Wireless network keeps grass green

Forgetting to water the lawn, or overwatering and drowning it will be worries of the past if engineers at Digital Sun Inc., San Jose, Calif., have their way. They've developed a sprinkler system that includes sensors stakes that are inserted into the lawn. The stakes measure the capacitance differential between different moisture levels in the ground to determine if the lawn needs watering. If it does, the sensor transmits a signal to the control unit up to 200 ft away, which switches on the sprinklers. Sensors also indicate when the soil is properly saturated and watering can cease. A sensor network can monitor lawns that stretch further than 200 ft from the control unit. That's because sensors not only send signals, they also relay them. Sensors transmit at 900 MHz and run on a standard AA battery. A display on top of each sensor lets users manually check the soil's water content. The system sounds an alarm if it detects a broken or clogged sprinkler head.