Cat and Dog Repeller

Description: In modern households, outdoor lamps equipped with motion sensors are commonly found. These devices provide illumination upon approach, enhancing safety and convenience while also deterring potential intruders. However, free-roaming pets, such as dogs and cats, often disregard these lamps and continue to leave waste in gardens where they have established habitual spots. This scenario led to the concept of integrating a siren in parallel with the outdoor lamp to signal to pets that they are unwelcome. To avoid disturbing the entire neighborhood with loud alarms, the design can utilize the superior hearing capabilities of dogs and cats. Unlike humans, who can hear frequencies up to around 18 kHz, these animals can detect sounds above 20 kHz. Therefore, a siren emitting a frequency just above this threshold can effectively repel pets without being audible to humans. The implementation requires an oscillator with an amplifier and a high-frequency tweeter, such as a piezoelectric tweeter. The schematic illustrates the straightforward construction of this circuit. The power supply for the circuit is derived from components up to and including capacitor C2. The 230-V mains supply connects in parallel with the motion-sensor lamp. Capacitor C1 and resistor R1 facilitate capacitive coupling to reduce the 230 V to a manageable level. A DC voltage of approximately 9.1 V is produced via a bridge rectifier and diode D1, followed by filtering and buffering through capacitor C2. The oscillator circuit, comprising resistor R3, capacitor C3, and integrated circuit IC1a, generates the desired frequency. The oscillator's frequency is contingent upon the characteristics of IC1, so the specified component values should be viewed as guidelines. Increasing R3 and/or C3 will lower the frequency, while decreasing these values will raise the frequency. The square-wave output from the oscillator feeds into an H-bridge formed by several Schmitt triggers and the final output stages (transistors T1 to T4). This configuration results in a peak-to-peak voltage that is double the supply voltage, yielding approximately 18 V across the piezoelectric tweeter, which produces a sufficiently loud whistle. It is critical to ensure safe handling, as the circuit operates directly from the 230 V mains and lacks electrical isolation. Consequently, all components must be housed in a well-insulated, waterproof enclosure. For testing, it is advisable to discharge capacitor C1 with a resistor, as it can retain a hazardous charge. Additionally, components F1, C1, R1, and B1 must maintain a mutual insulation separation of at least 6 mm to ensure safety.

The circuit design effectively addresses the challenge of deterring unwanted animals while maintaining a quiet environment for humans. The use of high-frequency sound waves capitalizes on the auditory capabilities of pets, ensuring that the alarm is effective without being disruptive. The oscillator's design allows for frequency adjustments, enabling fine-tuning based on the specific characteristics of the components used. The H-bridge configuration amplifies the signal to drive the piezoelectric tweeter efficiently, ensuring that the alarm is both powerful and effective. Proper insulation and safety precautions are paramount due to the direct connection to mains voltage, highlighting the importance of careful construction and testing. This design not only resolves a common nuisance but also does so with an innovative approach that leverages the distinct sensory abilities of animals.Nowadays, just about every house has an outside lamp with a motion sensor. Such a device eliminates the need to feel your way to the front door, and it apparently also scares away intruders. The only problem is that free-running dogs and cats in the neighborhood have little regard for such lamps and continue to deposit their excrement in the garde

n, once they have found a habitual location there for this purpose. This gave rise to the idea of connecting a sort of siren in parallel with the outside lamp to clearly advise dogs and cats that they are not welcome. Naturally, it would be nice to avoid startling the entire neighborhood with this alarm signal. Here we can take advantage of the fact that dogs and cats have a signicantly better sense of hearing than people.

Not only are their ears more sensitive, they can also perceive signicantly higher frequencies. With people, the upper limit is around 18 kHz, but dogs and cats can hear frequencies in excess of 20 kHz. We can take advantage of this by building a siren that emits a frequency just above 20 kHz. This will scare off dogs and cats, but people will simply not hear it. All we need for this is an oscillator with an amplifier stage and a tweeter that can reproduce such high frequencies, such as a piezoelectric tweeter.

The schematic diagram shows how easily this can be implemented. The power supply for the entire circuit is formed by the components up to and including C2. The 230-V leads are connected in parallel with the motion-sensor lamp. C1 and R1 provide capacitive coupling to reduce the 230 V to an acceptable voltage. A DC voltage of approximately 9. 1 V is generated from this voltage using a bridge rectifier and D1, filtered and buffered by C2. The oscillator is built around R3, C3 and IC1a. The frequency of this oscillator is rather dependent on the specific characteristics of IC1, so the values shown here should be regarded as guidelines. If the oscillator frequency is too high, it can be reduced by increasing the value of R3 and/or C3. If the frequency is too low (which means that the siren tone it is audible), the value of R3 and/or C3 should be increased.

The square-wave signal from the oscillator is applied to the input of an H bridge composed of several Schmitt triggers in combination with the final output stages (T1 T4). This approach causes the peak-to-peak value of the square wave signal to be twice the supply voltage.

As a result, a respectable 18 V is obtained across the piezoelectric tweeter, which is sufficient to produce a quite loud whistle tone. When building the circuit, you should bear in mind that it is directly powered from 230 V and not electrically isolated from the mains network.

It is thus necessary to avoid contact with all of the components when the circuit is in use. In practice, this means that the circuit must be fitted into a well-insulated, waterproof box. If you want to test the circuit, it is a good idea to first discharge C1 using a resistor, since it can hold a dangerous charge. You must also ensure that components F1, C1, R1 and B1 all have a mutual insulation separation of at least 6 mm!