Scare off the unwanted guests like Rats and Cats from your home. This Ultrasonic transducer emits inaudible ultrasound which makes a hostile environment for the pests like rats. Even though human beings cant hear ultrasound, most of the animals can hear the ultrasound. Some frequencies of the ultrasound create stress on the animals and they avoid its presences. Animals like Rats, Cats, Dogs etc responds to the ultrasound frequencies between 28 kHz and 60 kHz. The output frequency of this circuit can be varied from 20-60 kHz using a Pot. Remember, animals are more intelligent and adapted than us and sometimes they will be immunized to a particular frequency.
IC CD4047 is used an Astable multivibrator with timing components C1, VR1 and R1. By adjusting the Pot, different frequencies of ultrasound can be selected. Since Ultrasound is inaudible to us, it is necessary to realize the exact frequency at which the pests respond through trial and error. If an Oscilloscope is used, the Pot can be calibrated.
Use a 22K Lin (Linear) volume control as Pot and a Piezo tweeter for good results. Earphone tweeter of telephone is a good choice.