US3889256A - Automatic control for audible electronic warning system - Google Patents

Abstract

This invention is an electronic siren producing a siren sound having a sound wave produced on a slowly rising and falling frequency. A major cycle is pulsed at intervals with variations in frequency. The variations in each major cycle represent minor cycles. The invention utilizes an electronic circuit to effect such major and minor frequency cycles with existing speaker equipment to project the sound.

Description

United States Patent Cieslak et al.

[ June 10, 1975 [54] AUTOMATIC CONTROL FOR AUDIBLE 3,579,233 5/1971 Raschkc 340/384 E ELECTRONIC WARNING SYSTEM 3,587,094 6/1971 Scott 340/384 E [75] Inventors: Richard F. Cieslak, Algonquin; John 1 v. Balding, Palatine, both of I11. j y PIttSB M w n tto ,A 1,0 ann, rown, c i [73] Assignee: Industrial Electronics Service Co., & zg r [rm rams Schaumburg, Ill.

[22] Filed: July 9, 1973 [57] ABSTRACT [21] Appl. No.: 377,644

This invention is an electronic siren producing a siren [52] U S Cl 340,384 E. 340/384 R sound having a sound wave produced on a slowly ris- [51] Gosh 3/00 ing and falling frequency. A major cycle is pulsed at [58] Fie'ld 331/47 intervals with variations in frequency. The variations 84/124 1 in each major cycle represent minor cycles. The invention utilizes an electronic circuit to effect such major and minor frequency cycles with existing [56] EEZF E SZ Q speaker equipment to project the sound.

2,847,663 8/1958 Stoddard 340/384E 6 Claims, 3 Drawing Figures l2 I3 l6 I71 IE IS I MAJOR SHAPING ECCLES l i TIMING JORDAN AUDIO OSCILLATOR NETWORK MODULATOR a SWEEP AMPLIFIER OSCILLATOR SPEAKER VARIABLE 25 /IO 20 PZCZE $335K d s i l/6:1 m H'VOLTAGE SIREN oscILLA'rpR SOURCE SWITCH IISHEET PATENTEDJUH 10 1975 we 200mm z m2 E.

m w m OON ZH NI XONBFIOEIHA BACKGROUND OF THE INVENTION The present invention is directed to electrical sirens and particularly to sirens of the type which may be used with emergency vehicles.

' Sirens commonly in use on emergency vehicles are of several types, i.e., as one utilizing a slowly rising and falling sound with a single or repetitive cycle. one using an alternating high and low frequency of sound or one using a slowly rising and falling sound frequency with minor sound frequency variations occurring during each cycle of the rising and falling sound. In the latter class of sirens, the sound has been produced by mechanical means. The first two types of sound producing sirens have heretofore been reproduced mechanically and electronically through use of motors or electrical amplifiers but, as far as is known, the third class has not heretofore been produced electronically. The mechanically produced siren noise has some desirable qualities not found in electronically produced siren sounds I which may be attributed to purely mechanical noises resulting from the sound producing apparatus. Mechanically driven baffling is used with mechanical sirens to create a minor pulsing of the siren sound during each cycle of rising and falling frequency of the sound.

SUMMARY OF THE INVENTION Electronically produced siren sounds have the advantages that sound emitting speakers of the siren may be located at various points in an emergency vehicle so that the sound direction may be predetermined. Electronically produced siren noises have the further advantage of utilizing combined or existing amplifying apparatus in an emergency vehicle thus reducing electrical power requirements in such vehicles. For example, the speakers used for producing a siren sound in the vehicle may also be used for a public address system.

OBJECTS OF THE INVENTION With the foregoing in mind, the present invention has for its major purposes to provide an electronically produced siren sound which closely simulates the mechanically produced siren sound above mentioned and which produces a slowly rising and falling sound frequency with variations in the frequency during ,each cycle of rising and falling sound, and to enable use of such electronically produced sound with existing speaker facilities of emergency vehicles, while at the same time arranging simple and effective circuits to attain these ends at relatively low cost of manufacture and installation.

DESCRIPTION OF THE DRAWINGS These and other purposes will appear from time to time in the course of the ensuing specification and claims when taken with the accompanying drawings, in which:

FIG. 1 is a block diagram of an electronic siren system in accordance with the present invention;

FIG. 2 is a schematic wiring diagram of the siren system showing the electrical relationship of all of the elements indicated in FIG. 1; and

FIG. 3 is a sound wave diagram.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the drawings, the several elements of the siren system include avoltage source 10. a voltage regulator 11, amajor timing oscillator 12, ashaping network 13, which supplies a variablepulse rate oscillator 14. A second shaping network takes the frequency supplied by theoscillator 14 and supplies it to amodulator 16, which mixes the output from theshaping network 15 with the output from theshaping network 13 and supplies this mixed frequency to asweep oscillator 17.Oscillator 17 suppliesaudio amplifier 18 for aspeaker 19. Aswitch 20 controls the siren. Thesweep oscillator 17 is powered from the voltage source I1 and is controlled by a bias voltage from modulator I6.

The sound generated by this electronic system is on a rising and falling frequency ranging from a peak frequency to a low frequency, requiring a time interval to reach the peak frequency and approximately the same interval to fall back to the low frequency. This varying frequency comprises a major cycle but is pulsed at a continuously varying rate and at peak frequency the pulse rate is at a maximum. Each pulse varies in frequency depending upon whether the major cycle is near the high or the low end and each pulse comprises a minor cycle. This variably pulsed sound. as generated by this system, is obtained through the circuitry illustrated in more detail in FIG. 2. This sound is shown diagrammatically in FIG. 3. As an example, the basic sound may be a rising and falling frequency ranging from 400 hertz to 1600 hertz. The sound takes approximately 3 to 5 seconds to reach the peak of 1600 hertz and the same time to fall back to the minimum. This is referred to herein as a major cycle. This varying frequency is then pulsed" at a continuously varying rate. Near or at peak frequency, the pulse rate is at a maximum (approximately 200 cpm). These pulses shall be referred to as minor cycles. Each minor pulse varies in frequency approximately to ZOOHZ and in length approximately 0.3 to 0.6 seconds, depending on whether the major cycle is near the high or low end.

The sweep oscillator varies in output frequency with the bias voltage frommodulator 16 so that as the bias voltage increases the output frequency of the oscillator also increases and when the bias voltage decreases the output frequency also decreases. Themajor timing oscillator 12 operates essentially like a switch, alternately turning on for a certain time period, as for example 3 to 5 seconds and then off for substantially the same period of time. Theshaping network 13 functions to change the voltage switched on and off by theoscillator 12 to a slowly rising and falling voltage wave form similar to a sine wave. It converts the square wave form of approximately 3 5 seconds duration fromoscillator 12 to a repetitive approximate sine wave of approximately 6 to 10 seconds duration. This voltage wave form provides a variable bias voltage for the sweep oscillator so that the output of the oscillator is a cyclically varying frequency of the same duration, i.e., approximately 6 to 10 seconds. This, in turn, provides a cyclically varying sound in the audio speaker of the same duration as illustrated in FIG. 3. The variablepulse rate oscillator 14 is supplied with the alternately rising and falling voltage from theshaping network 13 and varies its pulse rate proportionately, so that, as the voltage increases, the pulse rate also increases and when the voltage decreases the pulse rate also decreases. This vary- 1 regulator circuit 11 includes aswitch 25 and, when this switch is closed, positive voltage is applied from battery to the voltage regulator circuit. Thediode 26, with thecondenser 27 function as a filter while thetransistor 28,resistor 29, diode 30 and condenser 31 function as a series regulator. Two D.C. supply voltages are made available from this voltage regulator circuit. A filtered voltage supplies theamplifier 18 and a transistor amplifier supply inshaping network 13 for modulator l6 and variablepulse rate oscillator 14. The regulated voltage provides power foroscillator 12, variable rate oscillator l4 andsweep oscillator 17.

The majortiming oscillator circuit 12 is controlled by the on-offsiren switch 20. When this switch is closed the regulated positive voltage from the regulator 11 is continuously applied to the timing oscillator. Theresistors 32 and 33 and thecondenser 34 form a timing circuit inconjunction with thetimer 35.Timer 35 is a known form of timer for periodically dischargingcondenser 34. Thecondenser 34 is charged through theresistors 32 and 33 until the regulated voltage is reached at theconnection 36 on the timer, whereupon thecondenser 34 discharges through theresistor 33 into the timer at connection 37 until the voltage at theconnection 36 drops to approximately one-third of the regulated voltage and at this point thecondenser 34 again starts to charge and this cycle repeats continuously so long as the siren control switch is closed. The output of thetimer 35 at theconnection 38 represents a square wave form, as indicated, which switches from the high voltage to the low voltage, i.e., from the regulated voltage to ground, through the connection 39. The square wave is of approximately 3 to 5 seconds duration.

Theshaping network 13 includes adiode 40,resistances 41 and 42 and thecondenser 43. When the output of thetimer 35 through theconnection 38 is at the high, or regulated voltage, thediode 40 is biased on and thecondenser 43 charges through theparallel resistors 41 and 42. When the timer output throughconnection 38 is at the low voltage, diode 44 is biased off so that thecondenser 43 discharges through theresistor 42. Thus, there is provided at the base of transistor 45 a slowly rising and falling wave form wherein the duration is determined by the R-C time constant of thevariable resistance 33 and thecondenser 34 in the majortiming oscillator circuit 12.Diodes 44 and 46, andresistors 47, 48 and 49, are used to provide smooth starting and termination of the rising and falling voltage. The collector oftransistor 45 receives power from the filtered source of the regulator 11. Thetransistor 45 amplifies the current of the rising and falling wave form and applies it to the resistor 50 of the variable pulserate oscillator circuit 14 and to theresistor 51 of themodulator circuit 16.

I In the variable pulse rate oscillator circuit 14 aprogrammable unijunction transistor 60 is used.Condenser 61 is charged through theresistances 50 and 62. When charged, the voltage at theanode 63 oftransistor 60 increases until it reaches approximately of the voltage at the gate 64of the transistor. At thispoint transistor 60 turns on and discharges thecondenser 61 through thecathode 65 oftransistor 60 andresistor 66. As the voltage applied to the resistor 50 rises and falls, the charge time of thecondenser 61 accelerates and slows down, respectively, so that thetransistor 60 pulses at a varying rate. Each time the transistor pulses, a bistable multivibrator, comprised oftransistors 67 and 68,resistors 69, 70, 71 and 72, andcondensers 73 and 74, is energized. This provides a square wave of varying rate or duration at the collector oftransistor 68. This wave is cyclic in nature and of a much shorter time duration than the wave form fromnetwork 13. Also, the range of the variation in voltage occurring during the wave is much smaller than the range of voltage variation produced in the major wave.

Theshaping network 15 shapes the varying minor square wave from thetransistor 68 of the variable pulserate oscillator circuit 14, into a wave form which is similar to a triangular wave, at the junction on theresistor 75 andcondenser 76 and then reduces it in amplitude through a voltage divider formed by resistors 77 and 78.

The shaped wave from the majortiming oscillator circuit 12 and theshaping network 13 is applied to theresistor 51 of themodulator circuit 16 while the varying shaped wave from the variable pulserate oscillator circuit 14 and shapingnetwork 15 is applied to the cathode of thediode 79 of the modulator circuit. The resultant wave form at the junction of theresistor 51 and thediode 79 comprises essentially the minor varying wave from shapingnetwork 15 imposed on the major timing wave from shapingnetwork 13.

The mixed voltage wave form from themodulator circuit 16 is applied to the center tap of aresistor 80 in thesweep oscillator circuit 17, where it functions as a bias voltage for thetransistors 81 and 82. The output of the sweep oscillator at the collector of the transistor 82 increases in frequency as the bias voltage increases so that, as the slowly rising and falling variable pulsing wave form is applied to the sweep oscillator, the output frequency slowly rises and falls in synchronism with the rising and falling wave form fromnetwork 13 in synchronism with the minor wave form from shapingnetwork 15 while continuously pulsing at a varying rate. The pulses occur most rapidly at the highest frequency and occur most slowly at the lowest frequency.

The audio frequency output of thesweep oscillator 17 is then amplified by means of one or more audio amplifiers-l8, the circuitry of which, as shown, is generally typical of amplifiers of this type, and used to drive one ormore speakers 19 whereby to project a slowly rising and falling variably pulsing sound continuously while turned on. The frequency range of the output fromoscillator 17 corresponds in extent to the frequency range of the sound produced.

This electronic siren system has particular application to vehicles where the voltage source may be on the order of twelve volts, as provided in the usual automotive electrical system, but the principles of the system may be utilized with other voltages and in other installations where the location may be fixed. as distinguished from a moving vehicle.

It should be understood that voltage regulator cir cuits, timing oscillator circuits, wave shaping circuits, variable pulse rate oscillator circuits. sweep oscillator circuits. and audio amplifier circuits are known individually to the art but not in the combination or for the purpose herein described.

FINAL SUMMARY From the foregoing, it will be seen that an electronic siren system has been provided wherein an audio section of the electronic circuitry produces a slowly rising and falling variably pulsed sound level in accordance with frequencies developed in a basic electronic circuit. As the major sound frequency increases during the cycle of sound. minor variations in pitch occur. The occurrence of these minor variations becomes more rapid as the major sound frequency increase and less rapid as the major sound frequency decreases. This provides a simulation of the pulsing of the mechanically driven sirens where the pulsing is produced by mechanically driven baffling, the actuation of which reoccurs at a rate corresponding to the variable rotating speed of the siren drive.

.l claim:

1. An electronic siren including an audio speaker and an amplifier for producing sound at continual maximum audio output from said speaker in response to frequency variations transmitted to said amplifier, including frequency responsive amplifying means for an audio speaker. a voltage controlled sweep oscillator circuit for supplying a variable frequency to said amplifying means to provide frequencies distinguished from ambient sounds, modulating means for supplying a variable control voltage to said oscillator circuit. a timing oscillator circuit, said timing oscillator circuit including variable and settable means for supplying a pulsating voltage, a shaping network for changing the pulsating voltage of said oscillator circuit into a slowly rising and falling voltage which repeats in a cyclic manner, a variable rate pulse oscillator controlled by the output of said shaping network, a second shaping network for shaping the output of said variable rate pulse oscillator circuit means for imposing a varying cyclic voltage from said second shaping network on the voltage wave form supplied by said first shaping network in said modulating means to thereby produce a number of periodically rising and falling minor voltage variation on the main voltage wave supplied to said sweep oscillator circuit to thereby produce an amplifier control frequency having the characteristic of a cyclically recurring, slowly rising and falling main frequency of sound occurring over a preselected interval of time and a number of rising and falling minor frequencies occurring within said major frequency variation during each cycle of said main frequency while it is at maximum continual level.

2. An electronic siren system having an audio section projecting a square form sound wave at continual maximum audio output, electronic means for generating said sound wave of square form and slowly rising and falling frequency on a major cycle different from that of predominant ambient sound, and electronic means to pulse said major cycle and generate minor cycles to produce variable frequencies in said sound wave. said audio output being varied in rate and direction of frequency change represented by said minor cycles to change the frequency rate while it is at maximum continual level whereby to simulate a changing audio level.

3. An electronic siren system as set forth inclaim 2 wherein said means for generating said sound wave includes an electronic circuit. and said means to pulse said major cycle includes a variable rate pulse oscillator in said circuit.

4. An electronic siren system as set forth inclaim 3 wherein said electronic circuit includes a shaping network imposed on said major cycle, and a shaping metwork imposed on said minor cycles.

5. An electronic siren system as set forth inclaim 3 wherein said electronic circuit includes a timing oscillator for applying a variable frequency to said sound wave.

6. An electronic siren system as set forth inclaim 5 wherein said electronic circuit includes a shaping network imposed on said major cycle, and a shaping network imposed on said minor cycles.

Claims (6)

1. An electronic siren including an audio speaker and an amplifier for producing sound at continual maximum audio output from said speaker in response to frequency variations transmitted to said amplifier, including frequency respOnsive amplifying means for an audio speaker, a voltage controlled sweep oscillator circuit for supplying a variable frequency to said amplifying means to provide frequencies distinguished from ambient sounds, modulating means for supplying a variable control voltage to said oscillator circuit, a timing oscillator circuit, said timing oscillator circuit including variable and settable means for supplying a pulsating voltage, a shaping network for changing the pulsating voltage of said oscillator circuit into a slowly rising and falling voltage which repeats in a cyclic manner, a variable rate pulse oscillator controlled by the output of said shaping network, a second shaping network for shaping the output of said variable rate pulse oscillator circuit means for imposing a varying cyclic voltage from said second shaping network on the voltage wave form supplied by said first shaping network in said modulating means to thereby produce a number of periodically rising and falling minor voltage variation on the main voltage wave supplied to said sweep oscillator circuit to thereby produce an amplifier control frequency having the characteristic of a cyclically recurring, slowly rising and falling main frequency of sound occurring over a preselected interval of time and a number of rising and falling minor frequencies occurring within said major frequency variation during each cycle of said main frequency while it is at maximum continual level.

2. An electronic siren system having an audio section projecting a square form sound wave at continual maximum audio output, electronic means for generating said sound wave of square form and slowly rising and falling frequency on a major cycle different from that of predominant ambient sound, and electronic means to pulse said major cycle and generate minor cycles to produce variable frequencies in said sound wave, said audio output being varied in rate and direction of frequency change represented by said minor cycles to change the frequency rate while it is at maximum continual level whereby to simulate a changing audio level.

3. An electronic siren system as set forth in claim 2 wherein said means for generating said sound wave includes an electronic circuit, and said means to pulse said major cycle includes a variable rate pulse oscillator in said circuit.

4. An electronic siren system as set forth in claim 3 wherein said electronic circuit includes a shaping network imposed on said major cycle, and a shaping metwork imposed on said minor cycles.

5. An electronic siren system as set forth in claim 3 wherein said electronic circuit includes a timing oscillator for applying a variable frequency to said sound wave.

6. An electronic siren system as set forth in claim 5 wherein said electronic circuit includes a shaping network imposed on said major cycle, and a shaping network imposed on said minor cycles.

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