Ultrasonic burglar alarm circuit diagram and detailed explanation

The ultrasonic burglar alarm detection circuit directly uses the ultrasonic reflected signal and outputs the control signal after receiving amplification processing through the receiver. The circuit is suitable for use in open open spaces. In this kind of site, there is usually no reflected signal, only the reflected signal formed after the moving object enters the detection area is received by the receiver, and the control signal can be output after processing. The structure of this circuit is relatively simple.
How it works
The circuit schematic diagram of ultrasonic burglar alarm detector is shown in the figure, the circuit adopts a one-piece structure, and the transmitter and receiver are mounted on the same circuit board. The installation of the ultrasonic transmitter and receiver heads is shown in the figure.
The principle of the ultrasonic transmitter circuit is shown in the figure, consisting of a multivibrator composed of a 555 circuit, and its oscillation frequency is 40kHz. RPI is used to calibrate the oscillation frequency. The 40kHz pulse generated by the multivibrator is output by three pins, buffered and shaped by D1 and D2, and emitted outward through the ultrasonic transmitter UCM40-T.
Ultrasonic receiver circuit, this circuit includes ultrasonic receiver head, voltage device, detection circuit and monostable delay circuit.
Ultrasonic receiver head UCM4a-R receives and converts the ultrasonic waves reflected by moving objects into electrical pulse signals, and after the high-frequency filter circuit composed of R5 and C4 filters out the interference pulses, it is adjusted by RP2 voltage divider, and C5 and R6 are coupled to the voltage amplifier for voltage amplification. The RP2 doubles as a potentiometer for the load and reception sensitivity of the ultrasonic receiver.
The operational amplifiers IC2a and IC2b form a two-stage voltage amplifier. The magnification of the first stage amplifier is R9/R6 two 45 times, the amplification of the second stage amplifier is RiiIR, o=45 times, and the total amplification of the two-stage amplifier is 45 x 45 two 2025 times.