Electronic Siren Circuit

Abstract

The invention is an electronic siren comprising in combination means for generating periodically occurring charging pulses at a selected one of a plurality of predetermined repetition rates, time-constant determining means coupled to the pulse generating means for generating a repeating voltage wave form in response to the charging pulses and means coupled to the time-constant determining means for generating a square wave signal having a frequency proportional to the instantaneous voltage of the voltage wave form. Coupled to the square wave generator is an output circuit which includes a first pair of transistors and first circuit means coupling the transistors to the square wave generator for driving the first pair of transistors individually and alternately into saturation in response to the aforementioned square wave signal. There are also provided a second pair of transistors and second circuit means coupling the second pair of transistors to the first pair of transistors for driving the second pair of transistors individually and alternately into saturation in synchronism with saturation of the first pair of transistors.

What is claimed is: 
     
       1. In an electronic siren the combination comprising: a. means for selectively generating periodically occurring charging pulses at one of a plurality of predetermined repetition rates,   b. time constant determining means coupled to said pulse generating means for generating a corresponding plurality of repeating voltage wave forms in response to said charging pulses,   c. means coupled to said wave form generating means for generating a square wave signal having a frequency proportional to the instantaneous voltage of said voltage wave form,   d. a power output amplifier circuit including 1. a first pair of .[.diffused base.]. transistors connected in a push-pull circuit configuration,   2. first circuit means selectively coupling said first pair of transistors to said square wave generator for driving said first transistors individually and alternately into saturation in response to said square wave signal,   3. a second pair of .[.diffused base.].  transistors connected in a push-pull emitter follower configuration, .Iadd.said second pair of transistors being diffused base transistors, .Iaddend.   4. second circuit means coupling said second pair of transistors to said first pair of transistors for driving said second pair of transistors individually and alternately into saturation in synchronism with saturation of respective ones of said first pair of transistors, and     e. impedance matching means for coupling said second pair of transistors to a sound reproducing device.   
     
     
       2. The combination of claim .[.2.]. .Iadd.1 .Iaddend.wherein said first circuit means includes means for applying said square wave signal to the bases of said first pair of transistors, said second circuit means is coupled to the bases of said second pair of transistors, said second circuit means includes an auto transformer having a pair of input terminals and a pair of output terminals, said first pair of transistors each having a similar one of their collector and emitter connected in common, and the other of their collector and emitter connected to said input terminals, respectively, said second pair of transistors having their bases connected individually to different ones of said output terminals. 
     
     
       3. The combination of claim 1 further comprising means for generating a first audio signal, said first circuit means further including first switch means for selectively connecting said power output circuit to one of said square wave generators and said audio signal means, means for electrically biasing the transistors of said first pair of transistors to their threshold of conductivity whereby said first circuit means renders said first pair of transistors individually and alternately conductive in proportion to said first audio signal. .[.4. The combination of claim 3 further comprising means for electrically biasing the transistors of said first pair of transistors to their threshold of conductivity, said first circuit means rendering said first pair of transistors individually and alternately conductive in proportion to said first and said second audio 
     
     
        signals in response thereto..]. 5. The combination of claim 3 wherein said second circuit means includes means for rendering said transistors of said second pair of transistors individually and alternately conductive in proportion to the degree of conductivity of said first pair of transistors when said output circuit is selectively connected to said audio signal 
     
     
        means. 6. The combination of claim 1 wherein said square wave generating means comprises an astable multivibrator circuit which includes a pair of switching transistors, said switching transistors each having a similar one of their collector and emitter connected in common, their bases coupled to said time constant determining means, and a pair of capacitors connecting the other of said collector and emitter of each said switching transistor to the base of the mutually opposite one of said switching transistors, the switching frequency of said multivibrator being 
     
     
        proportional to the voltage applied to said bases. 7. The combination of claim 6 wherein said multivibrator circuit includes an output circuit having a pulse-shaping means for increasing the switching speed of said 
     
     
        switching transistors. 8. The combination of claim 7 wherein said multivibrator further includes balancing means for rendering said square 
     
     
        wave symmetrical. 9. The combination of claim 8 wherein said balancing means includes a resistor and a potentiometer connected electrically in series with the collector-emitter circuit of one of said switching 
     
     
        transistors. 10. The combination of claim 9 wherein said pulse-shaping means is a capacitor connected electrically in series with the 
     
     
        collector-emitter circuit of the other of said switching transistors. 11. The combination of claim 1 wherein said first circuit means includes means for electrically isolating said power output circuit and said 
     
     
        multivibrator circuit. 12. The combination of claim 11 wherein said isolating means comprises a Darlington amplifier circuit which includes an 
     
     
        input terminal coupled to said output circuit. 13. The combination of claim .[.18.]. .Iadd.11 .Iaddend.further comprising second isolating means for electrically isolating said square wave generating means from said 
     
     
        time constant determining means. 14. The combination of claim 13 wherein said second isolating means includes an isolation transistor having a base, and a collector-emitter circuit, said base being connected to said wave form generating means, said collector-emitter circuit being coupled 
     
     
        to said square wave generating means. 15. The combination of claim 1 wherein said pulse generating means is a .[.second.]. multivibrator 
     
     
        oscillator. 16. The combination of claim 15 wherein said .[.second.]. multivibrator oscillator includes a plurality of frequency determining elements and .[.second.]. switch means for selectively connecting a predetermined one of said frequency determining elements into said oscillator circuit thereby determining the switching frequency of said 
     
     
        multivibrator. 17. The combination of claim 16 wherein said selecting 
     
     
        means includes a multiple pole switch. 18. The combination of claim 16 
     
     
        wherein said frequency determining elements are capacitors. 19. The combination of claim 1 further comprising means for selectively disabling said pulse generating means and means coupled to said time constant determining means for manually generating a plurality of charging pulses, said time constant determing means being responsive to said manually 
     
     
        generated pulses to generate one of said wave forms. 20. The combination of claim 14 further comprising means for coupling an auxiliary siren 
     
     
        circuit to said time constant determining means. 21. The combination of claim 20 wherein said auxiliary siren connecting means is connected to said time constant determining means, said second isolating means being connected between said auxiliary siren connecting means and said square 
     
     
        wave generator. 22. For use in an electronic siren capable of producing selectively, audio and siren signals, a power output amplifier circuit including a. a first pair of .[.diffused base.]. transistors connected in a push-pull amplifier circuit configuration having input and output circuits, means for selectively biasing said transistors to the threshold of conductivity whereby audio signals coupled to said input circuit renders said transistors alternately conductive in proportion to the amplitude thereof,   b. a second pair of .[.diffused base.]. transistors connected in a push-pull emitter-follower amplifier configuration having input and output circuits, .Iadd.said second pair of transistors being diffused base transistors, .Iaddend.means coupling the first-mentioned output circuit to the second-mentioned input circuit for driving said second pair of transistors alternately into saturation in synchronism with saturation of respective ones of said first pair of transistors,   c. impedance-matching means for coupling said second pair of transistors to a sound producing device, said impedance matching means having input and output circuits the input circuit of which being connected across the emitters of said second transistors, the last-mentioned input circuit   
     
     
        having an impedance appearing across said emitters. 23. The circuitry of claim 22 wherein said coupling means includes an auto transformer having a pair of input terminals and a pair of output terminals, said first pair of transistors each having a similar one of the collectors and emitters connected in common and the other connected to said input terminals, respectively, said second pair of transistors having the bases thereof connected respectively individually to different ones of said output 
     
     
        terminals. 24. The circuitry of claim 23 in which the emitters of said first transistors are connected in common and the collectors thereof are connected, respectively, to said input terminals, said impedance-matching means including a transformer having primary and secondary windings, the primary winding being connected between the emitters of the second transistors, a source of voltage connected between the center of said 
     
     
        primary winding and the collectors of said second transistors. 25. The circuitry of claim 24 including a square-wave generator and a source of audio signals selectively coupled to said input circuit of the first-mentioned amplifier and switch means for selecting which of said generator or source is applied to said first mentioned input circuit.