Ray has built nice water valve controller that fit into mint tin. The minty project based on Arduino pro mini to control orbit yard watering valve. It uses RF link 434MHz transmitter and receiver module for wireless control. As power source, the project comes with single 3.6v li-poly rechargeable battery. Since the valve solenoid need 24V, the battery voltage need to be boosted momentarily using LT1303 DC/DC step-up converter before connected to valve selenoid.
Other feature that may be added in the future for this project including timer control the valve, installing a rain sensor to delay watering when it rains, or use weather reports from online websites for intelligent watering.
Project Firmware, Schematic and Documentation