Electronics

Thursday, May 30, 2013

US police siren circuit using 555 timer

                               
The US police siren circuit presented in this schematic is an alarm circuit which produce the sound of the US police .
This US police siren schematic circuit is based on the 555 multivibrator . To built this US siren circuit we can use two 555 IC’s or one 556 IC which contain two 555 chips in one package .
Synchronously with the siren sound a lamp will flash . The siren circuit is capable to drive loads with greater than 1 A current consumption for one or more lamps or a powerful loudspeaker .
Both 555 IC’s timers are configured to operate as astable multivibrators.
The first timer is configured to supply a rectangular signal of about 2 Hz at pin 9. The lamp is switched on and off by way of power transistor . The second 555 is configured to supply a square wave at pin 5 that drives the loudspeaker. The loudspeaker of the siren must have a value between 8 and 32 ohms .
The voltage needed for this siren can be between 5 and 15 volts .


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