Proximity detector circuit

A very simple ultrasonic proximity detector circuit can be constructed using few external electronic components . As you can see in the circuit diagram shown here, this proximity detector circuit require some external components and is very easy to build. 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 .

If an solid object is moved in close proximity to the front of the buzzer , the relays drops out .
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 .