Dual tone siren. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators
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As a source of a powerful sound signal in modern security systems, as a rule, quite expensive piezo sirens are used. But a powerful sound emitter can also be built from publicly available elements.
Schematic diagram of a two-tone siren is shown in fig. 1. Acoustic radiator BA1 - low-resistance (Rн=4...8 Ohm), rather powerful (4...5 W) dynamic head, - is included in the diagonal of the bridge formed by transistors VT1... VT4. Two tone RC generators (DD1.2, DD3.2 and DD1.3, DD2.1) and one switching (DD1.1, DD3.1) generate an alarm signal. With such ratings in time-setting RC-chains, the frequencies of tone generators will be close to 1 kHz and 500 Hz, respectively, and their change will occur at a frequency of about 2 Hz.
Rice. 1. Two-tone "siren" (click to enlarge)
Other elements of the DD2 and DD3 microcircuits are included in the transistor control unit. If a low-level voltage (~0 V) is applied to the "Signal" input, then all transistors go into the closed state, and the generators turn off; if it is high (close to +Upit - siren supply voltage), then the switching generator is switched on and, depending on its phase, one of the tonal ones. And at the output of the DD2.2 element, a meander of one frequency or another appears.
In this mode, transistors VT1 ... VT4 open alternately in pairs - either VT1 and VT4, or VT2 and VT3. Since they operate in the key mode, the voltage amplitude at the load BA1 will be close to Upit-2Uke us, where Uke us is the saturation voltage of the transistor (in transistors KT972 and KT973 Uke us 1 V).
The frequencies of tone generators can, of course, be different: by changing the values of R5, C2 and R8, C3, you can "move" them over a very wide range. It is advisable to set one of the tone generators to the frequency of the mechanical resonance of the acoustic system (and both, if it has a two-peak resonance). By varying the values of R3 and C1, it is possible to change the rate of change of tonal bursts.
The current consumed by the "siren" in silent mode, Ipotr.dezh <2 uA. In the alarm mode, it depends on the supply voltage and load resistance: Icont.tr \u2d (Upit -XNUMXUke us) / Rn, where Icont.tr - in amperes, Upit - in volts, Rn - ohms.
The "siren" supply voltage may be higher than specified, but not higher than that allowed for microcircuits (for microcircuits of the K561 series Upit max = 15 V). In such cases, it is recommended to put transistors on good heat sinks and use dynamic heads with Rні8 Ohm.
If such or similar transistors (forming powerful complementary pairs and having a current gain h21e> 750) cannot be obtained, then the block of transistor switches can be made as shown in Fig. 2. Transistors of the KT315 (VT1, VT4) and KT361 (VT5, VT8) series can be with letter indices B, G, E.
Rice. 2. Output stage "siren" (option)
It is recommended to place the dynamic head, power source (for example, a 10NKN-3,5 battery or sealed acid battery), the electronic part of the siren in order to minimize losses in the connecting wires (with extended communications, their resistance can be comparable to Rn). In addition, placed in a strong metal case, fixed in a hard-to-reach place, such a siren will also be "criminal-resistant".
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