Posted on May 3, 2012

The wailing sound of a siren is generated by a VFO consisting of Q1 and Q2. Capacitor C2 provides the feedback for the oscillator. The frequency of the oscillator is varied by the voltage applied to the base of Q1 through R3. When switch S1 is closed, capacitor Cl charges, thus increasing the oscillator frequency. When S1 is released, capacitor {;1 discharges, and the oscillator frequency decreases.

Click here to download the full size of the above Circuit.

Capacitor C3limits the maximum oscillator frequency. The average battery current drain is about 15 mA.

Leave Comment

characters left:

New Circuits



Popular Circuits

Automatic Tr Switch Circuit
Geiger Counter
McCoy Mighty Midget Transmitter
high resistance voltmeter circuit diagram
89 S10 Starter wiring Snafu
High voltage (120V), converting familiar fast (120V Shu us) power MOSFET Amplifier circuit
SH-803R produced by high-power holiday lights
Long timed circuit diagram LM307N CA3094
Blackout emergency lights 4