“Ah, summer red, I would love you, if not for the heat, and dust, Yes mosquitoes, Yes flies”. And although the high poetry of the great poet little combined with the dry prosaic lines, technical articles, these words can be safely put as the epigraph to this material. To stop the change of seasons in nature is impossible, and every year we have a “happening” summer, and with it come the usual worries of relief and localization of negative emotions, invariably manifested in humans with the appearance of annoying flying insects — mosquitoes, flies and other midges. To protect yourself from them, in nature and even at home someone buys a mosquito net, others treat themselves and family members with special insect repelling creams and formulations. However, possessing the skills, you can build a simple circuit protection device against mosquitoes, operating by using of ultrasonic radiation. What is ultrasound?
Ultrasound is an elastic wave high frequency. The human ear perceives the forward propagating elastic wave with a frequency of approximately 16, OOO cycles per second (Hz), oscillations with higher frequency are ultrasound (beyond the limit of audibility). Usually the ultrasonic range is considered the frequency band from 20, OOO to several billion Hertz. The fact that the ultrasound actively influences on biological objects (for example, kills bacteria), has been known for over 80 years. One of the useful qualities of ultrasonic radiation is to combat flying insects.
Consider a device, scheme of which is presented in figure 1. Such features of the device, as available details, small size and lack of establishment, allowing you to repeat it to any radio Amateur. Directly to hear the emitted sound (and thus to verify the health of the host) is not possible. But on the collector of transistor VT2 (if necessary) it is possible to control a pulse frequency of 32 to 40 kHz. In the circuit of the same type transistors VT1, VT2 assembled the high-frequency oscillator, which is loaded on the piezoelectric primer HA1. The limiting resistors R1, R3, R6, rectifier diode VD2 and the oxide capacitor C1 perform the role of a transformerless power supply for the ultrasonic generator. Current consumption is less than 20 mA. Voltage generator (the difference of potentials on the plates of electrolytic capacitor C1) can be in the range of 10…15 V.