpray and asked. Targeted price is $199. If you include the wireless bridge with IC, BlueSpray is a better deal, IMO. What else do you expect a sprinkler controller hardware to do?
I've used a rain sensor, and it's not very accurate. I set it to the least amount of rain 1/8", it still takes a big rain for at least half an hour before the sensor is triggered. No matter how much it rains. the sensor dries out within hours after the rain. So it would still water the lawn when it rains and waters again too soon after the rain.
I haven't seen a reliable soil moisture sensor. Problem with these is that you have to bury them. Burial subjects it to corrosion and lawn mower. There is a new wireless moisture sensor out there call ug???. Problem is, it cost $300 per zone - yikes.
The most economical thing is the weather, IMO, which you can pull down for almost free from the web. It's not the most reliable method, but better bang for the buck.
Your comment on the use of weather reporting data for input is a great idea. If there is some way to integrate external weather data into a watering decision tree, that definitely could be a valuable assist. One could see using a big time weather report (weather.com, weather.gov), and a home use weather station too. Collectively that would be a great way to deliver a reasonably sophisticated home watering system.
Using the Google link for "Rasberry Pi Sprinkler", I see where someone is already developing exactly the same thing that BlueSpray mentions - sprinkler controller and garage door opener. Wonder if that's what BlueSpray is doing?
Seems to me that someone could sell a "kit" with a housing for the Rasberry Pi, relay circuitry and components (to trigger the sprinklers), and a power supply. It would be great for the software to have a public domain core, so the community of users could grow the source code to do anything one would need in the world of residential sprinkler use. Of course, as a controller, it could really be grown to control far more than just sprinkers, but you have to start somewhere!
This post has been edited 2 times, last edit by "eganders" (Dec 4th 2012, 5:19pm)