U.S. patent number 3,673,467 [Application Number 05/084,679] was granted by the patent office on 1972-06-27 for resistively-coded security system.
This patent grant is currently assigned to Eaton Corporation. Invention is credited to William Eisenreich.
United States Patent |
3,673,467 |
Eisenreich |
June 27, 1972 |
RESISTIVELY-CODED SECURITY SYSTEM
Abstract
An electronic key-actuated security system including keys each
constituted by a plurality of electrically resistive elements.
Key-receiving means includes conductors which provide connections
with resistive elements of a key received. The system includes a
plurality of bridges each associated with one of the resistive
elements of a key received. Each of said bridges has first, second
and third impedance arms, a respective one of the key resistive
elements being connected as a fourth impedance arm of each said
bridge. The first and second arms define a first preset impedance
ration, and the third and fourth arms define a second impedance
ration, the bridge being electrically balanced when these ratios
are equal. Logic gate means is interconnected with each of the
bridges and supplies an output signal when all of the bridges are
balanced. Electrically actuatable means, e.g., a latch, is
responsive to this output signal for indicating thereby the
receiving of a key having resistive elements causing balancing of
all the bridges. A key for use with the system includes a
nonconductive portion adapted to be inserted in the key-receiving
means. Pairs of contacts are bilaterally symmetrical with respect
to an axis of symmetry extending in the direction of insertion of
the key with the result that the key is adapted for bilateral
insertion.
Inventors: |
Eisenreich; William (White
Plains, NY) |
Assignee: |
Eaton Corporation (Cleveland,
OH)
|
Family
ID: |
22186533 |
Appl.
No.: |
05/084,679 |
Filed: |
October 28, 1970 |
Current U.S.
Class: |
361/172; 361/187;
338/260; 361/205 |
Current CPC
Class: |
G07C
9/00714 (20130101); G07C 9/20 (20200101) |
Current International
Class: |
G07C
9/00 (20060101); E05b 049/00 (); H01c 001/02 () |
Field of
Search: |
;317/134
;70/277,278 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hix; L. T.
Claims
What is claimed is:
1. Apparatus for use in an electronic key-actuated security system
including keys each constituted by a plurality of electrically
resistive elements, said apparatus comprising:
key-receiving means including conductors for providing connections
with resistive elements of a key received;
a plurality of bridges, each associated with a resistive element of
a key received, each of said bridges including first, second and
third impedance arms, said key-receiving means being adapted to
connect a respective one of said resistive elements as a fourth
impedance arm of each of said bridges, said first and second
impedance arms defining a first preset impedance ratio, said third
and fourth impedance arms defining a second impedance ratio, each
of said bridges having first and second output terminals having a
potential thereon with the potential developed at said first
terminal being indicative of the first preset impedance ratio and
the potential developed at said second terminal being indicative of
said second impedance ratio, each of said bridges being adapted to
be electrically balanced to apply equal potentials to said first
and second output terminals when said impedance ratios are equal; a
plurality of differential amplifiers, each associated with one of
said bridge circuits, and each having an output which is a function
of said impedance ratios;
logic gate means interconnected with said differential amplifiers
and responsive to an output signal of said differential amplifier
which is indicative of predetermined ratios being developed between
the potentials on said first and second output terminals of each of
said bridges for supplying an output signal only when the
potentials developed on said first and second output terminals of
each of said bridges form said predetermined ratios; and
electrically actuatable means responsive to said output signal for
indicating thereby the receiving of a key having resistive elements
of respective resistance values causing said predetermined ratios
to be developed on all of said bridges.
2. Apparatus as set forth in claim 1 wherein said logic gate means
comprises a plurality of AND gates each associated with one of said
bridges and each connected for providing an intermediate signal in
response to balancing of the associated bridge, and a further AND
gate interconnected with each of the first-said AND gates and
adapted to supply the first-said output signal in response to
intermediate signals from each of the first-said AND gates.
3. Apparatus for use in an electronic key-actuated security system
including keys each constituted by a plurality of electrically
resistive elements, said apparatus comprising:
key-receiving means including conductors for providing connections
with resistive elements of a key received;
a plurality of bridge circuits, each associated with a resistive
element of a key received, each of said bridge circuits including
first, second and third impedance arms, said key-receiving means
being adapted to connect a respective one of said resistive
elements as a fourth impedance arm of each of said bridge circuits,
said first and second impedance arms defining a first preset
impedance ratio, said third and fourth impedance arms defining a
second impedance ratio, each of said bridge circuits being adapted
to be electrically balanced when said ratios are equal;
a plurality of differential amplifiers, each associated with one of
said bridge circuits, and each having an output which is a function
of said ratios;
logic gate means responsive to the outputs of said differential
amplifiers for supplying an output signal when said ratios are
equal for each of said bridge circuits;
each of said differential amplifiers including a pair of inputs
connected across a respective one of said bridge circuits and a
pair of differential outputs connected to a respective pair of
inputs of said logic gate means; and
electrically actuatable means responsive to said output signal for
indicating thereby the receiving of a key having resistive elements
of respective resistance values causing balancing of all of said
bridge circuits.
4. Apparatus for use in an electronic key-actuated security system
including keys each constituted by a plurality of electrically
resistive elements, said apparatus comprising:
key-receiving means including conductors for providing connections
with resistive elements of a key received;
a plurality of bridge circuits, each associated with a resistive
element of a key received, each of said bridge circuits including
first, second and third impedance arms, said key-receiving means
being adapted to connect a respective one of said resistive
elements as a fourth impedance arm of each of said bridge circuits,
said first and second impedance arms defining a first preset
impedance ratio, said third and fourth impedance arms defining a
second impedance ratio, each of said bridge circuits being adapted
to be electrically balanced when said ratios are equal;
a plurality of differential input voltage comparators, each
associated with one of said bridge circuits, and each having an
output which is a function of said ratios;
logic gate means responsive to the outputs of said voltage
comparators for supplying an output signal when said ratios are
equal for each of said bridge circuits; electrically actuatable
means responsive to said output signal for indicating thereby the
receiving of a key having resistive elements of respective
resistance values causing balancing of all of said bridge circuits;
and
said logic gate means comprising a plurality of AND gates each
associated with one of said bridge circuits and each having a pair
of inputs connected for being supplied with input potentials of
preselected equal level in response to balancing of the associated
bridge circuit to cause the AND gate to provide a potential at the
output thereof, and a further AND gate having input terminals
interconnected with the outputs of each of the first-said AND
gates, the output of said further AND gates supplying said output
signal when each of the first-said AND gates provides a respective
output potential.
5. Apparatus as set forth in claim 4 further comprising a plurality
of voltage comparators each having a pair of differential inputs
connected across a respective one of said bridge circuits and a
pair of differential outputs connected to a respective pair of
inputs of one of the first-said AND gates.
6. Apparatus as set forth in claim 5 wherein said electrically
actuatable means comprises an electric latch and a triggerable
semiconductor switching device interconnected for energizing said
latch when triggered, said output signal causing triggering of said
switching device.
7. Apparatus as set forth in claim 6 including an alarm signalling
device, time delay means operative in response to receiving of a
key for energizing said signalling device after a predetermined
time delay period following the receiving of the key, and means
operative in response to said output signal for preventing
energization of said signalling device.
8. Apparatus as set forth in claim 7 including a logic OR gate
having a plurality of inputs each interconnected with one of said
voltage comparators, and wherein said means for preventing
energization comprises a still further AND gate having one input
terminal interconnected with the output terminal of said OR gate,
another input terminal adapted to be supplied with a potential in
the absence of said output signal, and an output terminal connected
for causing energization of said time delay means, said output
signal thereby preventing energization of said time delay means so
as to prevent energization of said signalling means.
9. Apparatus for use in a key-actuated security system including
keys each constituted by a plurality of electrically resistive
elements, said apparatus comprising:
key-receiving means including conductors for providing connections
with resistive elements of a key received;
a plurality of voltage dividers, each including a preset impedance
and each adapted to have a resistive element of a received key
interconnected with said preset impedance by said key-receiving
means and with a voltage source to provide a first potential whose
level is a function of said impedance and the resistance value of
the interconnected respective element;
means for supplying a reference potential;
a plurality of voltage comparators, each associated with one of
said voltage dividers and each having a pair of differential input
terminals and a pair of differential output terminals, the
potentials at the output terminals of each comparator being of
predetermined equal levels when the levels of potentials applied to
the input terminals thereof have a predetermined relationship;
circuit means for applying said first potential provided by each
voltage divider to one of said input terminals of the respective
comparator and applying said reference potential to the other of
said comparator input terminals;
logic gate means, including an AND gate, connected to each of said
output terminals and providing an output signal when the potentials
at each pair of said comparator output terminals are each of said
predetermined equal levels; and
electrically actuatable means responsive to the output signal from
said logic gate means for indicating thereby the receiving of a key
having resistive elements of resistance values producing said
predetermined relationship.
10. A key-actuated security system comprising:
a key including a plurality of electrically resistive elements,
each of a preselected resistance value;
means for receiving said key including conductors for providing
connections with resistive elements of said key;
a plurality of circuit means each associated with a resistive
element of said key, each of the circuit means including a preset
impedance and each adapted to have the associated resistive element
of said key interconnected with said preset impedance by the
key-receiving means, each of the circuit means providing a first
potential whose level is a function of said preset impedance and
the resistance value of the interconnected resistive element;
means for supplying a reference potential;
a plurality of voltage comparators each associated with one of said
circuit means and each responsive to said first and reference
potentials, each of said comparators including output terminals
providing potentials which are of predetermined equal level when
said first and reference potentials have a predetermined
relationship;
logic gate means interconnected with the output terminals of each
of said comparing means and providing an output signal when the
output potentials at each pair of output terminals are each of said
predetermined equal level; and
electrically actuatable means responsive to said output signal for
indicating thereby that said key when received has resistive
elements of preselected resistance values producing said
predetermined relationship.
Description
BACKGROUND OF THE INVENTION
The present invention relates to electronic lock systems or
electronic security systems, and more particularly to a
key-actuated electronic security system employing keys each
constituted by a plurality of electrically resistive elements, the
system being responsive to the receiving of a key having elements
of predetermined resistance.
Generally speaking, electronic lock circuits heretofore have been
of either digital or analog types. The present invention concerns a
lock system of the analog type. Lock systems of the digital variety
typically use binary techniques which, while facilitating the
manipulation of information derived from a key of the system, may
suffer from complexity. Where the manipulation of information is
not of paramount importance, the use of an analog electronic lock
system offers the significant advantage of simplicity while making
possible highly efficient key coding. In an analog system, a
relatively large number of key combinations may be provided while
using relatively few bitting positions for each key.
In electronic lock systems of the analog variety, it has been
previously proposed to use keys having resistively coded elements.
Disclosures of electronic lock systems employing this type of key
may be found, for example, in U.S. Pat. Nos. 3,093,994, 3,134,254,
3,283,550 and 3,518,655. In one type of prior art lock system, a
key is employed which may have either a resistive or capacitive
element (or both) which, if correct in value, is adapted to cause
oscillation of an oscillator at a frequency causing operation of a
reed relay. In another type of lock system, keys having resistive
elements are adapted to be connected with a single bridge circuit
for effecting balancing of the bridge if the key is correct.
Typically, in prior art analog lock systems, there is employed only
a single frequency-responsive or resistance-responsive circuit
operative in response to a key. Thus the range and number of
possible discrete levels of resistance (or capacitance) which can
be used for the element of the key may be limited in number in
order to assure discrimination between different levels of the keys
or because sensitivity of the circuit is limited. Accordingly, the
total number of possible key combinations is relatively small,
restricting the utility of the system. Heretofore, there has been
no provision in prior art systems for different "levels" of keys,
such as master keys, et cetera. In addition, such systems have not
facilitated the use of so-called multiple keying wherein different
keys may each be received at different receptacles but will cause
operation of the same circuitry at a single key-receiving point, or
the use of duplex keying, wherein different keys may be inserted in
the same key receptacle but wherein each key is adapted to cause
operation of different circuitry. Another difficulty which may be
found in the use of such prior art circuitry is that the circuits
may tend to be so sensitive to changes in temperature as to be
unsatisfactory in use. For example, if an oscillator is employed,
its frequency may undesirably shift sufficiently to cause improper
operation with changes in temperature. Or it may be necessary to
resort to complicated temperature-compensating circuitry in order
to effect immunity to changes in temperature. An even more
significant problem encountered in simple bridge-type circuits of
the type described is that they may be easily "picked." For
example, one attempting to defeat the system may utilize simple
measuring techniques to ascertain the value of resistances in the
bridge circuit and thereby determine the resistance needed to gain
entry.
BRIEF SUMMARY OF THE INVENTION
Among the several objects of the invention may be noted the
provision of an electronic key-actuated security system; the
provision of an electronic key-actuated security system of the
analog type employing keys each constituted by a plurality of
electrically resistive elements; the provision of such a system
wherein each resistive element of a key may have one of many
possible discrete levels of resistance; the provision of such a key
wherein the resistance of an electrically resistive element of the
key may vary from a few ohms to many megohms in value; the
provision of such a system wherein there is an extremely high
number of total possible key codes, i.e., number of combinations of
resistance levels of the resistive elements of keys; the provision
of such a system wherein keys may be provided of several different
levels such as master, grand master, great grand master, etc.; the
provision of such a system wherein multiple keying may be used; the
provision of such a system wherein duplex keying may be used; the
provision of such a system providing great sensitivity to
differences in values of resistance elements of keys of the system,
assuring accurate discrimination between keys; the provision of
such a system which is relatively immune to changes in temperature
over a wide range; the provision of such a system which is
exceedingly difficult to defeat or "pick;" the provision of such a
system which is reliable, long-lasting and highly efficient in
operation; the provision of such a system which is easily and
economically manufactured; and the provision of a key for such a
system which is adapted for bilateral insertion in key-receiving
means of the invention. Other objects and features will be in part
apparent and in part pointed out hereinafter.
Briefly, the present invention involves the provision of apparatus
for use in an electronic key-actuated security system including
keys each constituted by a plurality of electrically resistive
elements. Key-receiving means is provided including conductors for
providing connections with resistive elements of a key received.
The apparatus further comprises a plurality of bridge circuits each
associated with one of the resistive elements of a key received,
each of the bridge circuits having first, second and third
impedance arms. The key-receiving means is adapted to connect a
respective one of said resistive elements as a fourth impedance arm
of each bridge circuit. The first and second impedance arms define
a first preset impedance ratio and the third and fourth impedance
arms define a second impedance ratio. Each bridge circuit is
adapted to be electrically balanced when these ratios are equal. A
differential-input voltage comparator associated with each of said
bridge circuits has an output which is a function of said ratios.
Logic gate means is responsive to the output of each of the voltage
comparators for supplying an output signal when said ratios are
equal for each of the bridge circuits. Electrically actuatable
means such as a latch is responsive to this output signal for
indicating thereby the receiving of a key having resistive elements
of respective resistance values causing balancing of all of the
bridge circuits.
A key for the system comprises an electrically nonconductive member
having a portion adapted for insertion in the key-receiving means,
this portion having an axis of symmetry extending in the direction
of insertion thereof in the key-receiving means. There are pairs of
electrically conductive contacts on the nonconductive member, and
individual electrically resistive elements connected respectively
across the pairs of contacts. The two contacts of each pair are
bilaterally symmetrical with respect to said axis of symmetry
whereby the key is adapted for bilateral insertion in the
key-receiving means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic circuit diagram of an electronic
lock system of the present invention, illustrated as controlling an
electric latch;
FIG. 2 is a detailed schematic circuit diagram of the system of
FIG. 1;
FIGS. 3 and 4 are perspective views of two respective key
embodiments of the present invention, each having a plurality of
resistive elements;
FIG. 5 is a schematic circuit diagram of portions of a system of
the type shown in FIG. 1 and adapted to provide so-called multiple
keying;
FIG. 6 is a schematic circuit diagram of portions of the circuitry
of the type shown in FIG. 1 adapted to provide so-called duplex
keying;
FIG. 7 is a schematic circuit diagram, partly in block-diagrammatic
form, showing circuitry for providing alarm signalling in response
to use of an improper key; and
FIG. 8 is a circuit somewhat similar to FIG. 7 showing a different
type of alarm circuit for providing alarm signalling in response to
insertion of an improper key.
Corresponding reference characters indicate corresponding parts
throughout the several views of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, an electronic key-actuated security system
of the present invention includes a key 11 having a plurality of
electrically resistive elements, such as resistors incorporated
therein, with which electrical connection is adapted to be made by
contacts along opposite edges 13 and 15 thereof. A key receptacle
17 includes an aperture 18 adapted to receive the key and which has
suitable contacts serving as conductors which provide electrical
connections with the resistive elements of key 11 when the key is
inserted and thereby received by receptacle 17. If key 11 is a
correct key, an electric strike or latch 19 is adapted to be
energized to permit opening of a door or the like.
Interconnected with receptacle 17 are a pair of bridge circuits 21a
and 21b, each of which is associated with one of the resistive
elements of key 11. Each of bridges 21a and 21b includes a first
impedance arm provided by a first resistor 23a, 23b, a second
impedance arm provided by a second resistor 25a, 25b, and a third
impedance arm provided by a third resistor 27a, 27b, the latter
constituting code-change resistors.
A respective resistance element of key 11 is connected by
receptacle 17 when key 11 is received therein as a fourth impedance
arm of each bridge. For this purpose, a pair of leads 29a, 31a
connects bridge 21a with receptacle 17 and a pair of leads 29b, 31b
connects bridge 21b with receptacle 17.
The junctions of the respective leads 29a, 29b and respective
resistors 23a, 23b are each connected to a suitable source of
power, designated +V, as shown. The opposite junctions of each
bridge, i.e., between respective resistors 27a, 27b and respective
resistors 25a, 25b, are each grounded. Accordingly, the pairs of
resistors 23a, 25a and 23b, 25b each define a first preset
impedance ratio for each bridge and the pairs constituted by the
resistive elements of key 11 and associated code change resistors
27a and 27b define a second impedance ratio. Each of bridges 21a
and 21b is adapted to be electrically balanced when these
respective first and second impedance ratios are equal, as is
known.
Connected across each bridge by a pair of leads is a respective
voltage comparator 33a, 33b. These comparators are each
differential amplifiers of the differential-input, balanced
differential output type and which have a pair of differential
input terminals and a pair of differential output terminals. The
comparators 33a, 33b may advantageously be monolithic linear
integrated-circuit differential amplifiers which are commercially
available. The potentials at the output terminals of each
comparator 33a, 33b are of predetermined equal level when the
levels of potentials applied to the input terminals thereof have a
predetermined relationship. In accordance with this invention, this
predetermined relationship, which may be constituted by equal
potentials of a fixed or predetermined value, is selected as
indicative of the balancing of the respective bridge. If the
resistive elements of key 11 are of the respective resistance
levels causing balancing of both of the bridges 21a, 21b, key 11
may be said to be a proper key for the system.
Preferably, resistors 27a, 27b are each readily changeable. By
changing resistors 27a, 27b, a different key, i.e., one having
different resistor elements, must then be used to cause balancing
of both bridges 21a, 21b. Thus resistors 27a, 27b constitute key
code changing impedances. For example, these resistors 27a, 27b may
each be constituted by a potentiometer or may instead be
incorporated in a plug which may be readily removed, thereby to
permit replacement with a resistor of different value. The
changeable nature of resistors 27a, 27b is shown by the rectangular
symbols employed for these resistors throughout the drawings.
Balancing of each bridge 21a, 21b is detected by respective
two-input AND gates 35a, 35b. Each AND gate has its two inputs
connected across the differential output terminals of the
respective voltage comparator 33a, 33b. These AND gates 35a, 35b,
which are preferably of the integrated circuit variety widely
available, are each adapted to supply, in effect, an output signal
or intermediate signal when potentials of predetermined equal
magnitude are applied concurrently to the two input terminals
thereof. Such an output signal may be said to be supplied when, in
reality, the output of the AND gate switches from a "low" to a
"high" state, as is known in the electronics arts.
Voltage comparators 33a, 33b are chosen to have sufficient gain
such that, when the respective bridge 21a, 21b is balanced, the
potentials at the output terminals of the comparator are each of a
level which is sufficient to cause the respective AND gate 35a, 35b
to deliver an output signal, thereby indicating balancing of the
respective bridge.
A further two-input AND gate 37 has each of its input terminals
connected with the respective output terminal of AND gates 35a,
35b. Thus, when each of the latter gates delivers an output signal
(i.e., goes "high"), AND gate 37 delivers an output signal which is
indicative that both of bridges 21a, 21b are balanced.
It should be understood that additional bridges may be employed,
each having a voltage comparator connected thereacross and an AND
gate connected across the differential output of the comparator,
all as described above. In such case, key 11 may have additional
resistive elements each of which is connected as an arm of an
additional bridge by receptacle 17. If such additional bridge
circuits are employed, AND gate 37 would have additional inputs as
necessary corresponding to each such additional circuit so that
this AND gate will provide an output signal when all of the bridges
are balanced.
The output terminal of AND gate 37 is interconnected with the gate
or triggering electrode of a triggerable semiconductor switching
device constituted by triac 39 whose main terminals are connected
in a circuit with latch 19 between a suitable source of power, such
as 112 v.a.c., and ground. When AND gate 37 delivers an output
signal, triac 19 is triggered to cause energization of latch 19
thereby to permit opening of the door or the like secured by the
latch.
Without the use of amplifying devices, such as a voltage
comparator, for the purpose of providing gain, relatively few
discrete levels of resistance can be measured using a bridge
circuit. For that reason, amplification is desirable. Although
amplification has been previously employed in connection with lock
systems utilizing a bridge which measures the resistance of a key
element, conventional single-ended amplifiers are not readily
temperature-compensated. Or at best, limited compensation is
possible, e.g., 4,000 parts per million per degree centigrade.
On the other hand, differential amplifier voltage comparators of
the type described herein, providing temperature compensation of
high order over a great range of temperatures, may be readily
obtained. Further, the incorporation of such devices provides
sufficient amplification or gain to permit the resistance of key
resistive elements to range from a few ohms to several megohms in
value. Accordingly, ordinary commercially-available resistors may
be employed. Each resistive element of a key of the present system
may, therefore, be selected from over 100 discrete resistance
levels, allowing wide margin for error. Further,
commercially-available resistors for use as key elements may be
obtained which provide temperature compensation as great a degree
as desired.
Since each key resistive element may have resistance of at least
approximately 100 levels, the total number of possible key codes or
combinations is given approximately by 100.sup.n, where n is the
number of individual resistive elements which are each connected to
a bridge of the system. For example, if four resistive elements are
used, providing four so-called bitting positions, the lock or
security system provides (100).sup.4, i.e., 10.sup.8, resistance
combinations.
A further advantage in using integrated circuit voltage comparators
of the type described is that the system is thereby relatively
immune to changes in supply voltage. Also, the system is not
appreciably affected by aging of components.
A practical embodiment showing specific circuitry is shown in FIG.
2 wherein a key is illustrated as having two resistive elements
41a, 41n which may be two of several such elements 41a, 41b, . . .
, 41n, et cetera. Elements 41a, 41n are adapted to be
interconnected by receptacle 18 with respective bridge-voltage
comparator circuits 49a, . . . , 49n, et cetera.
Circuits 49a, 49n are essentially identical and each is, in effect,
a combined bridge and voltage comparator. Circuit 49a includes
first and second impedance arms provided by resistors 23a and 25a,
respectively, connected in a series circuit between a positive d.c.
supply potential and ground. A key code changing impedance is
constituted by a resistor 27a which is either a potentiometer or is
readily removable to permit its replacement by a resistor of
another value, as described hereinabove. Key resistive element 47a
provides a fourth impedance arm of the bridge. Resistor 27a and
element 47a similarly are series-connected between the positive
supply and ground. Resistive element 47n provides a fourth arm of a
bridge of circuitry 49n, et cetera.
Resistive element 47a and code changing resistor 27a together
provide a voltage divider, the potential at their junction being a
function of their respective impedance or resistance values. The
same is true of interconnected resistors 23a and 25a, whose
junction provides a potential which is fixed and thus serves as a
reference potential. These two junctions serve as opposite nodes of
the bridge, and across which is connected a differential-input
voltage comparator.
The latter voltage comparator includes a pair of PNP transistors Q1
and Q2 whose emitters are connected via respective resistors R1 and
R2 to a common emitter resistor R3, thence to the positive supply
potential. Respective load resistors R4 and R5 connect the emitters
of Q1 and Q2 to ground. The bases of transistors Q1 and Q2 are each
connected through a respective diode D1 and D2 to one node of the
bridge and thus will be more or less conductive according to the
difference between the node potentials, one transistor becoming
more conductive as the other becomes less conductive, and vice
versa.
Connected to the top of each of resistors R4 and R5 is the
respective base electrode of one of two further transistors Q3 and
Q4, each of which has its collector and emitter terminals connected
in a series circuit, including a respective collector load resistor
R6, R7 between the positive supply potential and ground.
The two input terminals of AND gate 35a are each connected to the
junction of one of these resistors R6, R7 and the respective
collector of transistors Q3, Q4. These latter junctions constitute
balanced differential output terminals of the voltage comparator
whose potentials are of predetermined equal level when the levels
applied to the input terminals of the comparator (i.e., the
aforesaid opposite nodes of the bridge) have a predetermined
relationship defined by balancing of the bridge (the potentials at
these nodes then being equal). The output of AND gate 35a goes
"high" thereby delivering, in effect, an output signal when the
predetermined equal output potentials of the voltage comparator
(which are present when the bridge is balanced) are delivered to
the input terminals of this AND gate. The same operation occurs as
to the circuitry 49n as well as any other bridge-voltage comparator
circuits of the system.
The several AND gates 35a, . . . , 35n, etc., have their output
terminal connected to the input terminals of AND gate 37 whose
output terminal, as explained, delivers an output signal when all
of the several bridges are balanced.
From the foregoing, it may be seen that AND gates 35a, . . . , 35n,
etc., as well as AND gate 37, together constitute logic gate means
connected to the output terminals of the voltage comparators and
which provide an output signal when the potentials at each pair of
comparator output terminals are each of predetermined equal level
indicative of bridge balancing.
The output terminal of AND gate 37 is interconnected with the gate
electrode of triac 39, whose main electrodes are connected in
series with a solenoid 51 of latch 19 across the secondary winding
of a step-down transformer 53. This secondary winding also supplies
a suitably low voltage which is rectified by a diode D3 to provide
+9 v.d.c. for each of the bridge-voltage comparator circuits 49a, .
. . , 49n, etc., and, by means of a zener diode D4 and transistor
Q5 conventionally controlled thereby, well-regulated +5 v.d.c. for
operation of the several AND gates.
An output signal from AND gate 37 therefore causes triggering of
triac 39 to effect operation of solenoid 51 of latch 19, thereby
permitting the door, etc., otherwise locked by latch 19 to be
opened. Alternatively, latch 19 may be substituted for by signal
means having a light or buzzer, etc., in place of solenoid 51, or
by interface with desired electrical apparatus. In any case, latch
19 constitutes one type of suitable electrically actuatable means
responsive to the output signal from AND gate 37 for indicating, by
its operation, the receiving of a key having resistive elements of
resistance values causing balancing of all the bridges.
Naturally, the system may be designed to operate a door latch that
will respond to relatively low voltage, and operation of the system
then may be obtained through use of batteries where that is
desired, such as in the case of an emergency or power failure.
In order to provide additional assurance against "picking" or
illicit decoding, a security system of the present invention may
have bridges each of which has impedance arms which define
different impedance ratios as between the several bridges. Thus the
reference potential defined by the pair of series-connected fixed
resistors described above may vary from bridge to bridge or from
system to system thereby greatly increasing the difficulty in
attempting to illicitly measure by electronic techniques the fixed
and code-setting resistances of each bridge. One who somehow
ascertains such values at one key-receiving station would,
accordingly, not be able to utilize such information to gain access
at other key-receiving stations.
Referring to FIG. 3, a key like that shown in FIG. 1 is similarly
designated generally 11. The key includes a relatively flat, thin
electrically nonconductive member 53 of tapered form having side
edges 13 and 15 converging toward one another toward a narrow,
rounded nose portion 55 adapted for insertion in aperture 18 of
receptable 17. Member 53 may be of a suitable resilient synthetic
resin material such as employed in printed circuit board
construction. As is apparent, nose portion 55 has an axis of
symmetry shown as a dotted line 56 extending in the direction of
insertion in receptacle 17. There are pairs of electrically
conductive contacts on the surface of member 53 and which are
designated 57a, 57b; 59a, 59b; 61a, 61b; and 63a, 63b. Each of the
a contacts is located on the face of member 53 adjacent edge 13 and
the b contacts are similarly located adjacent edge 15. The two
contacts of each pair are bilaterally symmetrical with respect to
the axis of symmetry 56 of portion 55, i.e., the two contacts are
each the same distance along a line perpendicular to the axis of
symmetry.
Individual electrically resistive elements 47a, 47b, 47c and 47d
are connected respectively across the pairs of contacts 57-63.
Elements 47a-47d are concealed, molded or otherwise positioned in a
somewhat thicker, generally rectangular handle portion 67 of the
key. These elements 47a-47d are each connected by pairs of thin,
flat strips extending back from the pairs of contacts 57-63 on the
surface of member 53 and which are integral with the respective
contacts. These strips may, for example, be provided by utilizing
printed circuit techniques involving etching of metallic cladding
on member 53 according to a suitable pattern. Elements 47a-47d may
be individual miniature resistors or may be provided through use of
suitable thick film techniques or the like. Of course, while four
resistive elements are shown, the key may have a greater or lesser
number of elements, as appropriate. Also, some of the elements,
e.g., two of them, may be adapted to be interconnected with
circuitry at a particular receptacle for unlocking a door, etc., at
that location while another set of elements of the key may be
adapted to unlock yet another door at some other location or
locations.
The symmetry of contacts 57-63 provides an important advantage in
that the key is not "handed," i.e., it is adapted for bilateral
insertion in receptacle 17. Not only is this a great convenience,
but if the system includes an alarm which operates in response to
insertion of an improper key, such a symmetric key avoids alarm
signalling which might occur if an asymmetrical key were inserted
with improper orientation.
In order to assure that each of resistive elements 47a-47d will be
positively interconnected when the key is inserted in receptacle
17, there may be pairs of contacts on the opposite side of the key
which are identical with those on the front as shown. There is then
a redundant set of contacts and electrical connection is thus
maintained even if one contact should fail to make a good
connection.
In FIG. 4, another embodiment of a key of the system is designated
generally 69 and includes a nonconductive member 71 of generally
rectangular shape having a straight edge or nose portion 73 adapted
for insertion in a suitable receptacle. Five electrically
conductive contacts 75a-75e are located on the flat surface of
member 71 adjacent the edge or nose portion 73. Contacts are thin
and flat, and may be of metallic cladding such as used in printed
circuit board construction. Extending back from contacts 75a-75e,
away from edge 73, are thin, flat strips 77a-77e, each of which is
integral with its associated contact. Each of strips 77a-77d is
connected, as illustrated, to one side of one of four resistive
elements 47a-47d which are molded or otherwise positioned in a
somewhat thicker, generally rectangular handle portion 79 of the
key, as in the key of FIG. 3.
Strip 77e constitutes a common or "return" lead which is connected
to one side of each of resistive elements 47a-47d and thus contact
75e associated with strip 77e together with each of contacts
75a-75d provides pairs of contacts which are adapted to provide
connection of the resistive elements 47a-47d with individual bridge
circuits of a system of this invention when the key is inserted in
a receptacle.
By varying the position of the "return" contact as between
different receptacles and keys, the use of keys having a particular
"return" contact location can be excluded and thus recoding can be
effected without changing the values of key resistive elements to
which the individual circuits of the system will respond. For
example, the "return" contact may instead be the middle contact
75c, so that only keys having this configuration will cause
operation of circuitry of the system.
FIG. 5 shows circuitry providing so-called multiple keying in which
a single voltage comparator and logic AND gate combination is
responsive to either one of two different key resistive elements
connected by means at respective different sets of receptacle
contacts or received at receptacles which are at different
locations.
A first pair of receptacle contacts is designated 79a and a second
pair of receptacle contacts is designated 79b. Pairs of contacts
79a and 79b may be located in the same receptacle, such as
receptacle 17 of FIG. 1, or may instead be at different receptacle
locations. The pair of contacts 79a is adapted to provide
interconnection with a resistive element 47a of a key and the pair
of contacts 79b provides interconnection with a resistive element
47b.
Voltage comparator 33 has its differential output terminals
connected to the input terminals of AND gate 35, as in FIGS. 1 and
2, and the output terminal of the latter is connected to one input
of a further AND gate as previously described. It should be
understood that the system includes at least one other
comparator-AND gate combination associated with a bridge circuit,
etc., with which is connected some other resistive element (not
shown) of the key when the key is inserted.
The circuitry shown includes a first voltage divider constituted by
code-change resistor 27a and resistive element 47a, which is
connected with resistor 27a and with the voltage source, designated
+V, when the key is inserted so as to provide, at the junction of
resistor 27a and element 47a, a first potential whose level is a
function of these two impedances or resistance values. This
potential is applied to one input of comparator 33 through an
isolation diode D5a.
Another voltage divider connected between the voltage source +V and
ground is constituted by resistors 23 and 25 whose junction
provides a predetermined reference potential to the other input
terminal of comparator 33.
If, when the key is inserted, resistive element 47a has a "correct"
value, the potentials applied to the input terminals of comparator
33 will have a predetermined relationship, e.g., they are of a
predetermined equal level, and consequently the output terminals of
the comparator will provide output potentials of predetermined
equal level causing AND gate 35 to deliver an output potential
thereby indicating that key element 47a is correct.
If key element 47b is connected, then a voltage divider is
similarly constituted by a code-change resistor 27b and element 47b
so as to provide at their junction a potential whose level is a
function of these two resistances. This potential is applied to the
first said input terminal of comparator 33 through an isolation
diode D5b.
Accordingly, regardless of which of elements 47a or 47b is
connected, operation is the same and it will be apparent that the
same circuitry responds to different key-resistive elements. This
makes possible not only the use of master keys but also facilitates
the separate location of a plurality of receptacles, each of which
may be connected to a single circuit.
Those skilled in the art will recognize that the various resistors
23, 25 and 27, and appropriate key element 47 comprise a bridge
circuit as previously described, the arms on one side of the bridge
depending upon which of elements 47a or 47b is connected. It will
be apparent that key elements additional to those shown can also be
connected using the principles of FIG. 5.
In FIG. 6, circuitry is illustrated which provides so-called duplex
keying in which a single pair of key receptacle contacts 79 is
adapted to provide connection of one of a plurality of
key-resistive elements 47a and 47b for the purpose of causing
operation of different comparator-AND gate circuit
combinations.
A first combination of voltage comparator 33a and AND gate 35a is
adapted to supply an output signal in response to a predetermined
resistance value of key element 47a and a second combination
including a comparator 33b and AND gate 35b is adapted to supply an
output signal in response to a predetermined resistance value of
key element 47b. The junction of code-change resistor 27 and
whichever of key elements 47a or 47b is connected provides a first
potential to one input terminal of each of comparators 33a and 33b.
The other input terminal of each of these two comparators is
provided with a different preselected reference potential by a
voltage divider including resistors 23a, 23b and 25
series-connected between the voltage source +V and ground.
Accordingly, if either of comparators 33a or 33b is provided with
input potentials of proper predetermined relationship, the
associated AND gate 35a or 35b will provide an output potential or
signal. It will be understood that a system of the invention may
include several circuits like that shown in FIG. 6 with each
connected to supply an input signal to a multi-input AND gate such
as AND gate 37 of FIG. 1.
This circuitry is highly advantageous in permitting the use, in a
lock system of this invention, of various levels of keys including
so-called change keys, master keys, grand master keys, and so
forth. To this end, a single pair of contacts 79 may be connected
to several comparator-AND gate circuit combinations, each such
combination being operative in response to a different level of
keying.
A security system of the present invention may be provided with an
alarm signal or the like operative in response to the insertion of
an incorrect key. Accordingly, a guard may be called or a
photograph may be taken of the individual attempting to use an
incorrect key. Referring to FIG. 7, the key receptacle 17 may be
provided with a microswitch or the like having a set of normally
open contacts 81 adapted to close when the key 11 is inserted in
receptacle 17. Contacts 81 may be connected in a circuit with a
voltage source, as indicated, so as to provide, when closed,
voltage to the various system circuits 83 (such as shown in FIG. 2)
via a lead 87. The circuitry 83 is shown to have a lead 85
providing an output signal for operation of a latch in response to
insertion of a "proper" key. The winding of a relay 89 is shown
connected between lead 85 and ground, and this is adapted for
energization by the output signal causing latch operation. Relay 89
is shown to include a set of normally closed contacts 89K connected
in circuit between switch contacts 81 and one side of a time delay
circuit 91. The latter may comprise a conventional time delay relay
or the like adapted to close a circuit after a predetermined time
delay interval following energization thereof. For this purpose,
the other side of time delay circuit 91 is connected to an alarm
bell 93 or other suitable alarm signalling means, one terminal of
which is grounded.
In operation, insertion of key 11 closes contacts 81 to energize
the system circuits 83 for normal operation and to energize time
delay circuit 91. If time delay circuit 91 is not deenergized by
operation of relay 89 in response to an output signal on lead 85,
delay circuit 91 will complete a connection between contacts 89K
and alarm bell 93 to give an aural alarm. The alarm signal thus
provided may be used for any suitable purpose. If a proper key is
inserted, the resultant output signal on lead 85 will energize
relay 89 to prevent operation of the alarm 93.
In FIG. 8, alarm circuitry of another embodiment is illustrated.
This embodiment includes a logic OR gate 95 having a plurality of
input terminals each interconnected with a respective one of the
output terminals of the voltage comparators 33a, 33b, etc., of the
system. The output terminal of OR gate 95 is connected to one input
of an AND gate 97 having another input terminal (shown as an
inverted-input terminal) which is connected to output signal lead
85 of the system circuitry (by means of which lead an output signal
causing latch operation is provided). The output terminal of AND
gate 97 is connected to time delay circuit 91 of the type described
above, which is in turn connected to alarm bell 93 or other
suitable alarm signalling means.
If any of comparators 33a, 33b, etc., provides an output signal in
response to connection of a key-resistive element, even if of an
improper value, the resultant input signal to OR gate 95 will cause
the latter to provide an input signal to AND gate 97. If no output
signal is provided on lead 85, AND gate 97 will supply an output
signal energizing time delay circuit 91. After a predetermined time
delay, alarm bell 93 will be energized. However, insertion of a
proper key will provide a signal on lead 85 which will cause there
to be no output potential from AND gate 97, and thus operation of
alarm 95 will be prevented.
It may be noted that a system of this invention facilitates the
making of a permanent record of the use of keys. Because the system
may be designed to respond to keys whose resistive elements are
differently coded, the keys may be used for identification purposes
and a conventional print-out ohmmeter may simply be connected with
a key receptacle to make a printed record of the resistance values
of keyresistive elements from which it may later readily be
determined which individuals have used their keys.
In general, a high level of security is provided by a system of the
invention and this is enhanced by the fact that duplication of keys
is relatively difficult.
In view of the above, it will be seen that the several objects of
the invention are achieved and other advantageous results
attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it is intended that all
matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
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