US3522488A - Antidetecting network for pushbutton combination lock - Google Patents

Description

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7 ANTIDETECTING NETWORK FOR PUSHBUTTON COMBINATION LOCK Filed Nov. 1, 1967 g ue INVENTOR. fozoarv )f filler/27a ATTUAIVIVS United States Patent 3,522,488 ANTIDETECTING NETWORK FOR PUSHBUTTON COMBINATION LOCK Edward M. Tellerman, East Rockaway, N.Y., assignor to Continental Instruments C0rp., Lynbrook, N.Y., a corporation of New York Filed Nov. 1, 1967, Ser. No. 679,872 Int. Cl. E05b 47/00 US. Cl. 317134 Claims ABSTRACT OF THE DISCLOSURE An antidetecting network for a combination lock of the type having a plurality of pushbuttons wherein the actuation of a preselected number, less than all, of said pushbuttons in predetermined sequence is operable to release said lock. There is provided switch means in the path of the energizing current for the locking release mechanism which switch means prevents the flow of such energizing current unless all of the pushbuttons have been pushed. The switch means is under the control of a relay coil which, so long is energized, causes the switch means to prevent current flow to the release mechanism. The relay coil becomes unenergized only after all pushbuttons have been actuated to prevent the detection of the particular pushbuttons involved in the combination.

BACKGROUND OF THE INVENTION In recent years, coded electrically operated actuating devices have become more and more popular for use in connection with locking devices, gradually replacing the conventional mechanical type combination lock which had been in predominant use. Such coded actuated devices are often of the type wherein release or unlocking is accomplished by the actuation of a specific number of pushbuttons in a preselected sequence. Thus, of a plurality of pushbuttons presented, it is the actuation of a specified number of these, usually less than all, in preselected sequence which etfectuates release of the locking mechanism.

The advantages of such arrangement over the predecessor mechanical arrangement are as obvious as they are numerous.

An example of an electrical pushbutton actuated locking device of the type involved herein is fully disclosed in US. Pat. No. 3,242,388 dated Mar. 22, 1966 and assigned to the assignee hereof. This patent discloses in great detail the circuitry associated with an electronic locking device wherein the actuation of a number of pushbuttons in preselected sequence, in accordance with a preselected particular code, is efiective to operate the locking release mechanism. The circuitry as disclosed in said patent includes numerous safeguards to prevent detection of the particular combination which has been set. Thus, for example, such circuitry includes means for disabling the operation of the device for a predetermined interval upon improper operation thereof. In accordance with the locking device as set forth in Pat. No. 3,242,388, the correct actuation of the pushbuttons in the sequence as ordained by the preselected code results in the release of the locking mechanism for an adjustable finite period of time, long enough to permit unlocking of the door, after which the release mechanism is automatically rendered inoperative.

While the electronic locking device of the prior art, specifically as exemplified in U.S. Pat. No. 3,242,388, goes a long way in providing a system whose operating code cannot easily be detected, it does not go the entire distance. For example, one of the most effective ways of compromising the pushbutton operated electronic locking device is by a method commonly known as dusting. In accordance 3,522,488 Patented Aug. 4, 1970 with one type of dusting, the pushbuttons are dusted with a chemical before an authorized person operates the pushbutton panel to gain access to the unauthorized area. After such authorized person has gained access, the pushbutton panel is examined, and by simple chemical analysis, the particular buttons which have been pushed can easily be identified, reducing the number of possible combinations to a number small enough to enable detection of the correct combination within a relatively short period of time. Thus, with a ten button pushbutton panel and a code utilizing four buttons, providing upwards of 5000 possible combinations, the detection of the particular four pushbuttons reduces the number of possible combinations to 24. If only three buttons form part of the code, providing for 720 possible combinations, the detection of the three particular pushbuttons involved reduces the number of possible combinations to 6. Thus it is seen that the dusting method which results in the identification of the individual push buttons involved in the particular code seriously compromises the locking device as it enables detection of the particular combination within a relatively short period of time.

SUMMARY OF THE INVENTION In accordance with the present invention, the aforementioned disadvantages are obviated. More specifically, in accordance with the invention, in addition to pushing the requisite number of pushbuttons in the predetermined sequence, as preordained by the code, the operator is required to push all of the buttons before the unlocking mechanism is released.

Thus in accordance with the invention, the operator is first required to push the preselected buttons in the ordained sequence resulting in the partial completion of the energizing circuit for the unlocking mechanism, such partial completion persisting for a predetermined finite period of time. During such finite period of time, the operator is required to push all of the buttons on the pushbutton panels to complete the circuitry for releasing the unlocking mechanism. Accordingly, the present invention imposes on the operator the further obligation to push all of the buttons before the door can be opened. This requirement obviously eliminates the possibility of detecting, as by dusting, the particular pushbuttons initially required to be pushed to operate the release mechanism.

In accordance with an alternate form of the invention, complete release of the unlocking device for the door is accomplished first by pushing the requisite pushbuttons in accordance with the preselected code in the proper sequence, followed by the pushing only of those buttons not involved in the original coded combination.

BRIEF DESCRIPTION OF THE DRAWING The drawing represents a schematic circuit diagram of the anti-detecting network in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, PBI, PBZ, and PB3 represent three of the pushbuttons provided in an electronic unlocking device having as many additional pushbuttons (not shown) as may be deemed desirable. In accordance with such electronic unlocking device, the actuation of a preselected number of such pushbuttons in a preselected sequence is effective to operate the lock release mechanism, such unlocking device being fully described in previously mentioned Pat. No. 3,242,388. Effectively, the actuation of the pushbuttons as ordained by the code, is operative, by means of the circuitry described in said Pat. No. 3,242,388 to energize an output relay (not shown) which in turn controls switch SW2, causing the latter to move from its engagement with contact 12 (as shown in the drawing) into engagement with contact 14. Such actuation of switch SW2 forms a continuous path through electric door strike operating relay 15 which permits opening of the door, provided however that switch SW1 is in engagement with contact 17. Under such conditions, current flow is from positive terminal 16 through switch SW2, contact terminal 14, switch SW1, contact terminal 17, relay 15 and negative terminal 19. In the drawing, switches SW1 and SW2 are shown in position corresponding to the unenergized condition of their respective operating relays.

Each of said pushbuttons PBl, PB2, PB3, etc. is a double pole single throw switch, one pole of which is used in connection with the unlocking mechanism as aforedescribed, and the other pole of which is shown in the drawing and is used for the objects of the present invention. Thus, PBl, when actuated, closes contacts 10 thereof, PB2 when actuated closes contacts 2020 thereof, and PB3 when actuated closes contacts 30-30 thereof. While only three pushbuttons are shown, it will be understood that there are provided as many pushbuttons with circuitry identical to that shown as may be desired for a particular unlocking device.

Each pushbutton is associated with a condenser, as for example, condenser C1 with pushbutton PBl, condenser C2 with pushbutton PB2, and condenser C3 with pushbutton PB3. In the position of switch SW2 shown in the drawing, which corresponds to the unenergized condition of the output relay of the electronic unlocking device, there is a continuous path from positive terminal 16, switch SW2, terminal 12, resistor R18, oneway diode CR1, condenser C1 and negative terminal 22 defining a charging circuit for condenser C1. Similarly, when SW2 is in the position shown in the drawing, there is a continuous path from positive terminal 16, switch SW2, terminal 12, resistor R18, one-way diode CR2, condenser C2, terminal 24, terminal 26, and negative terminal 22, defining a charging circuit for condenser C2. In the same manner, a continuous path exists from positive terminal 16, through switch SW2, terminal 12, resistor R18, one-way diode CR3, condenser C3, terminal 24, terminal 26, and negative terminal 22, defining a charging circuit for condenser C3. Thus, it is seen that all of the condensers C1, C2., C3, etc. are charged when SW2 engages terminal 12, corresponding to the inoperative condition of the unlocking mechanism.

Q is a conventional transistor amplifier which becomes conductive when there is current flow through its emitter. As shown in the drawing, transistor Q is in a conductive state when switch SW2 is in engagement with contact 12, corresponding to the inoperative condition of the unlocking mechanism. In such condition, there is a continuous path from positive terminal 16, switch SW2, resistor R18, diode CR1, one-way diode CR4, (also through parallel paths CR2-CR5 and CR3-CR6), resistor R32 and negative terminal 34. Such current flow through the emitter of transistor Q renders the latter conductive to provide a current path from positive terminal 36, relay 38, transistor Q and negative terminal 34, causing energization of relay 38. Relay 38, when energized, is operative to move switch SW1 which is under its control away from engagement with terminal 17. Thus, the energization of relay 38 prevents the electric door strike relay from being energized. Conversely, only when relay 38 is unenergized, corresponding to the non-conductive state of transistor Q, is switch SW1 in engagement with contact 17. Accordingly, in order for the electric door strike relay to be energized, and for the unlocking of the door to be possible, transistor Q must be non-conductive at the same time that switch SW2 is in engagement with contact 14.

It has been demonstrated above that when switch SW2 is in engagement with contact 12, transistor Q is conductive whereby switch SW1 is open, preventing the energization of relay 15. When the pushbutton combination is activated in accordance with the preselected code, SW2 will engage contact 14, without however interrupting current flow to the emitter of transistor Q, as such current flow is maintained as a result of the discharge of condensers C1, C2, C3, etc. More specifically, the charge on condenser C1 causes current flow from condenser C1 through terminal 28, diode CR4, resistor 32, the emitter of transistor Q, negative terminal 34, negative terminal 26, and back to condenser C1. Such current flow maintains conductivity in Q to thereby maintaln relay 38 energized and switch SW1 open. In this connection, it will be noted that the capacitance of C1 and resistance of R2 is such as to provide a total discharge time which exceeds the finite period of time during which SW2 remains in engagement with contact 14, following a correct actuation of the pushbuttons. Accordingly, the discharge of C1, C2, C3, or of any of the other condensers prevents energization of the electric door strike relay. The only way to prevent condenser C1 from discharging and maintaining triggering current flow for Q is to discharge said condenser instantaneously by actuation of pushbutton PBl. Such actuation of PBl W111 provide for the instantaneous discharge of condenser C1 through resistor R36. In order to completely cut 01f triggering current flow, all other condensers must similarly be discharged by actuation of the associated pushbutton. Thus, in addition to PBl, pushbuttons PB2, PB3 and all others in the system will have to be pushed to discharge their associated condensers and cut off all trigger current flow. When all such trigger current flow has been interrupted, during the time interval that SW2 1s 1n engagement with contact 14, Q will become nonconductive to de-energize relay 38 and place switch SW1 1n engagement with contact 17 in order to complete the circuit for energization of electric door strike relay 15. It will be noted that one-way diode CR4 prevents the discharge of all condensers except C1, upon actuation of pushbutton PB1. Similarly, one-way diodes CR5 and CR6 perform a corresponding function upon actuation of pushbuttons PB2 and PB3, respectively.

From the above, it is clear that, though the preselected pushbuttons have been actuated, in accordance with the predetermined sequence, it is still necessary thereafter to actuate all of the pushbuttons before the unlocking mechanism can effectively permit opening of the door. The requirement to have all pushbuttons actuated thus eliminates the possibility of detecting the particular buttons which are part of the code combination.

In the embodiment described above, it is clear that all of the pushbuttons on the panel must be pushed before the door can be opened and this includes the pushing of those buttons which may already have been pushed in accordance with the code combination. If the repeated pushing of the pushbuttons involved in the combination is desired to be eliminated, such can be accomplished in any one a plurality of ways. A simple way would be to provide a toggle switch immediately in series with each condenser, with toggle switch would remain closed for all pushbuttons except only those involved in the particular preselected combination. Thus, when the combination for the unlocking mechanism is initially set, the toggle switches associated with the pushbuttons involved in the combination would be opened, preventing the condensers associated with the preselected pushbuttons from discharging into triggering circuit for transistor Q. For example, the toggle switch for pushbutton PBI could be located between C1 and terminal 28 or anywhere else along the discharge path of said condenser through transistor Q. In this manner, the pushbuttons involved in the combination need only be pushed once, for the purpose of energizing the output relay which controls switch SW2.

While I have herein shown and described the preferred embodiments of my invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that in the illustrated embodiments certain changes in the details of construction and in the form and arrangement of parts may be made without departing from the underlying idea or principles of this invention within the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In a combination lock mechanism having a plurality of pushbuttons wherein the actuation of particular preselected pushbuttons less than all of said pushbuttons in predetermined sequence is operable to actuate a switch in an electrical path forming part of an electrically operated lock mechanism, the improvement comprising open second switch means interposed in said electrical path and preventing current flow therethrough, and electrical control means closing said second switch means in response to the actuation of all of said pushbuttons subsequent to the actuation of said particular ones, whereby failure to subsequently actuate all of said pushbuttons prevents release of said lock mechanism.

2. The improvement in accordance with claim 1 wherein said electrical control means comprises a relay coil which, when unenergized, causes said second switch means to close.

3. The improvement in accordance with claim 2 wherein there is provided a transistor amplifier having its collector connected to said relay coil whereby the latter can be energized only when said transistor amplifier is in a conducting state.

4. The improvement in accordance with claim 3 .wherein each pushbutton is associated with a condenser connected in a charging circuit therefor which is energized before actuation of said preselected buttons in said predetermined sequence.

5. The improvement in accordance with claim 4 wherein each condenser is connected to the emitter circuit of said transistor whereby upon actuation of said preselected buttons in said predetermined sequence each condenser discharges through said emitter circuit to provide triggering current for said transistor.

6. The improvement in accordance with claim 5 wherein each of said pushbuttons is connected to its associated condenser so as to instantaneously discharge the latter upon actuation thereof, thereby preventing the associated condenser from discharging through the triggering circuit of said transistor.

7. In a combination lock mechanism having a plurality of pushbuttons wherein the actuation of particular preselected pushbuttons less than all of said pushbuttons in predetermined sequence is operable to actuate a switch in an electrical path forming part of an electrically operated lock mechanism, the improvement comprising open second switch means interposed in said electrical path and preventing current flow therethrough, and electrical control means closing said second switch means in response to the actuation of the pushbuttons other than said particular ones subsequent to the actuation of said particular ones, whereby failure to sub sequently actuate the pushbuttons other than said particular ones prevents release of said lock mechanism.

8. The improvement in accordance with claim 7 wherein said electrical control means comprises a relay coil which, when unenergized, causes said second switch means to close.

9. The improvement in accordance with claim 8 wherein there is provided a transistor amplifier having its collector connected to said relay coil whereby the latter can be energized only when said transistor amplifier is in a conducting state.

10. The improvement in accordance with claim 9 wherein each pushbutton is associated with a condenser connected in a charging circuit therefor which is energized before actuation of said preselected buttons in said predetermined sequence.

References Cited UNITED STATES PATENTS 3,242,388 3/1966 Teller-man 317134 3,383,887 5/1968 Harris et a1. -313 X 3,441,808 4/1969 Crane 317134 J. D. MILLER, Primary Examiner W. J. SMITH, Assistant Examiner US. 01. X.R.

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