Security devices

June 30, 1970

3,518,655

Β. B. SAUL

SECURITY DEVICES

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June 30, 1970

Β. B. SAUL

3,518,655

SECURITY DEVICES

Filed July 20, 1966

Sheets-Sheet 2

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United States Patent Office

3,518,655

Patented June 30, 1970

3,518,655 SECURITY DEVICES Benno B. Saul, 4742 St. James St. W., Montreal, Quebec, Canada Filed July 20,1966, Ser. No. 566,496 Int. Cl. G08b 13/08 U.S. Cl. 340—274 8 Claims

ABSTRACT OF THE DISCLOSURE

An alarm operated by the opening of a door or window contact simultaneously with unbalance in a bridge that can be balanced by use of the correct “key” in the form of a predetermined resistor. The combination can be changed by plugging in a different resistance in another arm of the bridge. The bridge circuit can also be used as part of an electrical lock without the alarm.

This invention relates to electrically operated security devices of the type that require a special “key” having a predetermined electrical value to operate them, and the invention has for its primary object an improvement in such devices that permits quick and convenient changing of the “combination,” that is to say a ready changing of the circuit in a manner that will immediately result in the need for a different key to operate the device, with former keys no longer being effective for this purpose.

One application of the invention is to the improvement of burglar alarm systems. Another application is to the enhancement of the security of any device that is normally closed by an electrically operated lock, for example, the access door of a typical vending machine. It is believed that the numerous possible uses to which the invention may be applied will become apparent from the examples that follow.

In its application to an alarm system, the invention may be directed towards a burglar or similar type of alarm system. However, as will appear from the description that follows, the system can also incorporate additional features that are typical of other types of alarm systems.

The object of this aspect of the invention is to provide an alarm system having improved facilities, and more particularly an especially convenient method by which the security of the system can be maintained in the event of loss of a “key” that affords access to the installed premises without triggering the alarm.

Various methods of carrying the inventoion into practice are illustrated diagrammatically and by way of example in the accompanying drawing. It is to be understood that the specific systems described are illustrated merely by way of example and not by way of limitation of the inventoion, the broad scope of which is defined in the appended claims.

In the drawings:

FIG. 1 shows a schematic circuit diagram of an alarm system, with certain parts also shown in physical form;

FIG. 2 is a circuit diagram of an alternative alarm system; and

FIG. 3 demonstrates the application of the invention to the control of an electrically operated lock.

The circuit of FIG. 1 includes a source of power represented by lines 10 and 11, which may be connected to a battery or any other convenient source of power, either alternating or direct current as required. In practice, the various parts of the system may operate at different voltages and have individual power supplies, D.C. for the loop circuit and A.C. for the bridge. However, for the purposes of schematic illustration of the principles of the invention, a single power supply has been shown for simplicity.

The system includes means sensitive to an alarm condition, in the form of a conventional series circuit of door and window contacts 12, these being connected across the power supply and in series with a relay 13. When all the contacts 12 are closed, the relay 13 is energized and its contacts 14 are held open. When any one of the contacts 12 is opened, the relay 13 is released to close its contacts 14. This arrangement is entirely conventional.

When the contacts 14 are closed they complete a first circuit 17 to an AND gate 18, the output of which triggers an alarm 19 which is connected across the power supply through a main ON-OFF switch 20. The exact nature of the alarm 19 may vary widely. It may include both visual and audible alarm devices, as well as such additional features as direct communication with a central station or a police switchboard. The alarm 19 will be such that it will continue to operate once triggered, whether or not a signal continues to be received by it from the gate 18. Such features of alarm devices are known and the present invention is not concerned with these details. In addition, the alarm 19 may include another triggering circuit (not shown) for actuation by sensors designed for detecting smoke or fire.

A second circuit 21 leads to the AND gate 18, and the latter is only actuated to trigger the alrm 19 when inputs are received by the gate simultaneously from both input circuits 17 and 21. The circuit 21 is essentially the output from a balanced detector circuit which is shown generally at 22 and which, in the specific example, consists of a bridge, two arms of which comprise resistors 23 and 24 connected through a series resistor 25 across the power supply. The third arm of the bridge is constituted by a resistor 26 mounted in a plug 27 which can be inserted into a socket 28 to connect the resistor 26 in circuit. The fourth arm of the bridge comprises a resistor 29 that is mounted in a plug or “key” 30 which fits into a socket 31 to connect this resistor in the bridge circuit through contacts 32 and 34 that are insulated from each other by material 33. The resistors 26 and 29 form a matched pair of bridge elements that serve to bring the bridge to a balanced condition, when they are both in circuit. When the; bridge is balanced there is no output in line 21. Also in the same arm of the bridge as resistor 29 there is located a fuse 34.

The system also inludes a series resistor 35 in the circuit 21 connecting the detector circuit 22 to the gate 18 and a Zener diode 36 is connected across the circuit 21 and ground.

The system may typically be used in the following manner by a householder, in whose house the system is installed. Assume that the householder is outside his house and that all the door and window contacts 12 are closed. The relay 13 will thus be energized to open contacts 14 so that the gate 18 receives no energization through circuit 17. The householder is then free to remove the key 30 from its socket 31 and leave the house unattended. The detector circuit 22 is now unbalanced, so that a signal appears on line 21 at the input to the gate 18. Thus, whenever any one of the door or window contacts 12 is opened by an intruder to release the relay 13 and close the contacts 14, the gate 18 will be operated to trigger the alarm 19.

When the householder returns, assuming that the alarm has not been triggered in his absence by an intruder, he inserts his key 30 into its socket 31 to balance the detector circuit 22. He is then free to open any of the doors and windows, because the gate 18 is no longer receiving a signal on the line 21 and an input from the line 17 alone is insufficient to operate the gate. Once inside the house, the owner will normally switch off the system at the main switch 20, although, if it is desired to leave the alarm in operation while the owner is inside the house,

3,518,655 for example during the night, this is possible by simply removing the key 30, closing all the contacts 12 and turning on the alarm at the switch 20. Indeed, when the owner is inside the house, he will not normally leave the key 30 in place, since the socket 31 will be located at a convenient outside position, e.g. beside the front door on the outside of the house.

To enable a housewife to answer a call at the front door, while having the alarm system operative, a pushbutton switch 37 is provided in parallel with the contacts 12 of the front door. She sets the alarm by the switch 20 (assuming the key 30 not to be in place) and holds the pushbutton 37 depressed as she opens the front door. The switch 37 will be located at a convenient position somewhere on or near the rear surface of the front door. The relay 13 will remain unreleased while the front door is open, provided the switch 37 remains depressed. Should the caller attempt to force his way into the house, release of the switch 37 will set off the alarm.

A further feature of the system is the provision of neon lamps 38 connected across each of the door and window contacts 12. These lamps are particularly useful in locating a pair of open contacts when the alarm is being set. When setting the alarm it is sometimes found that the alarm is triggered, although it was thought that all the contacts were closed. One of the pairs of contacts 12 must be improperly closed, but without the lamps 38 it can be quite a time consuming job to And out which are the faulty contacts. The lamp 38 corresponding to the improperly closed pair of contacts will glow, because substantially the full supply voltage will be across it, and this will provide an immediate indication of which door or window requires to be more firmly secured. The lamps 38 may be arranged on a control panel with other parts of the alarm and the main switch 20, or they may be individually mounted adjacent the respective doors and windows themselves.

In the event that a key 30 is lost, with the possibility that it might have fallen into the hands of an unauthorized person, security can be immediately restored by merely replacing the plug 27 with a different plug 27 containing a resistor 26 of a different resistance value. A new key 30 to match must of course also be provided. In other words, the key 30 and the plug 27 represent a matched pair Of elements, for which any other similarly matched pairs of elements may be substituted. In this connection, the term “matched” is not intended to suggest that the resistors are equal in resistance value, but rather that the ratio of their resistance values is predetermined. Such ratio will, of course, be equal to the ratio of the resistance values of the resistors 23 and 24 in the first two arms of the bridge. Thus, not only is a very large number of “combinations” possible for each installation, but the particular combinations of plug and key that provide balance in one installation will not normally do so in another. The ratio of the values of resistors 23 and 24 can be varied from installation to installation, so that each installation is virtually unique in this respect.

The fuse 34 is provided to prevent the system being rendered inoperative by an unauthorized person who might attempt to introduce a destructively high voltage into the system through the socket 31. If a high voltage were applied at the socket 31, the fuse 34 would rupture and prevent damage to the gate 18 or alarm 19. Once the fuse 34 has been ruptured, the circuit 22 will remain permanently out of balance and hence the alarm will always be operative, until the fuse 34 has been replaced. If desired, the fuse 34 can also be formed as a separate plug-in element, and indeed may be incorporated physically in the same plug 27 as the resistor 26, if this is convenient. The Zener diode 36 similarly provides a shunt path for protection against excess currents or voltages.

In the event that an alternating supply to the bridge circuit is employed, the electrically matched elements may be capacitors and/or inductors, instead of the resistors 26 and 29, although normally resistors would be used, because of their simplicity. By the same token, the circuit 22 need not necessarily be a bridge. Any other known circuit may be used as the detector circuit, that contains a pair of elements that are matched to each other so as to “balance” the circuit, i.e., yield a substantially zero output, and in which such elements may be replaced with equal effect by other similar but different pairs of matched elements.

FIG, 2 shows an alternative circuit that is especially designed for alternating current operation, to avoid the need for batteries for supplying the main operating power, and which circuit has additional fail safe characteristics, as will be described.

In FIG. 2, the alternating voltage input is applied across terminals 40, 41. The detector circuit is again in the form of a bridge, comprising resistors 42, 43, 44 and 45. Resistors 42 and 43 are fixed (corresponding to resistors 23, 24); resistor 44 will be mounted in a plug (as resistor 26) and resistor 45 represents the “key” (i.e., corresponds to the resistor 29). For simplicity the resistors 44 and 45 have not been shown in their physical forms, since this would merely be a repetition of FIG. 1, but, as before, they form a matched pair, so that the combination can readily be changed by fitting a new resistor 44 and providing a corresponding new key 45.

Also connected to input terminal 40 is a series circuit of a diode 46 and resistors 47, 48 and 49 extending to a minus 12 volt potential. A tap 50 on the resistor 48 provides a controllable positive bias voltage which is smoothed by the decoupling condenser 51 and fed through a resistor 52 to the base of an NPN transistor 53 thus normally keeping the same forward biased and switched on, the collector of the transistor being connected through resistor 54 to a positive 12 volt potential. The output of the bridge circuit appears across terminals 55 and 56, the former of which is grounded and connected to the emitter of the transistor 53, and the latter of which is connected to the other side of the condenser 51.

With, the bridge balanced, i.e., the correct “key” resistor 45 in place, the transistor 53 will remain conducting. When the bridge becomes unbalanced the terminal 56 will carry an alternating voltage, the negative portion of which will reduce the positive bias on the transistor base to shut the same down. It will be noted that the collector circuit of the transistor includes some door and window contacts 60. Thus, if any one of these is now opened, i.e., with the transistor 53 shut down, the terminal 57 goes more. positive and this positive potential triggers a gating diode 58 which in turn energises a relay in an alarm 59.

It will be appreciated that the operation of the circuit of FIG. 2 will be generally similar to that of FIG. 1, in that in FIG. 2 the alarm will be energised by the simultaneous opening of a pair of contacts 60 and unbalance in the detecting circuit.

As an alternative, the collector of the transistor 53 may be connected to the terminal 57 through some of the contacts 60. For example, in FIG. 2, if the transistor collector were connected to the point between the two contacts 60 illustrated, as shown in broken lines, and the contact 60 to the left of such connection were assumed to represent the front door while the other contact 60 shown represents all the other door and window contacts, the situation would exist that the alarm would be triggered either (a) when both the bridge is unbalanced and the front door is open (thus permitting the front door to be opened without triggering the alarm, when the key 45 is in place); or (b) when any one of the other door and window contacts

3,518, is open (regardless of balance or unbalance in the bridge).

When operating in this latter manner the other door and window contacts will always be effective to trigger the alarm, whenever they are opened, and can only be 5 rendered inopertaive by switching off the entire device at the main switch 61.

The circuit is fail safe, because any failure in the circuit supplying the positive bias voltage to the transistor 53 will have the effect of cutting off or reducing such bias 10 voltage sufficiently to shut down the transistor and trigger the alarm. If any person attempts to harm the circuit by applying a high external voltage across the socket where the resistor 45 is mounted, this voltage, if negative, will be shorted out by diode 62, and, if positive or con- 15 taining a positive portion (i.e. an alternating voltage) will trigger the diode 58 and hence the alarm 59 through resistors 63 and 64. Zener diode 65 is provided for protection of the transistor 53 from an externally applied excessive voltage. A fuse 66 is also provided for protection 20 against excessive currents.

FIG. 3 shows another way in which the invention can be carried into practice to protect a security device, in this case an electrically operated lock 70, which could, as above mentioned be the lock on a vending machine. 25 To open the lock 70 its solenoid coil 71 must be energised, and this may, for example, be achieved from power supply terminals 68, 69 by a pair of contacts 72 operated by a conventional mechanical key 79, in series with a pair of normally closed contacts 73 operated by a relay ³⁰74 which is only deenergised when a detector circuit 75 is balanced. The circuit 75 comprises a pair of fixed resistors 76 and 77, a plug-in resistor 78 (corresponding in function to the resistor 26), and a “key” resistor 80, which corresponds in function to the resistor 29. It is believed ³⁵that the operation of this circuit will be clearly evident, both keys, i.e., the mechanical and the electrical being necessary to operate the lock. The important practical advantage of this arrangement is the ease with which the “combination” can be changed, should the mechanical key be lost or stolen. It is then unnecessary to change the mechanical parts of construction which is a relatively complicated undertaking. It is merely necessary to substitute a new resistor 78 of different resistance value, and in practice this can be done merely by substituting a fresh plug containing the new resistor. This can be done in a matter of seconds by an unskilled operator.