Pocket siren. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Security devices and object signaling
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This device is intended for those who are concerned about their safety. It can be useful for children, women and allows the owner to attract the attention of people around him to provide the necessary assistance. The circuit can also be used as part of a burglar alarm as an additional sound signaling device.
Rice. 3.20. Siren wiring diagram (click to enlarge)
The device can be easily placed in any pocket and, when turned on, creates a smoothly changing sound signal, similar to the sound of a police siren. The signal volume is enough to attract the attention of surrounding people within a radius of more than 50 meters.
The scheme of the device is shown in fig. 3.20. It consists of two coupled oscillators on the D1 chip. The frequency of the generator on the elements D1.4, D1.6 is changed by the field-effect transistor VT1, which is controlled by the generator (D1.1, D1.2) with a lower operating frequency.
As a sound source, a piezo emitter ZGI, ZP-22 or similar is used. To increase the sound volume, the emitter is connected to the T1 transformer. It can be taken from a small-sized radio receiver, using a winding with a large number of turns as a secondary, and connecting the primary (or part of it) according to the autotransformer circuit, as shown in the figure.
This inclusion of HF1 allows you to receive on it an alternating voltage of more than 100 V, which significantly increases the volume of the sound. Microswitch S1 type PD-9-2 or any small-sized one is used.
The circuit board layout can be used (with minor modifications) from the bird voice simulator circuit (see Section 6, Figure 6.1).
The design of the case can be anything, but the only requirement that it must satisfy is mechanical strength (withstand the impact when the device is dropped).
Publication: cxem.net
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