Probably you happen to see this picture: all the appliances in the apartment turned off, and the meter disk rotates slowly. It turns out that the culprit door electric bell: its primary winding permanently connected to the network.
“M-K” already told about the design calls deprived of this drawback (e.g. in # 8 in 1972). But the trouble is, they don’t ring especially nice, and they do not have the circuit breaker, sound.
In its design the call, I took these shortcomings into consideration. Electronic device produces sounds resembling the Nightingale trill.
The scheme consists of two unsymmetrical multivibrators, collected on the transistors V1 — M3 (Fig. 1). The oscillation frequency of the first of them (V1, M3) is equal to 10 Hz and depends on the capacitance of the capacitors C1, C2 and resistors R4, R8. The second multivibrator (V2, V3) generates a signal with frequency of 2500 Hz. It is determined by capacity of C3, C4 and the resistance R7, R8.
If the call button long press, “Nightingale trill” is heard only 4, and then restarts after 15 seconds.
Fig. 1. Schematic diagram of the call.
Fig. 2. PCB-call with location details.
The volume of the signal does not depend on the position of the engine variable resistor R9: the call is heard even if it is disconnected from the radio transmission network.
The device in this configuration is almost not needed. If the second multivibrator runs erratically, between the base and the collector of transistor V2 is recommended to include the diode.
The duration of pauses between “songs” is determined by the capacitance of the capacitor C2 and resistances of the resistors R1, R8.
The circuit mounted on the circuit Board (Fig. 2) mounted in the housing of the loudspeaker broadcasting.
The device used the following parts: resistors MLT-0,25, the capacitors C50-6 (C1, C2) and KLS (C3, C4). Transistors have In≥40. Power source is battery “Krona” or, if size permits, two series-connected battery 3336L.
G. DOLL, Kiev
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