ULTRASONIC_MOTION_DETECTOR

Published:2009/6/24 21:32:00 Author:Jessie | From:SeekIC

A 567 PLL IC operates in a dual-function mode as a signal generator and an FM receiver. The 567's square-wave output at pin 5 is coupled to the base of Q1, and from Q1's emitter to the input of the power amplifier (Q2 and Q6). The output drives the piezo speaker, SPKR1. The receive portion of the circuit operates as follows: transistors Q3 and Q4 are connected in a two-stage, high-gain, audio-frequency amplifier circuit, with the input connected to a second piezo speaker (SPKR2) operating as a sensitive microphone. The amplifier's output is coupled to the 567's input at pin 3. When an in-band signal is received, the LED lights. The 567's FM output is coupled from pin 2 to the input of a very-low-frequency single-transistor amplifier, Q5. The amplifier's output at Q5's collector drives a voltage-doubler circuit (C11, D1, D2, and C12). The dc output feeds a 0- to 1-mA analog meter. By placing the two pigzo speakers one foot apart and aiming them in the same direction, toward a nonmoving solid object, the signal from the transmitter's speaker urill reflect back into the receiver's speaker, and the frequency at the 567's input will be the same as the one being transmitted. The ac output at pin 2 is zero when the outgoing and incoming frequencies are the same. How-ever, when the signal is reflected from a moving object, the received frequency will be either lower or higher than the transmitted one. If the object is moving away from the speakers, the received fre-quency will be lower; if the object is moving toward the speakers, the frequency will be higher. The pin-2 signal is fed through a 470-pF capacitor to the base of Q5, where the signal is ampli-fied and fed to a voltage doubler, and then on to a meter circuit. If you wish, the voltage doubter and meter can be removed and replaced with headphones connected between the negative side of C11 and circuit ground. That will allow you to listen to the difference-frequency signal as objects move in front of the speakers.



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