Ultrasonic guard. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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From here we will take only a generator-emitter that can work in any security system that uses ultrasound.
On fig. 1 shows a schematic diagram of a generator that excites an ultrasonic piezoelectric emitter of the UM-1 type, recommended by its manufacturers. However, such a generator is often excited not at the fundamental frequency of the radiator, but at much higher spurious frequencies. In this case, on the "microphone" UM-1 (these resonators have a rather narrow bandwidth and are sold in pairs), the signal will obviously simply be absent.
In the generator, the schematic diagram of which is shown in Fig. 2, measures have been taken to ensure that the piezoresonator is excited only at its fundamental frequency. It consists of two blocks - a self-excited oscillator, made on a DD1 chip, and a synchronizer, which includes an R7C3 frequency-limiting chain and an amplifier (VT1, etc.).
Transistor VT1 - any silicon, with a current gain of 50 ... 300 and a voltage Uke of at least 15 V (KT315G, KT315E, KT3102A-KT3102V, a number of others3). The K561LN2 microcircuit can be replaced by the one of the same name from the 564 or KR1561 series. Capacitor C1 should be as thermally stable as possible (an oscillator with C1 from the TKE M75 group confidently "kept" the resonant frequency in the temperature range of +25 ... -20 ° C). Trimmer resistor R5 - type SP5. This resistor has a fairly high stability of the set resistance.
Setting up the generator is simple. By connecting an oscilloscope to resistor R6 and shorting capacitor C3, by adjusting resistor R5, the generator is brought into operation at the fundamental frequency of the piezoelectric emitter (it will correspond to a sharp increase in the amplitude of oscillations on the oscilloscope screen). By removing the jumper from the capacitor C3, they make sure that the synchronizer works: with fairly significant changes in the resistance of the resistor R5, the frequency and amplitude of the generated oscillations should remain practically unchanged.
Author: Will W.; Publication: cxem.net
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