The working of this four siren sound generator is based around the operation of the UM3561 IC. here, the
oscillator generates the necessary clock pulse for the operation of the IC. The frequency of the oscillation
is determined by the resistor connected to pin 7 (OSC1) & pin 8 (OSC2) of the IC.
A 220KOhm resistor is connected across pin 7 & 8 to aquire the output. The output generated by the
UM3561 IC is not enough to drive the 8 Ohm loudspeaker. In order to amplify the output of the UM3561
IC, a BC547 transistor is used at Pin 3 (OUT) of the IC.