Emergency Siren circuit Simulates Police

This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail.
The heart of the circuit is the two transistor flasher with frequency modulation applied to the base of the first transistor. When the pushbutton is depressed, the frequency of oscillation climbs to a peak and when the button is released, the frequency descends due to the rising and falling voltage on the 22 uF capacitor. The rate of change is determined by the capacitor value and the 100k resistor from the pushbutton. The oscillation eventually stops if the button is not depressed and the current consumption drops to a tiny level so no power switch is needed.

Read more original source:
http://www.techlib.com/electronics/noisemakers.html

This entry was posted on Sunday, June 22nd, 2008 at 12:42 pm and is filed under Audio - Alarm. You can follow any responses to this entry through the RSS 2.0 feed.