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It 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, freque- ncy 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 |
