Electronic circuits > Audio > Ultrasonic pest repellent
Ultrasonic pest repellentIt is well know that pests like rats, mice etc are repelled by ultrasonic
frequency in the range of 30 kHz to 50 kHz. Human beings can’t hear these
high-frequency sounds. Unfortunately, all pests do not react at the same
ultrasonic frequency. While some pests get repelled at 35 kHz, some others get
repelled at 38 to 40 kHz. Thus to increase the effectiveness, frequency of
ultrasonic oscillator has to be continuously varied between certain limits. By
using this circuit design, frequency of emission of ultrasonic sound is
continuously varied step-by-step automatically. Here five steps of variation are
used but the same can be extended up to 10 steps, if desired. For each clock
pulse output from op-amp IC1 CA3130 (which is wired here as a low-frequency
square wave oscillator), the logic 1 output of IC2 CD4017 (which is a well-known
decade counter) shifts from Q0 to Q4 (or Q0 to Q9). Five presets VR2 through VR6
(one each connected at Q0 to Q4 output pins) are set for different values and
connected to pin 7 of IC3 (NE555) electronically. VR1 is used to change clock
pulse rate. IC3 is wired as an astable multivibrator operating at a frequency of
nearly 80 kHz. Its output is not symmetrical. IC4 is CD4013, a D-type flip-flop
which delivers symmetrical 40kHz signals at its Q and Q outputs which are
amplified in push-pull mode by transistors T1, T2, T3 and T4 to drive a
low-cost, high-frequency piezo tweeter. For frequency adjustments, you may use
an oscilloscope. It can be done by trial and error also if you do not have an
oscilloscope. This pest repeller would prove to be much more effective than
those published earlier because here ultrasonic frequency is automatically
changed to cover different pests and the power output is also sufficiently high.
If you want low-power output in 30-50 kHz ultrasonic frequency range then the
crystal transducer may be directly connected across Q and Q outputs of IC4
(transistor amplifier is not necessary).
![Ultrasonic pest repellent](images/audioe/6_small.gif)
Published on: 2004-08-21 (28802 reads)
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