Electric bell-canary. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators
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An electric apartment bell can sound like a canary if you mount a simple device according to the following scheme.
The call consists of a "canary" generator (transistors V1, V2) and a time delay machine (transistors V3 and V4). The latter is necessary so that the sounding time of the canary trill does not depend on the time the doorbell button S1 is pressed.
The multivibrator is assembled on transistors V1 and V2, in addition, the transistor V2 is part of the blocking oscillator, the frequency of which changes smoothly during the operating cycle, and the duration of operation depends on the frequency of the multivibrator. As a result, trills are heard periodically (with pauses of 1 ... 10 s) in head B15, imitating the singing of a canary.
As a transformer T1, an output transformer (TV) from small-sized pocket receivers with a push-pull LF amplifier was used. Coil L1 is the primary winding of a matching transformer (TC) from the same receivers. Head B1 - 0,25 GD-10; resistors - MLT-0,125 (R7 - wire, made of wire with high resistivity); capacitors C1, C2, C4, C6 - K50-6; C3, C5 - KLS; power source - battery "Krona".
Trill repetition frequency can be changed by selecting resistor R5. Resistor R7, connected in series with the head, affects not only the volume of the sound, but also the frequency of the blocking oscillator. This resistor can be selected experimentally, temporarily replacing it with a variable (wire) resistance of 2 ... 3 Ohm.
The time delay machine is powered by a 1 V source GB9. The timing chain is capacitor C6 and resistor R9. In the initial state (when the bell button is not pressed), capacitor C6 is connected through relay contacts K1, K1.1 and resistor R8 to the power source and is charged to its voltage, and transistors V3 and V4 are closed. When the S1 button is pressed, its contacts are closed and the charged capacitor is connected to the resistors R9 and R10. A negative bias voltage appears at the base of transistor V3, and it (as well as transistor V4) turns on. Relay K1 is activated and contacts K1.1 blocks the contacts of the button.
Capacitor C6 is discharged through resistor R9 and after some time (depending on the capacitance of the capacitor and the resistance of the resistor) the voltage across it drops so much that the relay releases. Contacts K1.1 return to their original (shown in the diagram) position and open the generator power circuit.
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