Simple megaphone with siren mode. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Calls and audio simulators
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Megaphones are useful in public speaking, organizing and directing group exercise and social events. It is very useful if the megaphone has a siren function, which allows you to call attention to the speaker with a sound signal.
A diagram of a simple megaphone based on the TBA810 chip is shown in the figure. It can be powered by a rechargeable or galvanic battery with a voltage of 7 ... 15 V. The output power is from 1 to 6 W, depending on the supply voltage and load resistance.
Rice. 1 (click to enlarge)
A preliminary microphone amplifier is built on the VT1 transistor and related components. Its voltage gain is approximately equal to the ratio of the resistances of resistors R7 and R8. The collector current of transistor VT1 is set to approximately 0,5 mA by selecting resistor R4. Jumper S1 is installed only if the BM1 microphone needs power. When switch SA2 is closed, the signal from the collector of transistor VT1 is fed to the output power amplifier. It is built on the UMZCH TBA810 (DA2) microcircuit, which has a small current consumption (about 12 mA at a supply voltage of 14,4 V) and delivers about 6 W of power at this voltage to a load with a resistance of 4 ohms. Variable resistor R11 adjust the volume of the signal coming from the microphone.
On the chip element DD1.4, capacitor C10 and resistor R13, a rectangular pulse generator with a frequency of about 1000 Hz is built. When the SB1 button is pressed, its pulses are also fed to the input of the final amplifier. A single tone siren sounds. Its volume is set by a tuning resistor R15.
Element DD1.1 serves as a pulse generator with a frequency of 0,5 Hz. They are fed to the inputs of the elements DD1.2 (directly) and DD1.3 (through an inverter on the transistor VT2), turning on the generators assembled on these elements in turn. The first generates pulses with a frequency of 2000 Hz, and the second - 500 Hz. Their output signals are summed using resistors R14 and R16. When the SB2 button is pressed, a signal of two alternating tones is fed to the input of the final amplifier. Trimmer resistor R17 set its volume.
The power of the BA1 dynamic head must be at least 6 watts. The SA1 switch turns the megaphone on and off. The BL-L532URC LED, which indicates power on, can be replaced with another of a suitable glow color and sufficient brightness at a current of 1,2 mA.
Author: P. Petrov
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