Circuit arrangement of an ultrasonic‐presence motion detector, particularly for a noncontact control of a water faucet

Abstract

A circuit arrangement is disclosed which is suitable for ultrasonic-presence motion detection in which an ultrasonic transducer is provided as a transmitter and an ultrasonic transducer is provided as a receiver. An oscillator produces an ac voltage for the transmitting transducer, a gate circuit is provided in order to chronologically control the feeding of wave forms of the oscillator to the transmitting transducer, and a receiver circuit is provided which is connected to a receiving transducer and which obtains a received signal from the receiving transducer. An evaluation circuit is also provided. The receiver circuit has a phase discriminator in order to recognize the value of a phase displacement between the ac voltage of the oscillator and the respective received signal. An electronic storage circuit is connected to the output side of the phase discriminator and stores the output signal of the phase discriminator at predetermined periodically recurring time points which are determined by read-out pulse signals at the respective time points. The evaluation circuit comprises a comparator circuit in order to compare the individual or several consecutive stored values of the electronic storage circuit. The comparator circuit comprises a threshold function so that an output signal of the circuit arrangement is produced when the individual stored values or the mean values of a number of consecutive stored values differ from one another by more than a prescribed value. The output signal indicates the motion-presence phenomenon.