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High Performance Hee Haw Electronic Siren

2017-08-15 05:51  
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Electronic sirens are basically high-performance sound signal electronic amplifiers just like those in home sound systems. However, these sirens work with substantially higher outputs and specific demands are placed on them in terms ofdesired extreme reliability and different methods of their control.The oscillator based on IC2 is responsible for producing the sound. Its output is connected to the base of TRl,which amplifies it to drive the speaker. Resistor R4 is included in the circuit to limit the current through TRl to a safe and reasonable level. The oscillation frequency of IC2 is partially dependent on the values of R3 and C2. Another factor that governs the frequency of oscillation is the magnitude of voltage fed to pin 5 of IC2. If a voltage of varying magnitude is fed to pin 5, the internal circuitry of the IC is forced to reset at a different rate, which changes the frequency. IC1 is also connected as an oscillator,but it runs much slower than IC2: around 1 Hz. Each time theICtriggers, the voltage at pin 3 goes high. As pin 3 is connected to pin 5 ofIC2 , this forces IC2 to change its note. That produces the `hee-haw` sound of the siren.The oscillation frequency of IC2 is partially dependent on the values of R3and C2. Another factor that governs the frequency of oscillation is the magnitude of voltage fed to pin 5 of IC2.