Ultrasonic proximity detector circuit

This ultrasonic proximity detector circuit is designed using few external electronic components .
If an solid object is moved in close proximity to the front of the buzzer , the relays drops out .
The R4 ( 100k ohms potentiometer ) sets the current fed to the buzzer ( sounder) . The potentiometer must be adjusted to a sounder point where the buzzer begins to sound .
The Q1 transistor is coupled to the positive side of the sounder , and its output is fed to a voltage doubler circuit .The base of Q2 transistor is driven by the output of voltage doubler circuit , which activate the relay . As long as the buzzer sounder produce an audible sound , the relay stays energized .
This simple ultrasonic proximity circuit described here needs to be powered from an 12 volts DC power supply , so you will need to use an 12 volts electronic relay .