Can the OpenSprinkler be modified or adapted to utilize DC latching solenoids on the irrigation control valves? I’d love to be able to try this system, but all the locations where I would want to use it do not have AC power. I currently use battery operated controllers (such as the ones made by DIG Corporation or Hunter Industries) and 9 volt DC latching solenoids. The advantage to these solenoids is that they only require a 10 millisecond pulse to open the valve, and they do not draw any current while the valve is watering. The disadvantage is that the voltage polarity must be reversed in order to close the valve.
It will be tricky to design an add-on circuit to use OpenSprinkler with DC latching solenoids. I would recommend keeping an eye on the upcoming OpenSprinkler Bee: http://rayshobby.net/cart/osbee-10
which is designed to operate on battery and interface with DC latching solenoids. I’ve just ordered semi-final PCBs and expect to roll it out within a month or two (finally!)