US3717795A

US3717795A - Code-responsive control circuit

Info

Publication number: US3717795A
Application number: US00170484A
Authority: US
Inventors: C Atkins
Original assignee: Wagner Electric Corp
Current assignee: Cooper Industries LLC
Priority date: 1971-08-10
Filing date: 1971-08-10
Publication date: 1973-02-20
Anticipated expiration: 1990-02-20

Abstract

A control circuit operative to change the energization state of a controlled device (e.g., a relay) only in response to the momentary closing of a series of charging/discharging circuits in a predetermined sequence, in which sequence the first path closed is also the last path closed. Control of the charging/discharging circuits is preferably effected by a group of symbol-bearing, pushbutton-actuated switches, including several penalty switches which are not part of the combination and which will ''''erase'''' the effect of previously-actuated combination switches if actuated at an intermediate stage of the combination sequence.

Description

United States Patent [191 Atkins 1 Feb. 20, 1973 [54] CODE-RESPONSIVE CONTROL CIRCUIT [75] Inventor: Carl E; Atkins, Montclair, NJ. [73] Assignee: Wagner Electric Corporation,

Newark, NJ.

[22] Filed: Aug. 10, 1971 [2]] Appl. No.: 170,484

[52] US. Cl. ..3l7/l34, 317/1485 R [51] Int. Cl. ..E05b 49/00 [58] Field of Search ..3l7/l34, 148.5 R, 151

[56] References Cited UNITED STATES PATENTS 3,522,488 8/1970 Tellerman ..3l7/l34 3,242,388 3/1966 Tellerman ..317/151 X 3,428,033 2/1969 Watts ..317/134 X Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney-William D. Lucas et a1.

[57] ABSTRACT A control circuit operative to change the encrgization state of a controlled device (e.g., a relay) only in response to the momentary closing of a series of charging/discharging circuits in a predetermined sequence, in which sequence the first path closed is also the last path closed. Control of the charging/discharging circuits is preferably effected by a group of symbol-bearing, pushbutton-actuated switches, including several penalty switches which are not part of the combination and which will erase" the effect of previously-actuated combination switches if actuated at. an intermediate stage of the combination sequence.

10 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Code-Responsive or Secret (e.g., door lock) Electric Circuitry for controlling relays, electromagnets, and the like, found in Class 317, Subclass 134.

2. Description of the Prior Art Various forms of code-responsive circuitry exist in the prior art. For example, U. S. Pat. No. 3,242,388 issued on Mar. 22, 1966 upon an application filed in the name of Edward Tellerman discloses several circuits which are operative to release a locking mechanism only for an adjustable period of time, e.g., long enough to permit opening of a previously locked door, after which the release mechanism is automatically rendered inoperative.

U. S. Pat. No. 3,522,488 issued on Aug. 4, I970 upon an application filed in the name of Edward M. Tellerman discloses improvements on the earlier Tellerman patent, this improvement being embodied in a circuit in which all of the pushbuttons in the array, i.e., those which are part of the code combination and those which are not, must be actuated in one of two ways: either the code buttons are actuated in the ordained sequence followed by actuation of all of the buttons in the array, or the code buttons are actuated in the ordairied sequence followed by actuation of all of'the buttons which are not involved in the code combination. The purpose is to foil unauthorized persons who might ascertain which buttons are code buttons by dusting all of the buttons with a fingerprint-detecting chemical after use by an authorized person. However, this approach obviously involves considerable inconvenience and delay for the authorized user, who must push an excessive number of buttons to actuate the control circuit.

U. S. Pat. No. 3,555,510 issued on Jan. 12, 1971 to Tore Gottfrid Hesselgren discloses a circuit in which the charging of one capacitance controls the current path of a subsequent capacitance by rendering conductive a transistor connected in that charging path. Such an arrangement involves the use of transistors in the charging circuits for the plurality of capacitances employed (except the first capacitance), and is therefore disadvantageous from the point of view of cost. Also, this circuit is operative to energize a relay only momentarily, in the manner of the Tellerman patents discussed earlier.

SUMMARY OF THE INVENTION Applicants invention is embodied in and carried out by a code-responsive control circuit which is operative to change the energization state of a load and to maintain the load in its new energization state until power is removed from the circuit. This is accomplished when the code sequence is carried out, in which sequence the first step is repeated as the last step, i.e., the first pushbutton actuated must be again actuated as the last step in the code sequence. This represents a new approach to the problem of thwarting an unauthorized person who employs dusting to learn which pushbuttons are employed in the code combination. Even though this information may be determined by this technique, the unauthorized person would most likely assume that the number of steps in the code combination is equal to the number of buttons pushed by the authorized user. With regard to applicants invention, he would be wrong in making such an assumption, since the code combination always involves one step more than the number of buttons employed in carrying out each step.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the present invention, reference should be made to the accompanying drawing, which is a schematic diagram of the circuit which is the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, the circuit schematically illustrated is designed to be powered by a source E- having a nominal output voltage of +12 volts DC applied between terminals 10 and 12. The application of such DC power between terminals 10 and 12 is advantageously controlled by a variety of means, e.g., the insertion of a key into a circuit-controlling lock S without regard to the position or setting of the lock in an automotive application of the invention. When the circuit is thus suitably powered, the voltage between the terminals 10 and 12 will be impressed across the voltage divider formed by resistances 14 and 16, but the diodes 18, 20, 22 and 24 will prevent charging of capacitances 26, 28 and 30 from the voltage divider. When switch 32 in the group of combination switches 32, 34 and 36 is actuated, i.e., when the armature thereof is momentarily moved leftward to close with the normally-open contact which is connected through resistance 38 to the power source, capacitance 26 is charged. Then, when combination switch 34 is momentarily closed after the armature of switch 32 has returned to its normal position as shown, capacitance 28 is charged from capacitance 26. Then, when combination switch 36 is momentarily actuated after switch 34 has returned to its normal open position as shown, capacitance 30 is charged by capacitance 28. At this point in the combination sequence, the positive voltage across capacitance 30 is applied to the base of transistor 40, which is cascaded with transistor 42 by having the emitter of the former connected to the base of the latter, with the collectors of both being connected directly to the hot terminal 10, to form a high input impedance and thus prevent the too-rapid discharge of capacitance 30. The normally-

non-conductive transistors

40 and 42 are rendered conductive, thereby partially closing a current path through the collector-emitter junction of transistor 42, current-limiting resistance 44, and the collector-emitter junction of' transistor 46, which are connected in series between terminals 10 and 12. Consequently, input current flows across the base-emitter junction of transistor 52, rendering its collector-emitter junction conductive with the result that current flows through series-connected resistances 54 and 56 and said junction. Capacitance 58 is connected from the junction of re sistors 54 and 56 to ground in order to prevent switching circuit 62, 64 from being rendered conductive by transients occurring when power is applied to the control circuit. Since the collector of transistor 52 is now negative-going, switching circuit 62, 64 will remain non-conductive. Transistor 46 also remains in its normallyenon-conductive state until combination switch 32 is actuated a second time, thereby causing charging current to flow again from the power source through resistance 38 and the switch 32 to partiallydischarged capacitance 26 and through resistance 27 to ground. Thus, a pulse is developed at the junction of capacitance 26 and resistance 27, and this pulse is fed through capacitance 48 to the base of transistor 46, which is connected to ground through-resistance 50. Thus, transistor 46 is pulsed conductive, thereby momentarily completing the current path through transistor 42, resistance 44 and transistor 46. The negative-going pulse thus developed at the collector of transistor 46 is applied to second-stage transistor 52, which in turn develops an amplified, positive-going pulse at its collector. This output pulse of transistor 52 is fed through capacitance 60 to the control or gate electrode of the switching circuit formed by complementary transistors 62 and 64 connected in the regenerative feedback configuration. This switching circuit 62,64 is normally biased non-conductive by circuit 80, but when it is turned on by the application at the gate electrode of a positive pulse sufficiently large to overcome the negative DC bias, will remain conductive in spite of that bias after the pTzlse is terminated so long as a current greater than the extinction current of the switching circuit 62, 64 continues to flow from anode to cathode, i.e., from the emitter of transistor 62 to the emitter of transistor 64. When switching circuit 62, 64 is rendered conductive by the positive pulse developed at the emitter of transistor 52 and fed through capacitance 60 to the control or gate electrode (base of transistor 64/collector of transistor 62), the direct-current path through'load L and the switching circuit 62, 64 is closed. Consequently, the normally-deenergized load L (a relay or solenoid, for example) connectqd between output terminals 70 and 72 is energized,'-. and will remain energized so long as power is applied between terminals and 12. Capacitance 66 and resistance 68 connected in series between the anode and cathode of switching circuit 62, 64 prevent accidental firing of the switching circuit 62, 64 by transients which occur when power is applied to the control circuit, i.e., when switch S is closed. When switch S is re-opened, capacitances 26, 28 and 30 discharge through resistance 16 and the intermediate diodes.

Parallel-connected penalty switches 74, 76 are connected as a group in series with current-limiting resistance 78 from ground to the cathodes of diodes and 22, and to the anode of diode 24 which isolates the discharge circuits afforded the penalty switches from the positive voltage at the junction of voltage-divider resistances 14 and 16. Without diode 24, the closing of any penalty switch would place resistance 78 in parallel with resistance 16, and the desired discharge of capacitances 28 and 30 through diodes 20 and 22, respectively, would not be accomplished since the cathodes of diodes 20 and 22 would be placed at a reduced positive potential rather than at ground potential. In the arrangement shown, the capacitances 28 and 30 will be virtually completely discharged if any penalty switch is closed. Discharge of capacitance 26 may also be accomplished upon closing of any penalty switch if the cathode of diode 18 is connected to the anode (instead of the cathode) of diode 24. Any number of parallel-connected penalty switches may be utilized, and actuation of any penalty switch will erase the effect of previously-actuated combination switches, thereby making actuation of load L by an unauthorized person extremely difficult and unlikely.

The bias circuit 80 which provides approximately -5 volts DC through resistance 82 to the gate electrode of switching circuit 62, 64 comprises an oscillator comprising transistor 84, the base of which is connected to the power source through resistance 86. The emitter of transistor 84 is grounded, and its collector is connected to the source of power through an LC network comprising a pair of inductances 88 and 90 both connected at one terminal to the power source via terminal 92, with a capacitance 94 being connected between the other two terminals of the inductances. The feedback signal required for oscillation is derived at the junction of inductance 90 and capacitance 94, and is fed back through capacitance 96 to the base of transistor 84. The oscillatory output is derived at the junction of re sistance 98 and capacitance 100 connected in series between the collector of transistor 84 and ground. This output is rectified by diode 102, and the rectified output is impressed across the averaging network formed by capacitance 104 and resistance 106 connected in parallel; this averaging network is connected from ground in series with res istance 82 to the gate electrode of switching circuit 62, 64.

In the preferred embodiment disclosed herein, the values of the various circuit elements are as follows:

The advantages of the present invention, as well as certain changes and modifications of the disclosed embodiment thereof, will be readily apparent to those skilled in the art. It is the applicants intention to cover all those changes and modifications which could be made to the embodiment of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.

What is claimed is:

1. A code-responsive control circuit comprising:

1. signal circuit means comprising a plurality of switching means which must be momentarily actuated in a predetermined sequence in which momentary actuation of a single, predetermined switching means must be repeated as the last step of said sequence, said signal circuit means being operative in response to the momentary actuation of said plurality of switching means in said predetermined sequence to generate an output signal; and

2. load-controlling circuit means operative in response to said output signal of said signal circuit means to change the energization state of a load.

2. A code-responsive control circuit according to claim 1 wherein said signal circuit means comprises first, second and third capacitances, said first capacitance being chargeable by momentary actuation of first switching means, said second capacitance then being chargeable from said first capacitance through de-actuated first switching means and momentarily-actuated second switching means, said third capacitance then being chargeable from said second capacitance directly through momentarily-actuated third switching means.

3. A code-responsive control circuit according to claim 2 wherein said signal circuit means comprises a voltage divider including first and second resistances, and a plurality of diodes connected between the junction of said first and second resistances and said first, second and third capacitances to prevent the flow of charging current from said voltage divider to said capacitances when said control circuit is energized, and to enable the discharge of said capacitances when said control circuit is de-energized.

4. A code-responsive control circuit according to claim 1 wherein said signal circuit means is operative to generate a first intermediate signal when each of said switching means is actuated in said predetermined sequence excepting the repeated actuation of said single, predetermined switching means, and to generate a second intermediate signal when said single, predetermined switching means is actuated a second time, said output signal being generated simultaneously with said second intermediate signal.

5. A code-responsive control circuit according to claim 2 wherein said signal circuit means comprises:

1. first amplifier means having a high input impedance, with its input terminal connected to the high side. of said third capacitance;

2. second amplifier means having first and second stages, the output terminals of said first stage and the input terminals of said second stage both being connected in series with the output terminals of said first amplifier means;

3. a third resistance connected in series with said first capacitance;

. pulse-carrying circuit means connected between the junction of said third resistance and said first capacitance and the input terminal of said second amplifier means.

6. A code-responsive control circuit according to claim 5 wherein said first intermediate signal is provided by said first amplifier means to the input terminal of the second stage of said second amplifier means, and

said second intermediate signal is provided by said first stage of said second amplr ier means to the input of its second stage.

7. A code-responsive control circuit according to claim 1 wherein said load-controlling circuit means comprises:

i. a normally non-conductive switching circuit having gate, anode and cathode terminals, with the load to be controlled connected in series with said anode and cathode terminals; and

2. bias circuit means operative to provide a direct current bias to said gate electrode of said switching circuit.

8. A code-responsive control circuit according to claim 1 wherein said load-controlling circuit means, once having operated in response to said output signal of said signal circuit means to change the energization state of the load, is further operative to maintain the load in that changed energization state until power is no longer applied to said code-responsive control circuit.

9. The code-responsive control circuit according to claim 1, further comprising at least one penalty switch means operative to erase the effects of said switching means which have been previously actuated.

10. The code-responsive control circuit according to claim 1, further comprising lock-switch means operated to cause a source of power to be connected to said control circuit by the insertion in said lock-switch means of a key operative to actuate said lockswitch means.

Claims

1. A code-responsive control circuit comprising: 1. signal circuit means comprising a plurality of switching means which must be momentarily actuated in a predetermined sequence in which momentary actuation of a single, predetermined switching means must be repeated as the last step of said sequence, said signal circuit means being operative in response to the momentary actuation of said plurality of switching means in said predetermined sequence to generate an output signal; and 2. load-controlling circuit means operative in response to said output signal of said signal circuit means to change the energization state of a load.

1. A code-responsive control circuit comprising:

1. first amplifier means having a high input impedance, with its input terminal connected to the high side of said third capacitance;

1. a normally non-conductive switching circuit having gate, anode and cathode terminals, with the load to be controlled connected in series with said anode and cathode terminals; and

3. a third resistance connected in series with said first capacitance;

4. pulse-carrying circuit means connected between the junction of said third resistance and said first capacitance and the input terminal of said second amplifier means.

6. A code-responsive control circuit according to claim 5 wherein said first intermediate signal is provided by said first amplifier means to the input terminal of the second stage of said second amplifier means, and said second intermediate signal is provided by said first stage of said second amplifier means to the input of its second stage.