United States Patent 1191
`
`[11]
`
`Patent Number:
`
`4,649,323
`
`Date of Patent:
`Mar. 10, 1987 ’
`[45]
`Pearlman et a1.
`
`[54]
`
`[75]
`
`MICROCOMPUTER-CONTROLLED LIGHT
`SWITCH
`
`Inventors: Gordon W. Pearlman; Steven B.
`Carlson, both of Portland, Oreg.
`
`[73]
`
`Assignee:
`
`Lightolier Incorporated, Jersey City,
`NJ.
`
`[21]
`
`[22]
`
`I51]
`[57-]
`
`[58]
`
`[561
`
`Appl. No.: 724,015
`
`Filed:
`
`Apr. 17, 1985
`
`Int. Cl.4 ............................................. H053 37/02
`US. Cl. ................................... 315/307; 315/292;
`315/293; 315/362
`Field of Search ................ 315/307, 292, 293, 362
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6/1972 Isaac .................................... 315/292
`3,668,467
`3,706,914 12/1972 Van Buren
`315/316
`3,766,431 10/1973
`Isaacs ............
`315/292
`3,805,096 4/1974 Hamilton ..
`315/292
`3,968,401
`7/1976 Bryant .......
`315/293
`
`4,240,011 12/1980 Dinges ......
`315/292
`
`....... 315/294
`4,241,295 12/1980 Williams
`4,287,468
`9/1981 Sherman
`SIS/DIG. 4
`
`4,289,972 9/1981 Wern ................... 315/362
`4,359,670 11/1982 Hosaka et al.
`..................... 315/307
`
`
`
`Primary Examiner—Harold Dixon
`Attorney, Agent, or Firm—Chemoff, Vilhauer, McClung
`& Stenzel
`
`[57]
`
`ABSTRACT
`
`A light level controller includes a microcomputer con-
`trolled light switch which responds to a manual tap or
`a longer manual depression of the switch in order to
`initiate various control modes for a light source. Preset
`levels of light intensity may be stored in the microcom-
`puter’s memory and an automatic fade mode may be
`initiated to cause the level of light intensity to fade from
`a current level to a preset level at a pre-established rate.
`The controller may respond to the momentary depres-
`sion of the switch to initiate the automatic fade mode or
`
`if tapped while a fade is in progress it may cause the
`light source to make an abrupt transition to either full
`on or full off, depending on whether a higher or lower
`level of light intensity is desired. A depression of the
`switch for a period longer than a tap will cause the level
`of light intensity to continue to change until the switch
`is released, and simultaneously this level will be stored
`in memory.
`
`21 Claims, 8 Drawing Figures.
`
`12
`
`I8
`
`DC POWER
`
` AC MAINS
`IZOV 60
`
`CYCLE AC
`‘LY
`
`FlSTOR
`
`
`
`
`
`
`I.
`
`
`REMOTE
`INPUT
`
`
`l4
`
` RECTIFIER
`AND CLAMP
`
`(POSITIVE)
`MICRO
`
`COMPUTER
`
`
`RECTIFIER
`AND CLAMP
`(NEGATIVE)
`
`2
`
`1
`
`APPLE 1026
`
`1
`
`APPLE 1026
`
`

`

`US Patent Mar. 10,1987
`
`Sheet] of3
`
`4,649,323
`
`FIG.|
`IE
`[8
`AC MAWS
`DC POWER
`
`IZOV 60
`CYCLE AC
`
`
`
` ZEROCROS$NG
`
`DETECTOR
`
`l4
`
`126
`
`SUPPLY
`
`
`
`(NEGATIVEDI
`
`
`
`LED DBPLAY
`
`J1? 24°
`
`
`'
`
`.
`
`‘
`
`
`
`30"
`
`MICRO
`
`COMPUTER
`
`
`RECTIFIER
`AND CLAMP
`(Posnwven
`
`RECTIHER
`AND CLAMP
`
`FIGS '
`
`
`
`
`AC UNE
`[20 V "
`
`ZERO
`CROSS
`
`HRWG aGNAL
`FROM MmROCOMPUTER
`
`'
`
`_
`
`1
`
`,
`
`LOAD
`VOLTAGE
`
`70°
`
`2
`
`

`

`US Patent Mar. 10, 1987
`
`Sheet 2 of 3
`
`4,649,323
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`

`U.S. Patent Mar. 10,1987
`
`Sheet3 §f3
`
`4,649,323
`
`C= CURRENT LEVEL
`
`N= NEW LEVEL
`‘
`
`P= PRESET
`LEVEL
`
`
`‘
`F I G 4b
`C = CURRENT LEVEL
`N = NEW LEVEL
`P= PRESET
`LEVEL
`
`
`
`
`INCREMENT
`N=C
`
`
`P=C
`
`
`
`DECRCEMENT
`
`N=C
`P=C
`
`
`
`No
`
`DE LAY=
`DELAY + I
`
`
`
`FIG.4a
`C= CURRENT LEVEL
`N= NEW LEVEL
`P = PRESET
`LEVEL
`
`4
`
`

`

`1
`
`4,649,323
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`MICROCOMPUTER-CONTROLLED LIGHT
`SWITCH
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a manually operated
`switch such as a wall-mounted light switch for control-
`ling the level of light intensity from a light fixture and
`more particularly to a light level controller actuated by
`the switch which includes a microcomputer for initiat-
`ing control programs to regulate the level of light inten-
`sity.
`Wall-mounted light switches which include a dimmer
`have become increasingly popular especially for resi-
`dential applications where it is desired to precisely con-
`trol the level of light intensity in a particular room.
`Such light switches usually include a variable resistor
`which is manually manipulated to control the voltage
`input to the light, where the variable resistor is con-
`nected in series with the household AC power line. A
`desirable feature in such switches would be the ability
`to return to predetermined levels of light intensity from
`conditions of either full power on or full power off. At
`present, however, such switches have no such memory
`and formerly established light intensity levels may be
`reestablished only by manual Operation and guesswork.
`There are in existence, however, touch actuated dim-
`mer controls which cycle through a dim to a bright
`cycle and back again, and include a memory function
`such that removing the hand from the switch will stop
`the cycle and store the level of light intensity at that
`point in memory. A subsequent touch will turn the light
`off and yet a further touch will return the light to its
`previous intensity level based upon the value of the
`intensity level stored in memory. While an improve-
`ment over the manually-operated variable-resistor type
`of dimmer, this dimmer may require the user to manu-
`ally cycle through a complete cycle of dim light to
`bright light to arrive at a desired intensity level. This
`latter switch is known as a DECORA ® touch dimmer
`and is manufactured by Leviton Manufacturing Com-
`pany, Inc. of Littleneck, N.Y. The DECORA ® touch
`dimmer, however, lacks the versatility needed for cer-
`tain aesthetic effects such as an automatic gradual fade
`from one light level to another. Moreover, it cannot
`change the direction, that is, either the increasing (up)
`or the decreasing (down), of light intensity from one
`direction to another without completing a full cycle
`from dim to bright and back again. Also, the touch
`dimmer has no “remote” capability that would enable
`one to use its features from a remote location such as a
`hallway or another room. Full function remotes are
`common with ordinary two-position light switches, but
`have not been available for dimmers because of the
`complexity of the circuitry.
`Yet another touch-type light control is shown in
`Hamilton, U.S. Pat. No. 3,805,096, and in Hosaka, et al.,
`U.S. Pat. No. 4,359,670. These devices are responsive to
`the duration of touch for initiating various control func-
`tions but include no provision for automatically fading
`light from one level to another.
`Automatic fading has in the past been available only
`in theatrical lighting systems employing very compli-
`cated switching inputs such as keyboard commands or
`elaborate banks of switches. Examples of such systems
`are shown in Williams, U.S. Pat. No. 4,241,295; Dinges,
`et al., U.S. Pat. No. 4,240,011; Van Buren, U.S. Pat. No.
`
`5
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`10
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`15
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`25
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`55
`
`65
`
`2
`3,706,914; and Isaacs, U.S. Pat. Nos. 3,766,431 and
`3,668,467.
`SUMMARY OF THE INVENTION
`
`The present invention provides a highly versatile
`microcomputer-controlled light level intensity switch
`which is operated by a pair of non-latching switches
`which provide inputs to the microcomputer. The non-
`latching switches may be arranged as upper and lower
`switches on a rocker panel or independent pair of panels
`which are normally biased to remain in a neutral posi-
`tion. The switches are each connected in series with the
`AC mains power line so that when either switch is
`depressed a signal in the form of a series of sequential
`pulses is provided to the microcomputer.
`When the switch is depressed in either the up or
`down direction,
`the microcomputer first determines
`whether the depression of the switch is momentary, that
`is, a brief tap, or whether it is being held down for a
`period of more than transitory duration. When the
`switch is held, the microcomputer advances the level of
`light intensity in the direction indicated by the switch,
`that is, either towards bright or towards dim. When the
`switch is subsequently released the microcomputer
`stores that current level of light intensity as a “preset”
`level in its memory. If the switch is first tapped in either
`direction with the light intensity at some static level the
`microcomputer will cause the level of light intensity to
`automatically advance or “fade” towards a predeter-
`mined level, either “full on,” “off,” or “prese .” The
`fade may occur at a rate which can be programmed in
`the microcomputer. If desired, the speed of the fade
`may vary depending upon whether the fade is from dim
`to bright or vice versa. For example, it is possible to
`program all downward fades to occur more gradually
`than all upward fades. If the switch is tapped again
`while the light intensity is fading towards the preset
`level, the microcomputer will halt the fade and cause
`the light intensity level to abruptly shift to the preset
`level. If the “up” switch is tapped with light at the
`preset level, the light intensity will fade to full maxi-
`mum. If it is tapped in the downward position when the
`light intensity level is at the preset position the light
`intensity will fade towards zero. Thus, the microcom—
`puter interprets the character of the command, that is, a
`hold or a tap, determines the current control mode, and
`initiates a light intensity control function accordingly.
`The three types of programs are preset, automatic fade,
`and abrupt transition.
`The non-latching switches provide a pulse input,
`which is derived from the AC power source, to the
`light switch through a clamp and half-wave rectifying
`network. Thus, the input to the microcomputer is a
`series of square wave pulses. The microcomputer has an
`internal program which counts the number of a sequen-
`tial series of pulses to determine if the switch is being
`tapped or held and executes a control program mode
`accordingly.
`The microcomputer is connected to a source of light
`such as an incandescent light bulb of between 40 and
`2,000‘watts by means of a thyristor solid state switch.
`The thyristor controls power to the incandescent light
`source by turning on at a predetermined phase angle
`relative to the phase of the AC line source. For this
`purpose the thyristor is responsive to a timed firing
`signal generated by the microcomputer according to
`the program in Operation. The firing signal is synchro—
`nized with the incoming power supply line by a zero
`
`5
`
`

`

`3
`crossing detector which detects the transition in the AC
`power line from positive to negative. The microcom-
`puter receives the zero crossing information and syn—
`chronizes this information with its internal clock which
`controls the timing of the firing signal for the thyristor.
`In this way the timing of the thyristor firing signal is
`calibrated to the desired level of light intensity and
`represents a phase angle at which the AC line is gated
`into the incandescent light source.
`When either the “up” or “down” switch is held the
`computer first determines the current level of light
`intensity. The microcomputer then causes the level of
`light intensity to increase for “up” or decrease for
`“down” in predetermined increments by initiating thy-
`ristor firing signals which either advance the phase
`gating of the AC wave or retard it. As long as either
`switch is held “on,” the level of light intensity will
`gradually advance or decline. Each time an additional
`increment of light intensity is added it replaces the cur-
`rent level in the memory which continues to be sampled
`in a closed-loop fashion until the switch is released.
`When the switch is released the current level of light
`intensity is stored in memory as a “prese ” level.
`When either switch is tapped the microcomputer
`interrogates memory to find out if the current level is
`equal to the preset level. This determines whether a
`fade is in progress or whether the light intensity is not
`changing. The subsequent control modes, “fade” and
`“abrupt transition,” then depend upon whether the new
`level
`in memory is preset, full on, or full off, and
`whether the current level is higher than, lower than, or
`equal to this level.
`The switches are wired in line with the main lZO—volt
`AC line. Since the switches are at all times either “on”
`or “off” and there are no variable resistors used for the
`dimming function, a parallel set of remote switches, also
`wired in line with the AC line, may be provided to give
`full remote capability. Thus, another switch box may be
`provided in a hallway or adjacent room which fully
`duplicates the functions of the primary switch box with—
`out the necessity for duplication of the microcomputer
`and its associated circuitry. The remote switches are
`wired in parallel with the primary switches through
`their wall-mounted switch box forming a second paral=
`lel input to the microcomputer.
`A primary object of this invention is to provide a
`light level controller which provides a maximum de-
`gree of flexibility in altering levels of light intensity
`according to the desires of the user.
`A further object of this invention is to provide a light
`level controller which includes an automatic fader for
`gradually fading the light intensity level from a current
`level to a preset level.
`Yet a further object of this invention is to provide a
`light level controller having means for manually over-
`riding the automatic fader and for making abrupt transi-
`tions in light level intensity from a current level to a
`predetermined level.
`A still further object of this invention is to provide a
`light level controller having the above features which
`can be mounted within a standard wall switch panel box
`and connected to a standard 60-cycle AC household
`power supply.
`Yet a further of this invention is to provide a light
`level controller in a wall switch mounting which is
`microcomputer-controlled and responsive to the state
`of non-latching switches which provide a digital input
`signal to the microcomputer.
`
`10
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`4,649,323
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`4
`A still further object of this invention is to provide a
`light level controller having a plurality of light control
`modes in which the particular mode chosen is a function
`of the period of time that the non-latching control
`switch is pressed.
`A further object of this invention is to provide alight
`level controller in a wall switch mounting having a
`visual indication of the intensity of the light on the
`room.
`A still further object of this invention is to provide a
`wall-mounted light level controller having full remote
`capability.
`The foregoing and other objectives, features and
`advantages of the present invention will be more readily
`understood upon consideraton of the following detailed
`description of the invention taken in conjunction with
`the accompanying drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic block diagram of a circuit con-
`structed according to the present invention.
`FIG. 2 is a side view of a wall switch mounting con-
`taining the circuit of the present invention illustrated in
`FIG. 1.
`FIG. 3 is a front View of an alternate type of wall
`switch mounting.
`FIG. 3(a) is a side view of the wall switch mounting
`of FIG. 3.
`FIG. 4 is a flow chart diagram depicting the method
`of operation of the circuit illustrated in FIG. 1.
`FIG. 4(a) is a continuation of a portion of the flow
`chart diagram of FIG. 4.
`FIG. 4(b) is a further continuation of the flow chart
`diagram of FIG. 4.
`FIG. 5 is a waveform diagram illustrating the method
`of controlling the line voltage input to a light source
`using the circuit of FIG. 1
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`A light source 10 which may be, for example, an
`incandescent
`light source drawing between 40 and
`2,000 watts of power, is connected to a source of AC
`power 12 through a thyristor 14. The AC source 12 is a
`standard household power supply, 60—cycle,
`lZO-volt
`AC. The thyristor 14 is a bi-directional SCR controller.
`The control line 11 for the thyristor 14 is connected to
`a microcomputer 16. The microcomputer 16 is powered
`by a DC power supply 18 and includes an input from a
`zero crossing detector 20 which is also connected to AC
`power source 12. A wall switch mounting 22 (enclosed
`within the dotted line in FIG. 1) may include a pair of
`nonlatching switches 24a and 24b and an LED display
`26. The LED display may be connected to the mi-
`crocomputer 16 by a bus 28 which may include any
`desired plurality of lines. In the example shown in FIG.
`1, line 28 is an eight line bus. Each of the nonlatching
`switches 24a and 24b includes a rectifier and clamp
`circuit 30a and 3017, respectively, which provide half-
`wave rectification and voltage clamping. The switches
`24a and 24b are connected to AC power source 12
`through a resistor 17 and diodes 13 and 15. The output
`of the rectifier and clamp circuits 30a and 30b are con-
`nected as inputs to microcomputer 16. Microcomputer
`16 also includes a clock which may, for example, be a
`crystal oscillator 32. The microcomputer 16 also in-
`cludes as an input, a reset network 34. A remote input
`19 may also be provided as a parallel input to circuts 300
`
`6
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`

`

`4,649,323
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`and 30b. Remote input 19 is in all respects identical to
`the network of switches 24a and 2411 including resistor
`17 connected to the AC line and diodes 13 and 15. Thus,
`either the wall mounting 22 or the remote input 19 may
`initiate the functions discussed herein.
`Between thyristor 14 and light source 10 there is a
`choke or induction coil 36 which provides current
`damping for the light source 10. Without such a choke
`36 the filament in an incandescent light source such as
`light source 10 may physically oscillate under certain
`conditions. Thyristor 14 has an output comprising AC
`pulses having relatively fast rise times. The choke 36
`smooths the shape of these pulses so that there is no
`ringing or spurious oscillation within the light source
`10.
`'
`The input of the microcomputer 16 from the rectifier
`and clamp circuits 30a and 30b is responsive to a series
`of sequential square wave pulses. These pulses are de-
`veloped from the line inputs through either switch 240
`or 2417. For example, if switch 24a is depressed the line
`voltage is fed to rectifier and clamp circuit 30a which
`provides half-wave rectification and clamps the voltage
`peaks to a level compatible with the microcomputer
`inputs, that is approximately 5 volts. The switches 24a
`and 24b are arranged to provide “up” and “down” light
`level changes, respectively. A detailed functional de-
`scription of the consequence of pressing either switch
`will be explained below, but, in general, switch 24a
`increases the brightness level of the light source 10 and
`may therefore be considered an “up” switch and switch
`24b decreases the brightness level of the light source 10
`and may therefore be considered a “down” switch.
`Accordingly, rectifier and clamp circuit 30b provides
`negative-going square wave pulses as an input to mi-
`crocomputer 16 and the circuit 300 provides positive-
`going square wave pulses. The reset network 34 pro-
`vides a signal that resets the microcomputer 16 upon
`initial power up of the system irrespective of fluctuation
`in the DC power supply 18. Such circuits are well
`known in the electronics art. The zero crossing detector
`20 determines the zero crossing points of the input
`power AC waveform from AC power source 12. This
`information is synchronized with the crystal oscillator
`32 so that the thyristor 14 may be controlled by gating
`voltage from the AC power source 12 into the light
`source 10 at predetermined times relative to the zero
`crossing points.
`Microcomputer 16 is a single chip microcontroller
`which may include read only memory and random
`access memory. Such a microcontroller is manufac-
`tured by National Semiconductor Co. and bears the
`model number COP4l3L. The microcomputer 16 re-
`ceives commands from the rectifier and clamp circuits
`30a and 30b, and synchronizes those commands with
`the zero crossing points of the AC power line by way of 55
`a signal from zero crossing detector 20, and provides
`appropriate firing commands to thyristor 14 over line
`11. The programs executed by microcomputer 16 and
`the method of operating switches 24: and 24b to
`achieve the programmed results will be explained be-
`low.
`Referring now to the flow chart diagrams of FIGS. 4,
`4(a) and 4(1)), there are four possible switch conditions
`for switches 24a and 24b. These are identified as the
`decision nodes “up held”, “down held”, “up valid”, and
`“down valid”. There also exists the possibility that none
`of the four above conditions exists and the light will
`remain at its current level by the continuous completing
`
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`of the zero crossing (“Z.C.”) subroutine, shown in the
`bottom half of FIG. 4, once every 1/ 120 second. This
`subroutine is responsible for generating a firing or com-
`mand signal over line 11 which controls the phase angle
`at which the triac fires during each é cycle of the 60
`cycle AC power input. If desired, the Z.C. subroutine
`may be executed every other half cycle or every third
`half cycle. Thus an instruction could be provided in the
`program to skip a certain number of half cycles before
`executing the Z.C. subroutine. The effect of such a
`instruction would be to provide a more gradual auto-
`matic fade or preset.
`The first step in the zero crossing subroutine is to
`determine if the current intensity level “C” equals a new
`or desired intensity level. The new level, indicated by
`the letter “N,” may have one of three values. It may be
`equal to the “preset" level “full on” or “full off.” Thus,
`in a case where N is equal to C, which would be the case
`if none of the switch conditions identified in the four
`decision nodes above currently existed, the microcom-
`puter 16 would determine the time of zero crossing of
`the AC input wave with reference to its own internal
`clock. As soon as it is determined that a zero crossing
`has occurred the microcomputer 16 begins counting
`until it reaches a point in time in the current half-cycle
`of the AC wave at which the voltage input will cause
`the light 10 to have the desired level of light intensity N
`(FIG. 5). This point in time may be expressed as a phase
`angle of the line input wave. At the predetermined
`phase angle the microcomputer will initiate a firing
`signal which will cause the thyristor 14 to gate the
`remaining portion of the AC voltage wave into the light
`source 10. The resultant voltage input which is shown
`as the “load voltage” line in FIG. 5 is a sharply rising
`pulse whose power content represents a fraction of the
`total available AC power line output. The sharply rising
`input wave form is smoothed by choke 36 to eliminate
`ringing or oscillation of the filament in the light source
`10.
`The thyristor 14 is fired once each half cycle and after
`each firing the microcomputer 16 interrogates the in-
`puts from circuits 30a and 30b to determine the status of
`switches 24a and 24b. The interrogation sequence and
`the resulting computations to determine the proper light
`level occur during a brief period of time at the begin-
`ning and at the end of each half cycle of the input wave-
`form as indicated by the shaded portions under the
`curve of the input wave in FIG. 5. During these periods
`no firing signal is generated and the thyristor 14 remains
`off. These are the points in the cycle, however, when
`the input voltage is lowest and the effect upon power
`availability is therefore negligible.
`The microcomputer 16 determines the status of the
`switches 24a and 2411 based upon the number of sequen-
`tial square wave pulses counted at each of the switch
`inputs from circuits 30a and 30b during each sampling
`period. Depressing either of the switches 24a or 2417 will
`cause circuit 30a or 30b to generate a series of square
`wave pulses for as long as the switch is depressed. Thus,
`the number of sequential pulses received is a function of
`the length of time that the user manually depresses the
`panel (refer to FIGS. 2 and 3) that actuates the switches
`24a and 24b. The microcomputer 16 counts the number
`of pulses in order to discriminate between a “hold"
`condition and a “tap” condition. If the microcomputer
`16 reads a predetermined number of pulses “u” when it
`interrogates a switch input it may interpret the condi-
`tion as a hold, and if it receives a number of pulses
`
`7
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`

`7
`greater than a predetermined minimum “m" but less
`than n it may interpret the switch condition as a “tap.”
`The predetermined minimum is necessary so that the
`micro-computer will not interpret spurious noise as a
`valid switch condition.
`Referring again to the top of FIG. 4, if n pulses are
`counted while the input from rectifying and clamp cir-
`cuit 300 is being sampled the microcomputer 16 deter—
`mines that the up switch is being held. It then deter-
`mines whether the current level of light C is at full
`power or less than full power. If the current level of
`light C is less than full the microcomputer increments C
`and simultaneously makes the new level just achieved
`equal to C and the preset level P equal to C. The zero
`crossing subroutine is then executed. The result of this
`loop is that as long as the user continues to depress
`switch 24a. the microcomputer 16 will cause C to incre-
`ment one step at a time per half cycle until the switch is
`released.
`If switch 24b remains depressed the mi-
`crocomputer 16 will decrement C simultaneously mak-
`ing N equal to C and P equal to C until the light is either
`fully off or until the user releases the button controlling
`switch 24b. The operations N=C and P=C are also
`memory operations and values of N and P are stored in
`memory for subsequent operations. The above de-'
`scribed loops represent the preset mode of light control
`and serve to establish a new value in memory for a level
`of light intensity P at the same time that a new level of
`light intensity is being established in the light source 10
`through the zero crossing subroutine.
`If during a sampling period the microcomputer 16
`discovers a “tap” condition on the “up” switch 24a. it
`executes the computational routine shown in FIG. 4(a).
`First the microcomputer 16 determines if the current
`level of light intensity equals the new or desired level of
`light intensity N. N could be the preset level stored in
`memory or could be a level corresponding to full power
`on. If C=N, the microcomputer 16 then determines
`whether C=full power. If yes, the zero crossing sub-
`, routine is executed. If no, microcomputer 16 determines
`, if N is then equal to P. If yes, the microcomputer makes
`. N equal to full power and executes the zero crossing
`subroutine. If no, the microcomputer 16 makes N equal
`to P and executes the zero crossing subroutine. When
`N=P or N=full and the zero crossing subroutine is
`executed, N will not be equal to C and therefore the
`command “move C one towards N” in the zero crossing
`subroutine will be executed. Since the computational
`routine in FIG. 4(a) established N as a value which was
`not equal to the current value C of the light intensity
`level, the zero crossing subroutine will repeat itself until
`N=C (assuming no switches have been depressed in the
`meantime), at which time the level of light intensity will
`remain constant at the new level N. Thus, when N does
`not equal C in the zero crossing subroutine, an auto-
`matic fade mode is initiated which moves C one incre-
`mental value towards N each time the loop is repeated.
`This loop is executed a chosen number of times a second
`and by choosing that number or the magnitude of the
`incremental steps through which N moves, the designer
`may regulate the slope of the automatic fade mode. For
`example, if the increments of N are made very small it
`would take the completion of more loops to move C to
`the value of N (a slower fade) than it would if the incre-
`mental values of C were made larger (a faster fade).
`According to the preferred embodiment, each half
`cycle is divided into 160 incremental steps and the Z.C.
`subroutine is executed every third half cycle. This re-
`
`10
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`15
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`20
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`25
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`30
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`35
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`45
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`50
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`55
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`65
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`4,649,323
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`8
`sults in a fade in which the incremental increases or
`decreases in light intensity are imperceptible and the
`fade appears to be smooth and continuous.
`If the up button is tapped while the automatic fade
`mode is in operation, a different set of conditions will
`exist at the first decision node in FIG. 4(a). In this case
`C will not be equal to N because N=P¢C and the
`microcomputer 16 will be in the process of fading C
`towards N. In such a case the microcomputer first de-
`termines if N is greater than or less than C. If N is
`greater than C, C is assigned a value that is equal to N.
`This causes the level of light intensity to abruptly jump
`from C to N. When the zero crossing subroutine is
`executed N will then be equal to C and the automatic
`fade mode will be circumvented as shown in FIG. 4.
`Thus, the difference between a fade and an abrupt tran-
`sition lies in making C either equal to a new or desired
`level N or in making C equal to some value that is not
`N prior to execution of the zero crossing subroutine.
`For example, if N is not greater than C in FIG. 4(a),
`microcomputer 16 makes N equal to P, a preset level
`which is lower than C. Since N is then not equal to C at
`the commencement of the zero crossing subroutine, C
`moves one step at a time towards N which is lower than
`C, and a downward automatic fade is commenced.
`The operation of the switch when the down button is
`tapped is similar in operation to the situation encoun-
`tered when the up button is tapped. If no fade is in
`progress when the down button is tapped, C will be
`equal to N. Subsequently, N will be made equal to zero
`and the zero crossing subroutine will cause the light
`intensity level to fade to off. If a fade is in progress such
`that when the down button is tapped, N is either equal
`to, greater than, or less than C, the light either fades to
`off or makes an abrupt transition to off. A delay mode
`may be provided when a down fade is in progress to
`make downward fading more gradual
`than upward
`fading. Thus, if during a Z.C. subroutine a downward
`fade is detected, the microcomputer 16 delays the thy-
`ristor firing until the delay subroutine has been com-
`pleted, incrementing the delayinnction one step at a
`time until its completion. If the down button is pressed
`while an up fade is in progress, N is made equal to zero
`and C fades toward N in the zero crossing subroutine. If
`the down is pushed while the system is fading towards
`off, N will be less than C and microcomputer 16 will
`make C equal to N which will cause the auto-fade mode
`in the zero crossing subroutine to be circumvented and
`the light will make an abrupt transition to off.
`Physically the system represented in the block dia-
`gram of FIG. 1 may be enclosed in a wall mounted light
`switch. One example of such a switch is shown in the
`side view of the switch in FIG. 2. The switch of FIG. 2
`includes a cover plate 38 and a rectangular bezel 40.
`The bezel 40 encloses a rocker mounted panel 42 which
`includes two inwardly extending fingers 44a and 44b.
`The fingers 44a and 44b are adapted to make contact
`with non-latching push buttons 46a and 46b. The push
`buttons 46a and 46b are mounted on a PC board 48
`which also includes the circuit elements shown in the
`block diagram of FIG. 1 with the exception of the in-
`candescent light source 10 and the AC power supply 12.
`The PC board 48 is mounted to an aluminum heat sink
`50. An air gap safety switch 52 is also mounted to the
`heat sink which breaks the circuit when slider 67 is
`actuated. The switch components are enclosed in a box
`54 of a size compatible with the current size standards
`for wall-mounted light switch boxes. Inside the box 54
`
`8
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`

`

`9
`is choke coil 36. An aperture 56 in box 54 provides a
`means for connection to the incandescent light source
`10 by way of wire 58. The rocker panel 42 includes
`apertures 60 (only one such aperture is shown in FIG. 2)
`in which are mounted light-emitting diodes (LEDs)
`such as LED 62. LED 62 is part of LED display 26
`identified in FIG. 1. There may be as many LEDs as
`desired. According to the preferred embodiment there
`should be eight because the National Semiconductor
`chip used for microcomputer 16 has eight outputs
`which may be arranged to provide a signal indicating
`the current level of light intensity. For example, the
`LEDs may be arranged in an array extending along the
`rocker panel 42 from top to bottom so that the vertical
`position in the array of the LED that is on indicates the
`level of brightness. The nonlatching push buttons 46a
`and 46b correspond functionally to switches 24a and
`24b in FIG. 1. Thus, depressing the upper portion of the
`rocker panel 42 will cause finger 44a to engage push
`button 46a and close the “up” switch 240. Similarly,
`pressing the lower half of rocker panel 42 will close
`“down” switch 24b. The rocker panel 42 is biased by a
`pair of an