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An intrusion alarm circuit including a single electroacoustical transducer, such as a diaphragm-supported piezoelectric element, connected to an amplifier in a positive feedback loop configuration. The transducer functions as both a sound pickup and sound generator. When the ambient sound level exce

An intrusion alarm circuit including a single electroacoustical transducer, such as a diaphragm-supported piezoelectric element, connected to an amplifier in a positive feedback loop configuration. The transducer functions as both a sound pickup and sound generator. When the ambient sound level exceeds a preselected threshold level, the resulting vibration of the transducer generates a voltage which activates the amplifier, whereupon the transducer vibrations are sustained and amplified in the manner of an oscillator, thereby producing an audible alarm.

대표청구항 ▼

An audio transducer circuit responsive to the detection of sound above a predetermined threshold level for producing an alarm, said transducer circuit comprising: an electroacoustical transducer having a plurality of terminals; a source of DC voltage; a first switching amplifier coupled to said DC s

An audio transducer circuit responsive to the detection of sound above a predetermined threshold level for producing an alarm, said transducer circuit comprising: an electroacoustical transducer having a plurality of terminals; a source of DC voltage; a first switching amplifier coupled to said DC source and biased to be normally nonconducting; means coupling voltage output terminals of said transducer to the input of said first amplifier whereby activation of said transducer by sound above said predetermined threshold level causes a voltage of sufficient magnitude to be applied to said first amplifier to overcome the bias thereon and render said first amplifier conducting, said threshold level thereby being determined by the selected bias of said first amplifier; and means coupling the output of said first switching amplifier to drive terminals of said transducer, said circuit thereby forming a threshold triggered oscillator.