A control circuit (16) mounted on a faucet (10) operates an ultrasonic transducer (20) that transmits ultrasound into a target region (22) below the outlet (24) of the faucet. The control circuit receives electrical signals from the transducer when the transducer receives echoes from objects within the...http://www.google.es/patents/US4520516?utm_source=gb-gplus-sharePatente US4520516 - Ultrasonic flow-control system
