Ultrasonic Burglar Alarm: Transmitter and receiver parts of the circuit are connected each other by using a triple cable. System operates with 20V supply and 10V effective output voltage drives the ultrasonic transducer at its highest value.
Transmitter circuit gives the maximum gain at 40kHz.
Ultrasonic transducers in the circuit must be placed vis-à-vis and when a barrier passes between them it must block the connection without affected from reflections.
Transmitter is continuously operating and generating 40kHz ultrasonic oscillations. Receiver is designed to operate only when no ultrasonic signal reaches it and it produces an output signal. You can connect an alarm system with a relay to the output of the receiver.