Piezo siren from SP-1. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Piezo siren from SP-1. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators

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The high price of branded piezo sirens, especially those with a built-in power source, prevents their widespread use in amateur radio practice. But you can make such a siren yourself. And if you supplement it with a switch of a special design, then it will find a special application for itself ...

Piezo siren at SP-1 (click to enlarge)

The basis of the siren is the piezoelectric element SP-1 (SP - piezoceramic siren). The sound pressure developed by it at an excitation voltage of 40 V can reach 110 dB. On fig. 88 shows a schematic diagram of an electronic converter that provides the mode of operation required for SP-1. Here VT1, T 1, etc. - a low-frequency generator, excited at a frequency depending on the reactance of the piezo emitter HA1 and the inductance of the step-up winding I of the transformer T1. The amplitude of the alternating voltage on the piezoelectric emitter is Uampl@UpitN1/N2, where Upit is the siren supply voltage, and N1 and N2 are the number of turns in the windings I and II. Acoustic radiation acquires an alarming character only after a special modulation of a monotonous signal. Here, this is done by an electronic manipulator - a transistor VT2 included in the power supply circuit of the generator. The frequency of its on-off depends on the constant R4C1 of the generator, made on the DD1 chip, and is equal to F@1/2R4·C1=5...6 Hz. Transformer T1 - B 4: 731.083 - output from the transistor receiver. Or similar to it with N1/N2=6...7 and output from the middle of the primary winding.

Chip DD1 - K561LE5 or K561LA7 - can be replaced by a similar one from the K 176 series. Transistors VT1 and VT2 must have a current gain of at least 100 and a saturation voltage Uke us <0,3 V. When replacing the KT3102E transistor with any other, you should have in mind that the voltage on its collector can reach 18 ... 20 V. All resistors of the "siren" are MLT 0,125. Capacitors: C1 - KM-6; C2 - oxide of suitable sizes, its capacity may be more than indicated. Diode VD1 - any silicon.

If the siren assembled without visible errors does not sound, the reason will most likely be in the wrong phasing of the transformer windings. The siren must be immediately turned off (the current consumed in this mode can be dangerous for transistors) and, by swapping the ends of one of the windings (1-3 or 4-5), turn it on again. You can experiment with resistors R1 and R2 (you even need a different type of transformer). But since they are regime, it is better to do this under the control of an oscilloscope. The power of the acoustic signal emitted by the siren to a very large extent depends on the size and configuration of its body, the presence of acoustic "sinuses" in it, on the place and method of attaching the piezoelectric emitter, etc. But all this is usually found out experimentally - acoustic calculations here can hardly be recommended.

Upit,B	Ipot, mA	Ueff, V
6	13,5	30
7	15,0	32
8	16,0	34
9	18,0	40

Piezo siren from SP-1
The appearance of the siren

We only note that monotonic radiation with its pronounced interference effects has its own characteristics.

Structurally, the siren can be made as shown in Fig. 89. Her. dimensions - 58x58x38 mm, weight - 95 g (with a power source - a battery of the "Korund" type). The case is glued from impact-resistant polystyrene 2...2,5 mm thick. Holes located on the periphery of the SP-1 holder are recommended to be sealed. Experience shows that this significantly increases the volume of the siren.

Table 15 shows the dependence of the current Iconsumed by the siren and the voltage on the piezo emitter Ueff (effective value) on the voltage of the power supply Upit.

Siren can work in a variety of devices and installations. Even as a doorbell. But its small size and weight make it possible to use it in an unusual security system.

To do this, you only need to insert the switch shown in Fig. 90. Here: 1 - normally closed contact pair from the relay; 2 - a check - a thin plate of an electrical insulator (getinaks, fiberglass, etc.), opening the contact pair 1; 3 - switch body; 4 - thrust (string, thin cable, etc.), extracting the pin from the contact pair.

Piezo siren from SP-1
Circuit breaker design

A piezo siren with a switch is placed inside a protected item - in a suitcase, in a fur coat pocket, etc. The rod is passed through a suitable or specially made hole and connected to a luggage rack, hanger, etc. When the stolen check is moved, it leaves the contact pair, the siren's power is turned on, and the thief with the object "screaming" in his hands becomes the center of attention of others.

See other articles Section Calls and audio simulators.

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