Unenviable situation: come visit, but to notify the owners of this difficult - when the apartments started to recall, or fortress, or prison with armored bulletproof input doors in the hallways, on floors and barred Windows.
To solve the "signal information" problem can partly electric bells. But most of them need domestic 220 volt network (and consumption power is available and when "the tram's trill, and in standby mode) that is not a safe practice. Look at this background, electronic music calls, but they are not cheap.
My proposed device here, we can say, almost out of competition. First, it's homemade. Secondly, is made on the basis of the usual PA loudspeaker, contains a minimum of parts and is able to apply a strong enough audio signal, because the radiator speaker. Thirdly, the power of such a detector is supplied from an independent low-voltage source (batteries). Fourth, the device does not consume energy in the mode wait, is absolutely safe and can be used not only as apartment ringtone, but the sound indicator in the alarm system. And the contact of a button, reed switch or other operating-closure sensors can located at a distance of 100 m from the sound projector.
A circuit diagram of an improvised call based on subscriber loudspeaker option and its use as a security device, and also razmotannogo ("Children" - "Adult") the audible alarm of the parish guests.
Due to the small number of parts makes no sense to manufacture the printed circuit Board. Installation is hinged manner, familiar to all from school physics lessons. In the bearing supports are used when soldering the speaker outputs, transformer, 68-kilomega potentiometer.
Volume control base speakerphone - R1 on schematic wiring diagram - performs the function of pitch generated signal, which is optional. Switch (toggle switch, button, or other connector) is placed in a convenient location at the entrance to the staircase, the section on each floor, apartment entrance doors.
As transistor VT1 will fit any of the number of low-power germanium MP39 - MP42. Equally uncritical choice of the resistor R2 and also R3 and R4 to the non-standard a use case of a call): the most common Sun, MLT, ULM with a rated power of 0.125 W and more. The condenser may be of any type (like working on the circuit reed switches, if a given audio alerter have to work in the alarm system). The elements R1, T1 and BA1 from PA speaker.
It happens that correctly assembled the call when the power is not working. Then you should swap the ends of one winding of the transformer T1. However the lack of generation on sound frequency may be a consequence of the neconditionate of the transistor VT1. In this case you have to replace it with another, having higher gain.
If the tuning range of the pitch potentiometer R1 is not satisfied with the hosts, it is easy to change the selection of the capacitance of the capacitor C1. But the sound of this call depends on the voltage that can be used, for example, raznochinnoj signal when the protection of multiple objects, personification the caller ("Children" - "Adult") by entering into the circuit (in series with one or another switch) low-resistance resistor. By changing the pitch of a call can also to judge the degree of discharge power and time to change hooked galvanic cell or battery with a new one. But we should not forget with the correct polarity, because the transistor does not tolerate perepolyusovka.
Author: Vladimir Besedin