Ultrasonic mouse repeller. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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Among the elastic vibrations of air, ultrasound, which is not perceived by the human ear (from the Latin ultra - further, more, above), has long been of particular interest to itself, the lower frequency limit for which is considered to be 20 kHz. Insects, bats and even cetaceans successfully use this natural gift: some for communication, others for hunting, others for locating the terrain and avoiding obstacles in conditions of insufficient visibility. Looking closely at the role of ultrasound in the animal world, a person takes some of the identified "patents" of nature into his arsenal. In particular, it uses a "silent" whistle. The hunter blows into it, and at this call, completely inaudible by many, a dog suddenly appears from the thicket, adequately perceiving the commands given by such a whistle.

No less popular are ultrasonic echo sounders, the analogues of which can be safely attributed to the "locators" of cetaceans and bats. Sending with the help of this device, and then receiving ultrasonic pulses reflected from the bottom, the captain of the vessel receives operational information about the depths of the reservoir.

Is for ultrasound and other work. In chemistry, for example, this is the production of finely dispersed emulsions, in medicine - the study of internal organs, in metal flaw detection - the detection of hidden shells and cracks in casting parts. Fans of popular science television programs probably remember the spectacular experience shown on central television, where a peacefully standing cup suddenly shatters into pieces, and an explanation: such destruction occurs when the frequency of ultrasonic irradiation coincides with the resonant frequency of a fragile vessel and that microexplosions provoked by ultrasound can be promisingly used for cleaning certain surfaces.

A method for obtaining a sounding air jet in laboratory conditions (a) and a siren operating on the same principle (b) as a source of air vibrations with frequencies that are multiples of the number of holes multiplied by the number of disk revolutions per second

Filter to combat self-excitation of an amplifier of electrical signals at ultrasonic frequencies

An unconventional way of obtaining ultrasound by periodic interruption of a narrowly directed air flow by a rotating disk with many holes around the circumference is curious. When the jet is stopped by the oncoming wall, a rarefaction is formed behind it, which is immediately filled with ambient air.

The spectrum of air oscillations arising in this case contains many frequencies that are multiples of the main one (unit of measurement - Hz), which is determined by the product of the number of holes in the disk and its rotation speed (rev / sec). Of course, ultrasound is also present here, which can be used for various purposes, including the fight against harmful rodents (there is evidence that mice and rats, getting used to monotonous ultrasonic vibrations, cannot tolerate periodic changes in frequency within 25-50 kHz).

And here is an example of the negative effect of ultrasound. You have to deal with it when operating devices that have electronic cascades with a high gain, when the so-called parasitic feedback of the input and output asserts itself. As a result, there is not only ultrasound partially reproduced by the emitter, from which people's ears begin to hurt, but also a hidden, in no way perceived by a person, overload of radio-electronic components, threatening their failure. Such an undesirable effect of parasitic capacitance is neutralized by introducing special (for example, resistor-capacitor) RfSfRf filters into the common power circuit of the cascades.

Radio-electronic methods are also not unsuccessful in solving other, not only technical, problems. For example, in the fight against the already mentioned rodents, using their specific reaction to ultrasound. Readers of the magazine - lovers of making everything with their own hands, can be recommended one of these anti-mouse (anti-rat) designs: an auto-switching ultrasonic emitter.

Schematic diagram and circuit board of a self-made ultrasonic emitter "Anti-rodent" (click to enlarge)

The self-made device "Anti-rodent" contains two generators of electrical oscillations, a powerful output stage and an electrodynamic emitter of ultrasonic oscillations, "swinging" the surrounding air. The main generator operating in the ultrasonic region is built according to the scheme of a symmetrical multivibrator based on transistors VT1-VT2. The corresponding switching frequency is set by the capacitance values ​​of the capacitors C1 and C2, as well as the resistance of the pairs of resistors R2-R3 and R4-R5. Subject to the ratings indicated on the circuit diagram, it is approximately equal to 25 kHz. However, if resistors R3 and R4 are shorted, the frequency will double. This is what the second generator, assembled on transistors VT3-VT4, "does" with a frequency of about seven times per second.

The ups and downs in the voltage on the VT4 collector control the VT5 transistor, unlocking and locking it. The open collector-emitter junction of this semiconductor triode shunts (through diodes VD1 and VD2) resistors R3 and R4, which causes the frequency of the main generator to increase. However, the switching of the transistor VT5 does not occur in jumps, but gradually. Thanks to the integrating chain R11C5, a kind of "walk" is obtained in the range from 25 to 50 kHz.

With the same frequencies, the transistors VT6-VT9 of the output stage operating in the key mode are switched, controlled by alternating pulses on the collectors VT1 and VT2. A high level of voltage at the load VT1 unlocks the transistor VT9, and a low level at the output of VT2 - the transistor VT6. As a result, the current from the power source flows in one half-cycle of the generator through VA1 from the bottom up, and in the other, when VT7 and VT8 are open, in the opposite direction, forcing the dynamic head to work in an unusual part of the ultrasonic range.

Parts for assembling such a radiator require the most common. In particular, MLT-0,25 resistors and capacitors KLS (C1, C2), K73-11 (C5, C6), K50-20 (C7). A "high-frequency" dynamic head of the ZGDV-1 type is suitable as an emitter.

All parts of the device, with the exception of powerful transistors VT6-VT9, are mounted on a pseudo-printed (slotted) board made of one-sided foil fiberglass 1,5-2 mm thick. Transistors VT6-VT9 are used with rectangular heatsinks, which are either mounted on a circuit board or mounted directly on the device case, excluding the electrical connection of the heatsinks to each other.

Test runs of the ultrasonic emitter can be carried out by feeding it from six galvanic cells connected in series. In normal mode, the device operates continuously, therefore, a rectifier with a filter, designed for a load current of 2,5-3 A at a voltage of 9 V, should be used for power supply.

Author: P.Yuriev

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