My proposed device here, we can say, almost out of the competition. First, it’s homemade. Secondly, made on the basis of a conventional PA speaker contains a minimum of parts and is able to present a strong enough audio signal, because the emitter is a speaker. Thirdly, the power of such a signalling device is supplied from an independent voltage source (battery). Fourth, the device does not consume energy in standby, it’s absolutely safe and can be used not only as a home call, but the sound indicator in the alarm system. The contact of a button, a reed switch or other running on the circuit the sensors may be located at a distance of 100 m from the alarm.
Circuit diagram homemade the call on the basis of the subscriber of the loudspeaker and the option of its use as security devices, as well as raznolikogo (Children — Adult) sound signaling the arrival of guests.
Due to the small number of parts makes no sense to produce printed circuit Board. Installation: hinged manner, familiar to all from school lessons of physics. As supports used in soldering speaker outputs, a transformer, a 68-kilomega potentiometer.
Volume control base speakerphone — R1 on the circuit diagram — performs the control function of the pitch of the generated signal, which is an optional extra. Switch (toggle switch, button or other pin connector) is placed in a convenient location at the entrance of the entrance section on the floor, apartment entrance doors.
As the transistor VT1 will fit any of a number of low-power germanium МП39 — МП42. Equally uncritical selection of the resistor R2 (and also R3 and R4 at the non-standard use case of the call): will fit most common VS, MLT, ULM with a rated power of 0.125 W or more. The condenser may be of any type (like working on a short reed switches, if the sound alarm will
work in the alarm system). The elements R1, T1, and BA 1 — from the PA speaker.
It happens that the call is correctly assembled when the power is connected is not running. Then you should swap the ends of one of the windings of the transformer T1. However, the lack of generation on the sound frequency may be a consequence of neconditionata of the transistor VT1. In this case you will have to replace it with another having higher gain.
If the range of adjustment of the pitch potentiometer R1 does not suit the owners, it is easy to change the selection of the capacitance of the capacitor C1. But the sound of this call depends on the voltage
the power that can be used, for example, raznoshennoy alarm systems in the protection of several objects, personalize the caller (“Children” “Adults”) by entering into the circuit (in series with a particular switch) low resistance resistor. To change the pitch of the call can also be judged on the degree of discharge power and time to change hooked galvanic element or battery are new. Just do not forget about polarity, because the transistor does not tolerate the pole reversal.
V. BESEDIN, Tyumen