US3613093A

US3613093A - Surveillance system with improved detecting network

Info

Publication number: US3613093A
Application number: US861959A
Authority: US
Inventors: David Woodward Reynolds; Donald George Hang
Original assignee: POSTMASTER GENERAL USA
Current assignee: POSTMASTER GENERAL USA
Priority date: 1969-09-29
Filing date: 1969-09-29
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12

Abstract

This invention relates to a surveillance system utilizing a telephone line not only for transmitting an alarm signal between an area under surveillance and a central monitoring station but also for supplying the power necessary for the operation of the system. In the operation of one embodiment of this system, electrical signals are generated by a pickup transducer in response to the detection of an intrusion into the area under surveillance, are amplified, and are supplied to a detecting network. After insuring that the signals received are the result of an actual intrusion and not the result of some extraneous noise, the detecting network is operative to trigger an alarm circuit whereby an alarm signal is transmitted via a telephone line to a central monitoring station.

Description

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[72] Inventors David Woodward Reynolds 3,241,069 3/1966 Garfield 328/127 X Relay; 3,276,006 9/1966 Hansen 340/261 e Donald George Hang, Silver Spring, both of 3,378,829 4/ 1968 Alafi et a1. 340/416 Md. 3,434, 164 3/1969 Forbes 340/258 [21] Appl. No. 861,959 3,461,241 8/1969 Menke 179/5 [22] Filed Sept. 29, 1969 r 1 3,487,396 12/1969 Perelman 340/261 [45] Patented Oct. 12, 1971 73 Assignee The United States of America as 5227" Caldwell man! ExammerPerry Palen represented by the Postmaster General Attorneys-T. Hayward Brown and Joseph A. Hill [54] SURVEILLANCE SYSTEM WITH IMPROVED I DETECTING NETWORK ADS'I'RACT: This invention relates to a surveillance system 3 Claims, 1 Drawing Fig. utilizing a telephone lme not only for transmitting an alarm signal between an area under surveillance and a central mom- U-stoying tation but also for necessary for 179/5 328/127, 328/171, 340/261 the operation of the system. ln tiie operation of one embodi- [51] Int. Cl ..G08b 13/00 mem of this System, electrical Signals are generated by a {50] Field of Search 340/261, pickup transducer in response to the detection f an intrusion 258 R416; 179/5; 328/127- 171 into the area under surveillance, are amplified, and are supplied to a detecting network. After insuring that the signals [56] References cued received are the result of an actual intrusion and not the result UNITED STATES PATENTS of some extraneous noise, the detecting network is operative 3,134,970 5/1964 Kelly et al..... 340/261 to trigger an alarm circuit whereby an alarm signal is trans- 3,231,823 1/1966 Garfield et a1. 328/127 X mitted via a telephone line to a central monitoring station.

TO MON lTOR STATION SURVEILLANCE SYSTEM WITH IMPROVED DETECTING NETWORK BACKGROUND OF THE INVENTION ment as much as possible so as to reduce the overall cost of such a system. 7

One method of surveillance has been to install a radio I bug transmitter which picks up audio sounds in the protected area and to have a receiver tuned to the transmitter frequency continuously monitored at the central station. While sucha system does achieve a desirable feature of not making an intruder aware of the fact that he has been detected, such a system may be undesirable since it may require the continuous monitoring of the receiver at the central station. Furthermore, such a system may be limited by relevant communications laws, as for example by the number or range of frequencies available for such operations.

Still other methods of surveillance, while utilizing a telephone line for the transmission of an alarm signal, merely use the lines for that purpose, thus requiring a separate source of electrical power for the operation of the system.

The surveillance system of this invention is especially adapted for use on the type of telephone line commonly referred to as a private line. That is, a telephone line of the type in which the mere picking up of the receiver at one end automatically causes the ringing of a telephone at the opposite end. Such systems are well known and are commonly found in such places as airports, hotels, and the like.

Accordingly, one object of this invention is to provide improved means for maintaining the continuous surveillance over an area to be protected which does not require continu' ous monitoring by an operator at a central station.

Another object of this invention is to provide an improved surveillance system which permits the detection of an intrusion into an area being protected without making the intruder aware that he has been detected.

Still another object of this invention is to provide an improved surveillance system which utilizes a telephone line as a means for maintaining surveillance over an area to be protected.

Still another object of this invention is to provide an improved surveillance system which utilizes a telephone line not only in the transmission of an alarm signal to a central monitoring station but also as a source of power for the operation of the system. 7

SUMMARY OF THE lNVENTlON ln a preferred embodiment of the continuous surveillance system of this invention, an acoustical transducer is used to detect the presence of an intrusion into an area being protected. Electric signals are generated by the transducer in response to sounds generated in an area to be protected and are supplied to an amplifying circuit. The output from the amplifier circuit is supplied to a detecting network which controls the application of an alarm circuit onto a private telephone line. The detecting network includes an integrating and limiting circuit for insuring that the signals received from the trans- BRlEF DESCRIPTION or THE DRAWING The sole FIGURE is a schematic diagram of the circuit of a preferred embodiment of this invention.

,DESCRIPTlON OF THE PREFERRED EMBODIMENT Referring now to the drawing, there is shown a schematic diagram in which lines b-] and L-2 are respectively the power leads froma "private" telephone line. These lines provide all of the electrical power necessary for the operation of the system of this invention. A capacitor C-8 is connected between the leads and acts as a RF bypass to prevent stray RF (from nearby radio transmitters or the like) from causing a false alarm. The telephone line L-l is connected to one side of a stabilizing capacitor C4 through a zener diode D-2 and a resistor R-23. The telephone line L-2 is connected to the other side of capacitor C-l through an "on-oft" switch 8-1. The zener diode D-2 drops the basic 48 volt DC telephone voltage to 24 volts. However, if the telephone line is a 24 volt line, then the zener diode D-23 should instead be jumpered out. Thus, as shown in the drawing, L-l is the positive line while L-2 is the negative" line. The presence of the resistor R-Z provides a time delay RC circuit with C-l to permit a person to activate the network, as by closing the on-oft" switch 5-! and still have time to leave the room without setting off the alarm by any noise in his leaving. Furthermore, this same RC network acts as a power-supply filter to prevent extraneous telephone line noises from setting off the alarm.

Transducer means are provided for generating or producing electrical signals in response to the detection of an intrusion into the area being kept under surveillance. in this instance, it is desired to utilize a transducer which is sensitive to certain noises from an intrusion or intruder, such as the hissing of an acetylene torch or sharp sounds from a tool, to activate the alarm. Thus, an acoustical transducer means M is utilized and may comprise a microphone with uitably designed frequency response. However, it is not the intention of this invention to be limited to such a transducer and any suitable transducer may be utilized. As is shown in the FIGURE, one side of the microphone M is connected to the negative line L-2 and the other side is connected through a DC blocking capacitor C-2 to the input of the amplifying means.

Means are provided for amplifying the signals generated by the microphone M as a result of the detection of an intrusion. In this instance, the means comprises a multistage transistor amplifier utilizing NPN transistors. Specifically, transistor 0-1 is included in the first stage of the amplifier and has a biasing resistor R-l connected between its collector and its base, a load resistor R-2 connected between its collector and the positive line L-l, an' input resistor R-3 connected between its base and its negative line L-2, and a degeneration resistor R-4 connected between its emitter and the negative line L-Z. Under normal standby operating conditions, transistor 0-! will be biased to a nearly nonconducting state. However, when an intrusion is detected, the signal supplied by the microphone M through the blocking capacitor C-2 to the base of transistor 04 will cause the transistor to conduct and produce a signal at its collector, this signal being supplied to the next stage of the amplifier.

The second stage of the amplifier is similar, if not identical, to the first stage and includes transistor ()4 having a biasing resistor R-5 connected between its collector and its base, a load resistor R-6 connected between its collector and the positive line L-l, an input resistor R-7 connected between its base and the negative line L-Z, and a degeneration resistor R-8 connected between its emitter and the negative line L-2. A DC blocking capacitor (3-3 is connected between the collector of transistor Q-l and the base of transistor 0-2 and is used to couple the first stage of the amplifier to the second from the collector of transistor -2 and supplied to the third stage ofthe amplifier.

The third stage of the amplifier again is similar, if not identical, to the first two stages. Transistor 0-3 has a biasing resistor R-9 connected between its collector and its base, an input resistor R-ll connected between its base and the negative line l..-2, a load resistor R-10 connected between its collector and the positive line L-l, and a degeneration resistor R-l2 connected between its emitter and the negative line L-2. The third stage of the amplifier is also capacitively coupled to the second stage by means of a DC blocking capacitor C-4 which is connected between the collector of transistor 0-2 and the base of transistor 0-3.

The output of the amplifier is supplied to an alarm means which is responsive to generate an alarm signal which is to be transmitted along the telephone line L-l and L-2 back to a monitoring station. However, since random or external noise, such as from thunder or from the honking of the horn of a passing car, may activate the system, it is highly desirous to provide means within the system for preventing the alarm means from responding until a time interval has passed sufficient to insure that signals being received from the transducer are in response to an actual intrusion into the area being protected and not a false alarm.

Accordingly, the means for preventing an immediate 4 response of the alarm means includes an integration means and a switch means. The integration means provides a time delay which permits actuation of the alarm means only after a predetermined level of output from the transducer is reached, thus preventing actuation of the alarm from a false alarm source. The switch means is responsive to the integration means to apply the alarm means to the telephone line only after a predetermined level of output from the transducer is reached. In the preferred embodiment, the integration means includes a detector transistor 0-4 which is capacitively coupled to the output of the amplifier via a capacitor C-5 connected between the collector of transistor Q-3 and the base of transistor 0-4. An input resistor R-14 is connected between the base of transistor 04 and the negative to line L-2 with the emitter of transistor 0-4 being connected to the negative line L-Z through a field-effect current regulator diode D-3 and a voltage dividing and control network. Diode D-3 may be selected, for example, from the family of current limiter diodes having type numbers lN5283 through 1N53 l4 manufactured by Motorola Semiconductors. The voltage dividing and control network has two branches, one branch including series connected resistors R-17 and R-22 with the other branch including a diode D-l-connectedin shunt with a resistor R-l6, this circuit being serially connected to the negative line L-2 through an integrating capacitor 0-7.

The junction of resistors R-17 and R-22 is connected to the I I sufficient current passes through resistors R-17 and R 22, the

silicon controlled rectifier SCR-1 is "triggered" into its conducting state to connecting the alarm means across the telephone line.

In the operation of the preventing means, the output of the amplifier is supplied to the detecting transistor Q-4 causing the transistor to conduct. Thus, positive pulses appear at the emitter of the transistor, and current is supplied through diode D-3 and diode D-l to charge the integrating capacitor C-7. Diode D-3 is a current-limiting type diode which increases its forward resistance to prohibit current from exceeding a certain value and may be characterized as the electrical dual of the Zener diode. Diode D-3 thus prevents one extremelyloud sound from setting off the alarm, requiring, rather, that several sounds be present. Because of the low forward impedance of the diode D-l, resistor R-16 is effectively shunted. As the capacitor C-7 charges, the impedance looking into the diode D] rises diverting most of the current into the branch containing resistors R-17 and R-22. When the current level in this branch reaches a predetermined level, the silicon controlled rectifier SCR-l will be triggered" into i t s conducting state to apply the alarm means directly across telephone lines L-l and L-Z.

Note that resistor R-17 is necessary in order to overcome the effect of the forward voltage drop in the diode D-l.

' Without resistor R-l7 there would be little or no integration action since the amount of forward voltage developed across the diode would tend to immediately trigger the silicon controlled rectifier SCR-l before the capacitor C-7 was charged,

the result being that upon the detection of any sound by the transducer M, the alarm means would be applied to the telephone lines. Resistor R-l6 provides a controlled leak-off time for the charge on capacitor C-7, and provides controlled memory time for past sounds.

The alarm means comprises a unijunction oscillator circuit having a timing branch including a resistor R-20 connected in series with a capacitor C-6, the junction of these two elements being connected to the emitter electrode of a unijunction transistor 0-5. Base 2 of the unijunction transistor 0-5 is connected to the other side of resistor R-20 and to telephone line L-l while base 1 of the unijunction transistor Q5 is connected through a load resistor R-Zl to the other side of the capacitor C-6 and to telephone line L-2 through the silicon controlled rectifier SCR-l. A relatively low resistance R-l9 is connected in shunt across the unijunction oscillator circuit.

In the operation of the alarm means, the triggering of the silicon controlled rectifier SCR-immediately places the low resistance R-l9 directly across the telephone line and causes a relatively large flow of DC current through the line. This in turn initiates ringing of the telephone at the monitoring station which may be a police station or other suitable area. The unijunction oscillator circuit, the specific operation of which is well known in the art and which will not be described in any detail herein, is also activated by the telephone line voltage and will modulate the telephone line with a single continuous tone. Thus, an operator at the monitoring station answering the phone will hear the modulated signal and at once recog nize that an intrusion has occurred in the area being protected.

If desired, a telephone jack .l-l can also be connected across the unijunction oscillator circuit and utilized to provide an additional alarm device. For instance, an audible alarm mechanism similar to a buzzer could be installed. Or, an external carbon microphone, or a transistor amplifier with a magnetic microphone might be plugged into the jack to permit an audio monitoring of the area. The jack may also be used with an audible alarm to test the operation of the unit prior to its installation.

It generally will not be desirous to have the surveillance means continuously connected to a telephone line. Further, it

generally will be highly desirous to provide means for resetting the system, that is, where the capacitors C-1 and C-7 are completely discharged. Thus, means are provided for restoring the network to its original condition and for disconnecting the system from the line. Specifically, a double pole, double throw switch 8-] is utilized for both of these functions, one of the poles being used to control the connection of a discharge resistor R-18 to capacitor C-7 and the second pole being used to provide means for connecting another discharge resistor Rl3 across capacitor C-l. In the oft position of the switch 5- the resistor R-18 is connected directly across the capacitor C-7 to provide a means for dissipating any charge on the capacitor. Similarly, the resistor R-13 will be connected directly across the capacitor 0-1 to provide a means for dissipating any charge thereon. However, with the switch 5-1 in the on position, resistors R-13 and R48 will not be connected in the system and line voltage will be supplied to the system.

While we have shown and described only a particular embodiment ofthis invention, it will be obvious to those skilled in it without departing from its broader aspects. Therefore, it is the intention of the appended claims to cover all changes and modifications as fall within the true spirit and scope of this invention.

What we claim as new and novel and desire to secure by Letters Patent of the United States is:

1. An electronic surveillance means comprising:

a. Acoustical transducer means for converting sound energy into electrical signals;

b. Transistor means for amplifying said electrical signals;

c. Alarm means responsive to said amplified signals for indicating at a monitoring station an intrusion, said alarm means including;

1. a unijunction oscillator circuit,

2. a resistor connected in electrical shunt with said unijunction oscillator circuit, and

3. means for connecting said unijunction oscillator circuit and said resistor to a telephone line;

d. Means for preventing said alarm means from responding to said amplified signals until a predetermined time interval has passed sufficient to insure that said electrical signals from said transducer means is in response to an actual intrusion, said preventing means including;

1. solid state switching means for selectively connecting said alarm means to the telephone line,

the art that various changes and modifications may be made to I 2. integration means for controlling the operation of said solid state switching means, and 3. limiting means for limiting the current to said integration means thereby insuring that a sufficient number of sounds are present from an intrusion before said alarni means is activated. 2. An electronic surveiilance means as described in claim 1 wherein:

a. Said solid state switching means comprises a silicon controlled rectifier having a trigger electrode; and b. Said integration means comprises a capacitive network connected to the output of said amplifying means, a said capacitive network being coupled to said trigger electrode and controlling the conducting state of said silicon controlled rectifier, said silicon controlled rectifier operable to connect said unijunction oscillator circuit and said 7 resistor to a telephone line. 3. An electronic surveillance means as described in claim 2, further including:

a. Resistor means for dissipating any charge on said capacitive means to restore it to an uncharged condition, and b. Switch means operable to connect said resistor means directly across said capacitive means for dissipating any charge thereon.

Claims

1. An electronic surveillance means comprising: a. Acoustical transducer means for converting sound energy into electrical signals; b. Transistor means for amplifying said electrical signals; c. Alarm means responsive to said amplified signals for indicating at a monitoring station an intrusion, said alarm means including; 1. a unijunction oscillator circuit, 2. a resistor connected in electrical shunt with said unijunction oscillator circuit, and 3. means for connecting said unijunction oscillator circuit and said resistor to a telePhone line; d. Means for preventing said alarm means from responding to said amplified signals until a predetermined time interval has passed sufficient to insure that said electrical signals from said transducer means is in response to an actual intrusion, said preventing means including; 1. solid state switching means for selectively connecting said alarm means to the telephone line, 2. integration means for controlling the operation of said solid state switching means, and 3. limiting means for limiting the current to said integration means thereby insuring that a sufficient number of sounds are present from an intrusion before said alarm means is activated.

2. integration means for controlling the operation of said solid state switching means, and

2. An electronic surveillance means as described in claim 1 wherein: a. Said solid state switching means comprises a silicon controlled rectifier having a trigger electrode; and b. Said integration means comprises a capacitive network connected to the output of said amplifying means, a said capacitive network being coupled to said trigger electrode and controlling the conducting state of said silicon controlled rectifier, said silicon controlled rectifier operable to connect said unijunction oscillator circuit and said resistor to a telephone line.

3. An electronic surveillance means as described in claim 2, further including: a. Resistor means for dissipating any charge on said capacitive means to restore it to an uncharged condition, and b. Switch means operable to connect said resistor means directly across said capacitive means for dissipating any charge thereon.

3. limiting means for limiting the current to said integration means thereby insuring that a sufficient number of sounds are present from an intrusion before said alarm means is activated.

3. means for connecting said unijunction oscillator circuit and said resistor to a telePhone line; d. Means for preventing said alarm means from responding to said amplified signals until a predetermined time interval has passed sufficient to insure that said electrical signals from said transducer means is in response to an actual intrusion, said preventing means including;