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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Birdsong simulator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators The device, the scheme of which is shown in fig. 1 produces a complex audio frequency signal reminiscent of birdsong. The basis for it was a somewhat unusual asymmetric standby multivibrator, assembled on two bipolar silicon transistors of different conductivity. The power supply GB1 (battery "Korund") through connector X1 is permanently connected to the cascade on the transistor VT2, which is separated from the first cascade on the transistor VT1 by the normally open button SB1. A feature of the device is the presence of three timing circuits, which, in fact, determines the nature of the sound effect. The simulator does not have a general power switch, since the current consumption in standby mode does not exceed 0,1 μA, which is much less than the battery self-discharge current. The device works like this. One has only to press the button SB1, and the capacitor C1 is charged to the voltage of the battery GB1. After releasing the button, the capacitor will power the transistor VT1. It will open, and the base current VT2 will flow through its collector-emitter junction, which will also open. This is where the RC positive feedback circuit, made up of resistor R2 and capacitor C2, comes into play, and the generator is excited. Since the input of the generator is relatively high-resistance, and the resistor R2 connected in series with the capacitor C2 has a large resistance, a current pulse of considerable duration will follow. It, in turn, will be filled with a "pause" of shorter pulses, the frequency of which lies within the audio range. These fluctuations arise due to the presence of a parallel LC circuit, consisting of the inductance of the BF1 capsule winding, its own capacitance and the capacitance of the capacitor C3, connected by alternating current in parallel with the BF1 winding. Due to the non-linearity of the charge-discharge process of capacitors C2 and C3, sound vibrations will be additionally modulated in frequency and amplitude. The result is a sound played by the BF1 phone as a whistle, which continuously changes timbre, and then breaks off - a pause follows.
After the discharge of the capacitor C2, a new cycle of its charge begins - the generation resumes. With each subsequent sound, as the voltage on the capacitor C1 decreases, the whistle melody becomes different, increasingly interspersed with a click characteristic of bird singing, and the volume gradually decreases. At the end of the "trill" a few quiet, gentle, fading whistles are heard. After that, the voltage at the base of VT1 will fall below the threshold for opening it (about 0,6-0,7 V), both galvanically connected transistors close, and the sound stops. After some time, the capacitor C1 is completely discharged (through its own internal resistance, the resistor R1, the transistor VT1 and the emitter junction VT2), the circuit formed by the elements R1, C1, VT1 is connected between the base and the emitter of the transistor VT2, locking it even more and thereby providing a high economy of the device in standby mode. The simulator is resumed by pressing the button again. The device can use transistors of the KT201, KT301, KT306, KT312, KT315, KT316, KT342 (VT1) series; KT203, KT208, KT351, KT352, KT361 (VT2) with a static current transfer ratio of at least 30. Any small-sized resistor R1, for example MLT-0,125, tuning resistor - SPO-0,4, SP3-9a. Capacitors C2, C3 - MBM (KLS, K10-7V), C1-oxide, for example K50-6. Phone BF1 - capsule DEMSh-1, a miniature "earphone" TM-2A (the plastic nozzle is removed in it - the sound guide) or another, but always electromagnetic, with a winding resistance of up to 200 Ohms; button KM1-1 or MP3. Establishment comes down to selecting the position of the tuning resistor engine, at which the desired sound effect is reproduced. The nature of "singing" is easy to change by selecting the following elements empirically: C1 within 20-100 microfarads (determines the total duration of the sound), C2 within 0,1-1 microfarads (the duration of each individual sound). In addition, C2 and R1 (within 470 kΩ - 2,2 MΩ) determine the duration of the pauses between the first and subsequent sounds. The timbre coloring of sounds depends on the capacitance of capacitor C3 (1000 pF-0,1 uF). Author; E. Savitsky, Korosten, Zhytomyr region; Publication: cxem.net
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