Cat And Dog Repellent

The electronic dog
repellent circuit diagram below is a high output ultrasonic transmitter
which is primarily intended to act as a dog and cat repeller, which can
be used individuals to act as a deterrent against some animals. It
should NOT be relied upon as a defence against
aggressive dogs but it may help distract them or encourage them to go
away and do not consider this as an electronic pest repeller. The
ultrasonic dog repellant uses a standard 555 timer IC1 set up as an
oscillator using a single RC network to give a 40 kHz square wave with
equal mark/space ratio.

This frequency is above the hearing threshold for humans but is
known to be irritating frequency for dog and cats. Since the maximum
current that a 555 timer can supply is 200mA an amplifier stage was
required so a high-power H-bridge network was devised, formed by 4
transistors TR1 to TR4. A second timer IC2 forms a buffer amplifier that
feeds one input of the H-bridge driver, with an inverted waveform to
that of IC1 output being fed to the opposite input of the H-bridge.

Cat And Dog Repellent Circuit

Cat And Dog Repellent Circuit Diagram

This means that conduction occurs through the complementary pairs of
TR1/TR4 and TR2/TR3 on alternate marks and spaces, effectively doubling
the voltage across the ultrasonic transducer, LS1. This is optimised to
generate a high output at ultrasonic frequencies. This configuration
was tested by decreasing the frequency of the oscillator to an audible
level and replacing the ultrasonic transducer with a loudspeaker; the
results were astounding. If the dog repellent circuit was fed by a bench
power supply rather than a battery that restrict the available current,
the output reached 110dB with 4A running through the speaker which is
plenty loud enough!

The Dog and Cat repellant was activated using a normal open switch
S1 to control the current consumption, but many forms of automatic
switching could be used such as pressure sensitive mats, light beams or PIR
sensors. Thus it could be utilise as part of a dog or cat deterrent
system to help prevent unwanted damage to gardens or flowerbeds, or a
battery powered version can be carried for portable use. Consider also
using a lead-acid battery if desired, and a single chip version could be
built using the 556 dual timer IC to save space and improve battery
life.

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