Programmable electronic siren

Abstract

A dynamic loudspeaker is driven by chopped d.c. from the collector of a transistor. A free wheeling diode is connected in parallel with the speaker circuit to dissipate the inductive energy in the speaker voice coil when the transistor is turned off. The transistor is controlled by a voltage controlled oscillator which, under control of other elements, can be made to produce a wide variety of cyclically varying output signals for producing a wide range of sounds, tones and signals from the loudspeaker. This permits selection of a tone which differs sufficiently from the ambient noise to assure attracting attention. By the use of chopped d.c. to drive the speaker, the expense, weight and bulk of an impedance matching transformer is eliminated. A plurality of individually operable switches are provided for switching circuit elements in and out of circuit to modify wave shapes and alter sound output. Another group of individually operable switches mixes selected wave shapes to produce various compound waves and produce additional sound variations. One switch provides pitch control and another provides output volume control.

Dependencies are inferred from the claim text.