Introduction to the principle of ultrasonic moving object detection device

In the figure, SPKR1 and SPKR2 are both piezoelectric tweeters, which are used to send and receive ultrasonic waves. The core of the circuit is the 567 phase-locked loop integrated circuit, which completes the dual functions of sending and receiving. The 5th pin is a square wave output, and its frequency is adjusted by R12. After being sent to Q1, its emitter is coupled to the power amplifier part composed of Q2 and Q6, and finally pushes SPKR1 to send ultrasonic waves outward. The reception of ultrasonic waves is completed by another speaker SPKR2, which is sent to the 3rd pin after being amplified by two stages of high gain of Q3 and Q4. As long as the received signal frequency is within the bandwidth of 567, LEDl can emit light.

The FM output pin of 567 is the 2nd pin. The signal is sent from this pin to the base of the ultra-low frequency single transistor amplifier stage Q5 through capacitor C9. After amplification, the collector is sent to the voltage doubler rectifier circuit Cll, D2, D1, C12 and R13, M1 through resistor R9, so that the FM signal is converted into an analog voltage and read on M1. M1 is a 0-1mA analog meter.
When working, the sending part and the receiving part are operated at the same time, and SPKR1 and SPKR2 are aimed at the detection target in the same direction, about 0.3 meters apart from each other. If the target does not move, the received ultrasonic frequency is the same as the sending frequency, the FM output is zero, and M1 has no reading. If the target moves, the receiving frequency is higher or lower than the sending frequency according to the Doppler effect, and the FM output is no longer zero. The faster the movement, the larger the reading. If the voltage doubler rectifier circuit is connected to headphones, the direction of movement can also be identified according to the height of the sound.