ULTRASONIC_SWITCH

Published:2009/6/30 3:12:00 Author:May | From:SeekIC

Receiver. Output from the transducer is amplified by Q1 and Q2, and rectified by D1. Voltage on pin 2 of IC1 will go more negative as the input signal increases. IC1 is used as a comparator and checks the voltage on pin 2 (i.e., the sound level), to that on pin 3 which is the reference level. If pin 2 is at a lower voltage than pin 3 (i.e., a signal is present), the output of IC1 will be high (about 10.5 volts) and this will turn on Q3 which will close the relay. The converse occurs if pin 2 is at a higher voltage than pine 3.Transmitter. The oscillator frequency is determined by the transducer characteristics [(minimum (series resonance) at 39.8 kHz fol-lowed by a maximum (parallel resonance) at 41.5 kHz.)] Two transistors from a noninvert-ing amplifier and positive feedback is supplied via the transducer, R6 and C3. At the series resOnant frequency, this feedback is strong enough to cause oscillation.



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