ELECTRONIC SIREN

ELECTRONIC SIREN

In this Circuit, the LM3909 is used in a simpłe electronic siren. When SI is closed, C2 begins to charge rapidly through Rl. When the charge on C2 reaches about 1 V, the oscillator starts. As the voltage across Cl increases toward +V, the oscil-lator’s output freąuency also increases. Releasing (opening) SI removes power from the Circuit. The oscillator continues to operate, with a de-cline in output volume and freąuency until Cl discharges to about the 1-V level.

Experiment with the siren Circuit by select-ing different R₁/C₂ combinations to obtain a de-sired rise and fali output. Change the value of C₁ to vary the oscillator’s freąuency. Keep the value of R₂ at or above 47 Q to protect the IC from drawing too much current.