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, 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). |
