Easy Build a Cat and Dog Repeller

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 garden, 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 significantly better sense of hearing than people. Not only are their ears more sensitive, they can also perceive significantly 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.

Cat and Dog Repeller Circuit diagram :

 

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!

Read More

Dog Whistle for Ronja

Ronja is the author’s dog, a beagle-mongrel,  who seems increasingly often to need to be  called to heel either with a shout or with a  whistle. And so the idea came about for an  electronic dog whistle that could produce  two alternating high-frequency tones. A  design like this has several advantages over  conventional whistles or calling.

 

Circuit diagram :

Dog Whistle for Ronja Circuit Diagram

 

• You can continue to carry on a conversation with your friends without having to  stop to whistle or call to your dog.
• Using high frequencies means that  the whistle sound is barely audible to  (especially older) humans and so is less  annoying to other people than conventional whistles or calls. As is well known,  dogs have rather better hearing than  we do and can hear frequencies of up to  40 kHz.
• The two alternating pitches mean that the  dog can more easily distinguish it from  other whistles.

 

The dog whistle is constructed from two  standard 555 timer ICs (or a single 556 IC),  both wired as astable multivibrators. The  first 555 oscillates at around 1.5 Hz and modulates the frequency of the second, which thus  switches between two different frequencies  every 0.7 seconds or so. The output of the second 555 is connected to a piezo sounder. If the  volume from the sounder used is insufficient, a small transistor amplifier can be added  between it and the output of the second 555. The circuit draws current only when activated by pressing S1. An optional green  LED indicates that the circuit is functioning.  When S2 is pressed the output frequencies  are reduced, making them more audible to  human ears for test purposes.

 

R1, R2 and C1 set the frequency of astable  multivibrator IC1. Diode D1 ensures that the  output is a symmetrical squarewave, by making C1 charge only via R1 and discharge only  via R2. Turning to IC2, where there is no diode in the  circuit, capacitor C2 is charged via R3 and R4  and discharged only via R4. With C2 = 22nF  the 555 oscillates at about 10 kHz; with S2  pressed, and hence C3 in parallel with C2, this  falls to about 1.8 kHz. Changing C2 to 10 nF  results in an even higher frequency (about  22 kHz), which can only be heard by dogs  and certain other animals. Setting C2 to 15 nF gives an output frequency of about 15 kHz. IC1 modulates the frequency of IC2 via R5. The green LED D2 is connected to the output  of IC1 via a series resistor and thus flashes at  the modulation frequency. The output from the piezo sounder at 10 kHz  (C2 = 22 nF) should be loud enough to verify  by ear. If desired, a more efficient piezo horn  tweeter can be used instead.

 

Author : Stefan Hoffmann

Read More