GB2133232A - Wall switch timing circuit - Google Patents

Abstract

An electronic timing device opens an electrical circuit whenever the circuit, e.g., a lighting circuit, has been left closed accidentally. The device is wired in series with an existing wall switch 13 and the load 12 which it controls. Whenever the existing switch 13 is turned on, a load sensing circuit senses the flow of current and triggers a timing circuit. The timing circuit may be preset to some arbitrary time period. At the expiration of the time period, the timing circuit opens a switch circuit 1 to disconnect the load. The timer assembly is sufficiently compact that it fits within a modified switch plate having a slight recessed area surrounding the switch lever opening (Figs. 3 to 5). Optionally, when the timer times out, the switch 1 may be intermittently closed to give a flashing warning for a predetermined period before the switch 1 is finally opened continuously. An audible warning may alternatively be given. The device may be connected in parallel, rather than series, with the existing switch 13 to function as a turn-off delay. <IMAGE>

Description

SPECIFICATION Wall switch timing circuit Background of the Invention Field: The present invention relates to switching circuits, and more particularly to an electronic circuit for the switching of an AC power line supplying current to lamps or small appliances.

Prior Art: Switches, such as wall switches, are employed to control electrical energy applied to lighting equipment and other relatively small energy consuming devices. A typical wall switch is a toggle switch having a manual actuator with positive "on" and "off" positions. When a toggle switch is turned "on", it remains in that condition until it is manually switched to the "off" position.

Such switches, controlling lights, exemplarily, are frequently left in the "on" position, actuating the lights in a room, exemplarily, even after the room has been vacated. When the user has moved from the area of the switch, he may have forgotten to turn it off. The result is a waste of energy and unnecessary use of the controlled device, shortening its useful life. Previous patents which disclose timing circuits are Cleary, U.S. Patent 4,204,149 and Monahan U.S. Patent 4,002,925.

Objects of the Invention It is therefore an object of the present invention to provide an electronic circuit for the automatic denergization of a power circuit that has been left on inadvertently.

Another object of the present invention is to provide a circuit automatically deenergizing an electrical power circuit controlled by a conventional toggle actuator such as a wall switch.

Another object of the present invention is to provide for the automatic deenergization of household switches after a preset time.

Another object of the present invention is to provide such an electronic switch assembly which is inexpensive and compact enough to be placed in a conventional wall box holding a conventional wall toggle switch.

Another object of the present invention is to provide an additional circuit which may flash the lights by intermittently interrupting the circuit several times or by providing an audible signal before the electronic switch assembly turns off the power.

Summary of the Invention The instant invention comprises an electronic timer sized to adapt to a typical switch box sized for a single toggle switch. The cover plate is a modified plate which provides a slight cavity surrounding the switch lever opening to provide the space necessary to accept the timer assembly.

The modified switch plate containing the timer assembly may be easily substituted for an existing switch plate. Installation requires only two wires from the timer assembly to be connected in series with the existing toggle switch. A plurality of timers may be adapted to fit within a large switch plate which covers a plurality of toggle switches.

The present invention provides for the automatic deenergization of a circuit controlled by an operator manipulated switch at the end of the predetermined time interval. The manually controlled switch has distinct "on" and "off" positions, the circuit associated with the switch being respectively energized or not energized. The present invention deenergizes the circuit even if the manually operated switch remains in the "on" position. When the toggle switch is turned on, a load sensor determines that there is a load in the circuit, starting a timing circuit and actuating a triac to complete the circuit through the toggle switch and load. If the toggle switch is not turned off before the expiration of a predetermined time interval, the triac is turned off upon the expiration of the predetermined time interval, opening the alternating current power circuit.Optionally, a circuit may be provided turning the power off and on a number of times rapidly through the triac, thereby flashing lights and providing a warning to anyone in the room. The circuit may then be reset by turning the toggle switch to the off position and immediately turning the switch to "on". This will start a new cycle in the timer circuit, completing the AC circuit for the time preset in the timing circuit. In lieu of flashing the lights, the timer may be equipped with an audible alarm.

The timing circuit, actuated by the load sensing circuit, is an integrated circuit having a built-in oscillator and multi-stage binary counter. The oscillator frequency is controlled by an RC circuit, enabling a simple potentiometer to be used for setting the time the circuit is to remain actuated.

Upon completion of the preset time interval, a signal is provided to turn the triac off, opening the circuit. The optional flashing warning may be provided by a bi-stable circuit actuated by the output signal from the timer upon completion of the present time interval. A bi-stable circuit flashes the power circuit on and off with a period determined by an RC circuit. The total time the flashing continues is also determined by an RC circuit.

Description of the Drawings Fig. 1 is a block diagram illustrating the functional purpose of certain groups of components of the invention; Fig. 2 is a circuit diagram illustrating individual components of the invention; Fig. 3 is a perspective view of a shallow, boxlike switch plate sized to accommodate the components illustrated in Fig. 2; Fig. 4 is a rear, elevational view of the switch plate of Fig. 3; Fig. 5 is an elevational view of a printed circuit assembly sized to fit within the switch plate of Fig. 3.

Detailed Description The instant invention is illustrated in a block diagram (Fig. 1 ) which sets forth the function of various groups of components.

Closing of the toggle switch connects a load, e.g., a room lamp, with an AC power source. (The toggle switch, load and power source are not part of the timing device.) A load sensor, detecting the presence of a current, energizes the DC Power Supply. Switch nos. 1 and 2 are open until the threshold voltage of the Power Supply is reached, which causes an enable relay to activate the timer.

Switch nos. 1 and 2 are closed by the timer. At the expiration of a predetermined time period, switch no. 2 is opened. The opening of switch no. 2 deactivates the trigger diode, which in turn fails to reclose switch no. 1 which opens momentarily each one-half cycle as the voltage curve passes through zero. As long as switch no. 2 is closed, the trigger diode immediately recloses switch no. 1 when it opens as the voltage curve passes through zero. When electronic switch no. 1 remains open, the flow of current to the load is terminated.

Referring now to Fig. 2, the present invention is connected to an existing AC power line comprising a power source 11, a load 12 and an "on-off" switch 1 3. The electronic assembly of the present invention is connected to the existing power source through connectors 14 and 1 5. A normally open triac 1 6 is connected in series with the power source 11, switch 13 and load 12 through connectors 14 and 1 5. One end of the triac is connected to the grounded end of the power line. (The ground is not an external ground, but is an internal common reference connection.) The other side is connected to a voltage sensing circuit comprising a diode 17, resistors 21 and 21 a, diode 22, zener diode 23, resistor 24, NPN transistor 25, and a resistor 26 and capacitor 27 connected in parallel to the collector 31 of transistor 25.The emitter 32 of transistor 25 is connected to ground. A single, smaller resistor could be substituted for resistors 21 and 21a.

When switch 13 is closed, line voltage appears across triac 1 6. The AC line voltage is rectified by a diode 1 7 and is passed to a power supply through diode 22 to terminal Va. The positive half waves from the terminal Va are applied to the anode 33 of diode 34 and across capacitor 35.

The positive going half waves are passed through diode 34 and applied across capacitor 36, charging cacacitors 35 and 36. Operating voltage is taken from terminal Vb connected to capacitor 36 and applied to terminal Vb connected to collector 31 of transistor 25 through an RC circuit comprising resistor 26 and capacitor 27.

The positive half wave pulses going to capacitor 35 continue to charge capacitor 35 until the voltage threshold is reached on zener diode 23. Zener diode 23 conducts once its threshold is reached and turns on transistor 25 charging capacitor 27 and providing a low going signal to timing circuit 37. Timing circuit 37 is a commercially available integrated circuit of the complementary analysis type. Timer 37 includes a sixteen stage binary counter, an integrated oscillator for use with an external capacitor and two resistors, and an automatic power reset circuit. A positive DC voltage is applied to terminal Vb from diode 34 and capacitor 36. The frequency of the oscillator circuit is controlled by resistor 41, capacitor 42, and variable resistor 43 in series with fixed resistor 43a which enables variation of the frequency of the oscillator, thereby changing the time interval.The output signal from transistor 25 is applied to terminal 44 and terminal 45 of timing circuit 37. The signal from transistor 25 resets the timer and initiates the oscillator and counter. The oscillator oscillates with a frequency determined by resistors 41 and 43 and capacitor 42. The sixteen stage counter divides the oscillator frequency.

When the counter is activated by the negative going pulse applied to terminal 44, the output signal foom timer 37 at terminal 46 is low. This low signal is applied to the base electrode 47 of NPN transistor 51. Resistor 48 is an emitter resistor for emitter 52 and acts as a current limiter for LED 53. Resistor 49 is a pullup for the base of transistor 51 to ensure that the transistor will go off when the timer output is high. Emitter 52 of transistor 51 is held at a positive voltage by the voltage appearing across capacitor 35. The transistor conducts, energizing light emitting diode 53. Light emitting diode 53 triggers a light sensitive disc 54, completing a circuit through zener diode 55 and resistor 56. Resistor 56a limits the amount of current exposed to disc 54.The AC voltage appearing across resistor 56 then triggers triac 16, completing the circuit through connectors 14 and 15, load 12, closed switch 1 3 and AC power source 11.

Upon completion of the time period set by variable resistor 43 and timing circuit 37, the output of timing circuit 37 goes high. The high signal is passed through resistor 57 to base electrode 47 of transistor 51. Transistor 51 is cut off, extinguishing light emitting diode 53. Disc 54 opens, stopping the trigger pulses to triac 1 6. As a result, triac 1 6 opens, opening the circuit and removing power source 11 from load 12.

An optional circuit (flash warning circuit) is included, enabling intermittent power application to load 1 2 for a period of time before power is cut off entirely. Resistor 57 is removed from terminal 62 and reconnected to terminal 63, connecting a gate circuit including gates 64, 65, 66 and 67.

Gate 66 must be a schmitt trigger AND gate in this configuration. Upon sensing the load and starting of the counter, the inputs to gate 64 are low, resulting in high output from gate 64. The output of gate 64 is connected through resistor 71 to an input of gate 67. As will be seen, both inputs to gate 67 are high, thereby providing a low output to base electrode 47 of transistor 51 causing said transistor to conduct. The upper input to gate 66 is low, since it is connected to the output from timing circuit 37. Output 46 is also connected to an input terminal of gate 65 through a resistor 77 and diode 81.

Simultaneously, a capacitor 76 is discharged. As long as output 46 is low, the output of gate 65 is high. Upon completion of the time period preset in timer 37, capacitor 76 charges through resistor 75. As long as the charge on capacitor 76 is less than the positive threshold of gate 65 the output of gate 65 remains high, and the output of gate 67 continues to energize transistor 51. After the charge on capacitor 76 has reached threshold, the output of gate 65 goes low, causing the input to gate 67 to go low and cutting off transistor 51.

However, during the time between the end of the time period, when the output of timer 37 goes low, and the discharge of capacitor 76, the output of gate 66 goes high and low intermittently as capacitor 74 is alternately charged and discharged through resistor 73 to the upper threshold of gate 66 and discharged through resistor 72 and diode 78 to the lower threshold of gate 66. This voltage, applied to one of the input of gate 67, causes the output of gate 67 to go alternately high and low, alternately cutting off and energizing current flow through transistor 51. It will be seen, therefore, that triac 1 6 will alternately be triggered on and off at a period determined by the RC circuit including capacitor 74 for the period of time determined by the discharge of the RC circuit comprising capacitor 76 and resistor 75.Diode 83 acts as resistor-diode and gate when output from gate 65 is high.

In the illustration of the circuitry in Fig. 2, the ground symbol has been used to indicate a common reference internal only to the device. It does not indicate an external ground of neutral wire of a power transmission line.

A wall plate 300 (switch plate) especially constructed for the purposes of this invention is illustrated in a perspective view in Fig. 3. An area about eight square inches is provided for the timer assembly components. The cavity formed is about one-half inch deep, providing a volume of about four square inches.

The face 301 of plate 300 is essentially flat except for the concave area, recessed zone 307, about the switch lever opening 302. The interior of the plate is essentially a cavity 309 formed by face 301 and sidewalls 303, 304, 305 and 306, not shown. Sidewalls 305 and 306 are the opposite walls from sidewalls 303, 304, respectively.

The rear edge of sidewalls 303, 304, 305, and 306 butt directly against the wall of a room containing a toggle switch. The peripheral dimensions of switch plate 300 are substantially the same as a conventional switch plate.

A peripheral cavity 309 around switch lever opening 302 is preferred so that space is permitted for the easy operation of the toggle switch without requiring remounting of the toggle switch. The recessed zone 307 permits easy fingertip access and operation of a switch lever protruding through opening 302.

The reverse side of plate 300 is illustrated in an elevational view in Fig, 4. The thickness of peripheral edge 308 of sidewalls 303,304,305 and 306 is preferably about one-sixteenth inch although varying wall thicknesses can be used depending upon the material of construction. A thermosetting rigid, insulating plastic is generally preferred, e.g., Borg Warner Cyclolac, or similar resins. Switch opening border 302a is substantially planar with peripheral edge 308.

A support plate 309 holds an insulating sheet 310 in position over printed circuit board 311 which contains the timer assembly, further illustrated in Fig. 5.

Wires 312 and 313 are connected in series with an existing toggle switch. These wires connect into connectors 1 4 and 15, as illustrated in Fig. 2.

The structure illustrated in Fig. 3 may be incorporated in a large switch plate adapted to cover a linear grouping of a gang of switches.

Such a large plate may be composed of a plurality of shallow, box-like switch plates integrally joined together, e.g., by forming in a multi-cavity die or mold.

The printed circuit assembly with various major components identified is illustrated in Fig. 5. The peripheral dimensions of the board are sized so as to fit within the peripheral cavity of plate 300. The opening 314 at the center of the board is sufficiently large so as to register with the recessed area 307 and permit the recessed area, including switch opening 302, to protrude therethrough. A timer knob 305 is shown on the rear of the device which may be used for selecting a particular time interval during which a lamp is to be lighted.

The instant invention has a number of significant advantages. First, the timer assembly and special plate form a compact, integral unit which requires attachment of only two wires in order to install the device to an existing toggle switch. Second, the device utilizes the existing toggle switch and does not require its removal, replacement or remounting. Third, the device has an appearance very similar to a conventional wall plate so it retains the aesthetics of a household, room, office or the like. Fourth, the electronic component assembly is such that once a time interval is selected, only the toggle switch lever need be operated in order to operate the timer.

Although the invention has been described herein as a device for installation in series with an existing switch, it can also be placed in parallel with an existing switch or device whereby it can function as a turn-off delay. For example, in a parallel hook-up, the turning off the toggle switch would not cease current flow to the load until the instant device "opens" the circuit on a predetermined delay basis.

Claims (15)

1. An electronic device for automatically operating an electrical circuit having a power source, load and switch after a predetermined time interval after said switch has been normally closed, comprising: electrical load sensing means: timing means in circuit with said load sensing means; electronic switch means adapted to be placed in serial relation with a power source and load; and control means for controlling the state of said electronic switch means in response to said electrical load sensing means and said timing means.

2. In the electronic device of Claim 1, said electrical load sensing means including voltage sensing means providing an input signal to said timing means, said load sensing means being in circuit with said electronic switch means.

3. In the electronic device of Claim 2, said electronic switch means including: normally open triggerable switch means adapted to be placed in serial relationship with said load and power source; and coupling means responsive to said timing means to trigger said triggerable switch means to a circuit closing condition.

4. In the electronic device of Claim 3, said timing means including time varying means for selecting the time interval said electrical circuit is to remain closed.

5. In the electronic device of Claim 4, said triggerable switch means comprising a triac.

6. In the electronic device of Claim 5, flash warning means in circuit with said timing means, and means for selectively connecting said flash warning means in circuit with said optical coupling means.

7. In the electronic device of Claim 6, said flash warning means including: gate means in circuit with said timing means; a first resistor-capacitor circuit connected to said gate means adapted to alternately open and close said triggerable switch means; and a second resistor-capacitor circuit adapted to disable said first resistor-capacitor, opening said triggerable switch means.

8. In the electronic device of Claim 3, said coupling means comprising optical coupling means.

9. An electronic device for automatically opening an electrical circuit having a power source, load and a manual switch, a predetermined time interval after said switch has been manually closed, comprising: normally open triac electronic switch means adapted to be placed in serial relationship with said power source and load; optical coupling means adapted to close said triggera ble electronic switch means; timing means in circuit with said optical coupling means; a variable resistor and capacitor connected to said timing means for selecting a time interval; load sensing means connected to said triac electronic switch means and said timing means for initiating said timing means upon closure of said manual switch; circuit means connecting said timing means to said optical coupling means; gate means in circuit with said timing means;; a first resistor-capacitor circuit connected to said gate means adapted to alternately open and close said triac triggerable switch means; a second resistor-capacitor circuit adapted to disable said first resistor-capacitor circuit, enabling said gate means to open said triac triggerable switch means; and circuit means selectively connecting said optical coupler controlling said triac triggerable switch means to said timing means in one position and to said gate means in a second position.

1 0. A wall switch plate and electronic timer device for connection to an existing toggle switch comprising: a shallow box-like switch plate having a substantially flat front face with a central recessed area having a switch lever opening therein, said plate having narrow sidewalls within the rear edge of said sidewalls and the switch lever opening in substantially the same plane, and a rectangular circuit board assembly having a central opening therein in register with the central recessed area of said switch plate.

11. The wall switch plate of Claim 9 wherein the width and length of said plate are substantially the same as a conventional single toggle switch plate.

1 2. The wall switch of Claim 10 wherein the depth of said shallow box-like switch plate is less than about three-quarters (3/4) inch.

13. The wall switch plate of Claim 10 wherein said circuit board timer comprises an electrical circuit including load sensing means, a timing circuit and electrical switch means to open and close said load circuit controlled by said toggle switch in response to said load sensing circuit and said timing circuit.

14. The wall switch plate of Claim 10 wherein a plurality of shallow-box like switch plates are an integral part of a large switch plate adapted to cover a linear grouping of a gang of toggle switches.

15. An electronic device for automatically operating an electrical circuit having a power source, load and switch after a predetermined time interval after said switch has been normally closed, substantially as herein described with reference to Figures 1-5 of the accompanying drawings.