I would like to be able to control my vacation house's drip system from my main home, and vice versa. Over the Internet.
Are there any devices that can retrofit the existing controller board to give web access?
What type of controllers do you currently have?
I'd have to look ... Toro or RainBird probably.
The kind you buy at the pro supply, not the big box store.
You are gonna need a smart controller with Internet capabilities. The Weather Matic smart link will probably be one of your cheaper alternatives. Here is a link http://www.smartlinknetwork.com/
In addition you should have a flow meter installed on each of you systems with a master valve. If you are gonna be away from your home for a period of time you will be able to shut your entire system down (including the main line) via computer.
There's a drawback to those "weather aware" controllers. It can rain an inch at the closest reporting station and nothing at all 1/2 mile away.
The problem with SmartLink is that they appear to charge for access to your sprinkler controller. And they aren't telling how much the service costs or what the controllers cost. I'll have to go see my supplier when I get home.
I'd hate to have to roll my own, but if I have to, I will.
There are many web-enable controllers out there. Weathermatic is a "smart" controller, high system cost plus monthly subscription.
I have a BlueSpray (www.bluespray.net). It's the best bang for the buck, IMO. It has wifi, unlimited programs. unlimited start times, probably best suited for your drip irrigation.