In the Ultrasonic anti-theft alarm circuit , the main components are the Ultrasonic Transmitter (UCM40T) and Ultrasonic receiver (UCM40R). The transmitter and receiver can be placed where theft fear is there.
IC4, ie 555IC generates the signals with a frequency of 40 Hz (Ultrasonic signal frequency is – 40Hz). As the signal is very week, it is amplified by two NOT gate IC’s (IC3- which are present near UCM40T). This is transmitted by the ultrasonic transmitter. Normally the receiver does not receive any signal. When anybody enters the ultrasonic zone, ie between the transmitter and receiver, then, the receiver receives the signal from the transmitter.
The receiving signal will also be so week, that it cannot drive any components. So, if any signal is received by the receiver, it is then amplified by two op-amp ICs, which are amplifier IC’s ie, IC1a, IC1b and IC2. And here, it is again amplified by using two NOT gate ICs’s CD4011. The amplified signal is then send to a LED for indication. The end of the circuit can also be connected to a speaker or buzzer or to drive any other circuit with an operating voltage of 12V.