A sound siren is used in various places and for a wide variety of purposes to alert you to something. It can be adapted to some security system, built into a toy, taken as a doorbell or something else. Having collected this simple monophonic siren, we get a loud and unpleasant sound, just in order to quickly respond to the notification.
A simple circuit diagram of a siren with a few details is waiting for you in the figure above. Conditionally, the circuit diagram can be divided into two parts: a multivibrator - a low-frequency amplifier. A multivibrator is committed to generating a signal of a certain frequency, and the amplifier, in turn, amplifies it. As a result, a loud sound with oscillations of about 2000 Hz is obtained.
Our multivibrator generates pulses by quickly opening / closing the BC547 transistors. The frequency is mainly related to the capacitance values of the capacitors and partly from the base resistors and the transistors themselves. In the circuit, the standard capacitance C1 and C2 = 10 nF and 22 nF, with a variation of these values, the tonality of the electric siren is corrected. You can get from the collector of any of the transistors (VT1 / VT2). In this device, the signal goes through the resistor further to the ULF cascade. The amplifier is based on two very common bipolar transistors BC547 and BD137.
Here are some computing options for a multivibrator. The frequency is approximately 959.442 Hz (the multimeter shows on the collector of the generator made 1-1.1 kHz), duty cycle S = 1.45, period T = 0.000104. This information may differ depending on the transistors used, other deviations in the characteristics of the radio components ... Almost everything affects the sound frequency. The current that is taken from the power source of the circuit can reach up to 0.5 Amperes, at 12 Volts.
Proteus circuit and board (file and):
Three-dimensional board in:
The NPN transistor from the low-frequency amplifier will heat up when the siren is activated, so we put it on the heat sink, I use a powerful and large C5803.
Now about replacing some parts. Here you can replace a lot of things, for example, we take almost any (NPN) KT315, BC548 and KT3102 transistors in the gene - all of them will work perfectly. An analogue of BC327 in this circuit will be BC558 / BC557 / CT3107. The BD139 is replaced generally like the same power or more.The capacitance of the capacitors will change the frequency, there is also a great choice, experimenting we select the preferred sound. Resistors may vary slightly, but remember that in the first part of the circuit the resistance R1 and R4 should be less than R2, R4.
We reproduce the sound of a siren on any speaker that is, R coils equal to 8-25 Ohms. I tried with the most different ones from both the radio and the home landline phone. Also try to test a piezoelectric element as a sound emitter, we must attach a resonator to it (you can use a case).
Very quiet siren? Not a problem! We take a ready ULF, for example, some kind of tdashka (the digital audio). Their variety is amazing, from small chips in DIP-8 at 1 Watt to large ones with a power of more than 100 watts. I would advise taking something mediocre, TDA2003 (up to 10W) or TDA2030 (up to 18 watts). Do not forget to watch what kind of food is needed for one or another "power amplifier" of the sound sound.
Appearance of the siren assembled by hinged installation:
Power supply from 6 to 12 Volts (with a large one it also functions perfectly). Output power up to five watts. When using accumulators / batteries, we get an autonomous siren that can work without mains voltage. If we give power from 220V, then we take a ready-made power supply or remake charging for the phone by replacing the zener diode with the desired voltage.