Schematics > Security and other sensors and detectors > Police Siren
Police Siren
This circuit produces a sound similar to the police siren.
It makes use of two 555 timer ICs used as astable multivibrators. The frequency
is controlled by the pin 5 of the IC.
The first IC (left) is wired to work around 1Hz. The 47uF capacitor is charged
and discharged periodically and the voltage across it gradually increases and
decreases periodically.
This varying voltage modulates the frequency of the 2nd IC. This process repeats
and what you hear is the sound remarkably similar to the police siren.
Two presets VR1 and VR2 are provided to vary the siren period of repetition and
the tone of the siren.
By varying VR1 you can set how fast the siren changes from high freq. to low
freq.
VR2 sets the siren frequency. Adjust VR1 and VR2 to suit your taste.
Title: Police Siren
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-01
Reads: 533
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