United States Patent
`[19]
`[11] Patent Number:
`5,994,844
`
`Crawford et al.
`[45] Date of Patent:
`Nov. 30, 1999
`
`1J5005994844/\
`
`[54] VIDEO LIGHTHEAD WITH DIMMER
`CONTROL AND STABILIZED INTENSITY
`
`[75]
`
`Inventors: James J. Crawford; Kevin J.
`-
`cranord’ bOth 0f ngWOOd’ N‘J’
`
`[73] Assignee: Frezzolini ELectronics, Inc.,
`Hawthorne, N-J-
`
`[21] Appl. No.: 08/989,923
`22
`F1 d:
`D . 12 1997
`[
`]
`1 e
`ec
`’
`[51]
`Int. Cl.6 ............................... G03B 15/02; G01] 1/32
`[52] US. Cl.
`.......................... 315/151; 315/158; 315/224;
`362/4
`[58] Field of Search ..................................... 315/149, 151,
`315/150, 152, 155, 158, 297, 153, 307,
`362, DIG. 4, 208, 224; 362/4, 5, 18, 276
`
`[56]
`
`References Cited
`
`3,967,106
`4,192,584
`4,300,075
`
`U'S' PATENT DOCUMENTS
`6/1976 Chen ........................................... 362/4
`3/1980 Dougherty
`...... 353/30
`
`............................ 315/307
`11/1981 Foose et a1.
`
`4,368,406
`......................... 315/158
`1/1983 Kruzich et a1.
`4,749,913
`..... 315/175
`6/1988 Stuermer et a1.
`
`4,959,755
`9/1990 Hochstein ............... 315/151
`32112313: 131335 {#Yhacoftl‘fl
`~~~~~ 333/3353
`,
`,
`1 son e a .
`............................
`5,747,938
`5/1998 Beard ...................................... 315/155
`
`Primary Examiner—Don Wong
`Assistant Examiner—Wilson Lee
`Attorney, Agent, or Firm—Darby & Darby
`[57]
`ABSTRACT
`Avideo lighthead mountable to a video camera and having
`a dimmer control that varies the intensity of the light output
`from the lighthead using pulse Width modulation techniques.
`Aphoto sensor measures the intensity of light reflected from
`a subject in from of the lighthead The intensity of light
`output from the lighthead is adjusted by control circuitry in
`response to changes in measured reflected light intensity to
`maintain a constant level of illumination. The adjustment is
`carried out by modifying the duty cycle of a pulse Width
`modulation circuit. The duty cycle adjustment of the pulse
`Width modulation is also used to compensate for supply
`Voltage Variations in order to maintain constant light output
`
`7 Claims, 8 Drawing Sheets
`
`
`
`LIGHT
`
`
`+VO-
`
`
`
`MICRO-CONTROLLER
`
`A/D
`INPUT VOLTAGE
`
`SENSOR
`' ROTARY
`
`' ENCODER
`INPUT
`
`‘
`B
`
`‘
`
`47
`
`3
`
`7
`
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`
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`
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`
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`
`HTC, Exhibit 1013
`
` REFLECTED
`
`
`
`AUTO/SET
`
`_
`
`
`
`PUSH
`
`A/D
`CONVERTER
`
`PWM
`CIRCUIT
`
`ON/OFF
`
`
`
`PRESETI
`PRESETZ
`27a 23
`
`
`~ ESLTngL
`INPUT
`39
`
`
`
`
`REMOTE
`INPUT
`
`CABLE, RF
`
`0R IR LINE
`
`
`HTC, Exhibit 1013
`
`

`

`US. Patent
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`HTC, Exhibit 1013
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`US. Patent
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`
`HTC, Exhibit 1013
`
`
`
`

`

`US. Patent
`
`Nov. 30, 1999
`
`Sheet 3 0f 8
`
`5,994,844
`
`FIG. 5
`
`100
`
`
`
`
`
`
`
`
`GOTO
`
`HMER
`
`SUBROUHNE
`
`101
`
` GOTO
`PUSH BUTTONS
`SUBROUHNE
`
`
`SUBROUHNE
`
`GOTO
`
`SUBROUHNE
`
`102
`
`104
`
`106
`
`
`
` GOTO
`ROTARY ENCODER
`
`
`
`BATTERY CHECK
`
`
` GOTO
`
`PHOTO—CELL
`
`
`
`
`SUBROUHNE
`
`
`108
`
` GOTO
`LAMP CONTROL
`
`SUBROUHNE
`
`110
`
`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`

`

`US. Patent
`
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`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`
`
`
`
`

`

`US. Patent
`
`Nov. 30, 1999
`
`Sheets 0f8
`
`5,994,844
`
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`HTC, Exhibit 1013
`
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`
`

`

`US. Patent
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`
`HTC, Exhibit 1013
`
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`
`
`

`

`US. Patent
`
`N0V.30, 1999
`
`Sheet 7 0f 8
`
`5,994,844
`
`FIG- 9
`
`186
`
`NO
`
`RETURN
`
`184
`
`
`
` IS
`AUTO_MODE
`
`SET?
`
`
`YES
`
`188
`
`
`
`
`CURRENT
`
`
`
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`YES
`READING > PHOTO
`
`CELL RAM?
`
`
`
`
`CURRENT
`
`PHOTO CELL
`
`NO
`
`194
`
`
`READING < PHOTO
`
`YES
`
`CELL RAM?
`
`
`
`NO
`
`RETURN
`
`200
`
`190
`
`DECREASE
`PWM UNTIL
`
`MINIMUM
`
`RETURN
`
`196
`
`INCREASE
`PWM UNTIL
`
`MAXIMUM
`
`RETURN
`
`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`

`

`US. Patent
`
`N0V.30, 1999
`
`Sheet 8 0f8
`
`5,994,844
`
`LAMP
`
`CONTROL
`
`202
`
`FIG.
`
`IO
`
`IS
`
` NO
`
`
`
`
`
`
`TURN OFF
`LAMP
`
`(CLEAR PWM)
`
`
` IS
`
`BATTERY LOW
`
`LAMP STATUS
`
`ON?
`
`210
`
`
`
`208
`
`RETURN
`
`
`
`FLAG SET?
`
`NO
`
`TURN ON
`
`212
`
`LED INDICATOR
`
`
`
`
`TURN ON LAMP
`TRANSISTOR
`USING PWM
`
`214
`
`216
`
`RETURN
`
`FIG.
`
`||
`
`TIMER SUBROUTINE
`
`
`
`CHECK
`CURRENT
`CLOCK VALUE
`
`
`
`HAS
`
`
`1 MS ELAPSED?
`
`
`
`
`
`
`YES
`
`RESET
`CLOCK VALUE
`
`RETURN
`
`202
`
`220
`
`
`
`224
`
`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`

`

`5,994,844
`
`1
`VIDEO LIGHTHEAD WITH DIMMER
`CONTROL AND STABILIZED INTENSITY
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a portable video lighthead
`typically used on video cameras. These lightheads may be
`used, for example, to provide illumination for video cameras
`used under low light level conditions and light fill situations
`when overhead lighting or strong sunlight creates dark
`shadows on the subject.
`Portable video lightheads are exemplified by the Mini-Fill
`lighthead line of Frezzolini Electronics, Inc. of Hawthorne,
`N.J. They are extremely lightweight at about 12 ounces and
`have a compact size of 2 by 4.5 inches. They typically
`operate from any 12 to 14 or 30 volt battery, utilize high
`efficiency mirror lamps and operate in the range of 20—100
`watts. They mount on any video camera, such as those used
`by the broadcasting industry for televising events.
`When used indoors, the Mini-Fill lightheads may be too
`bright for some purposes. It is therefore desirable to modify
`the brightness of the Mini-Fill lightheads so that they may be
`used indoors and yet satisfy the requirements for
`less
`obtrusive lightheads.
`Further, it is also desirable to maintain the overall bright-
`ness selected by the user at a constant level, even as ambient
`lighting conditions change, as the lighthead battery voltage
`drops, and as the subject moves closer to or further from the
`light source.
`
`SUMMARY OF THE INVENTION
`
`These and other problems are solved by the present
`invention, which, in one embodiment, provides a lighthead
`mountable on a video camera. The intensity of the emitted
`light is varied using pulse width modulation techniques. A
`light sensor coupled to the lighthead detects the intensity of
`reflected light and stores this value in an electronic storage
`area. The detected light intensity of the reflected light is
`compared with a presently measured light intensity and the
`intensity of the light emitted by the lighthead is adjusted to
`maintain a constant illumination of a subject even as ambi-
`ent lighting conditions change. The intensity of the emitted
`light is also maintained as constant in response to dropping
`battery voltage over time. The detected light levels may also
`used to provide preset lighting levels which can be recalled
`at the push of a button.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a better understanding of the present invention, ref-
`erence is made to the following description and accompa-
`nying drawings, in which:
`FIG. 1 is a block diagram of a lighthead in accordance
`with the present invention;
`FIG. 2 is a front view of the lighthead of FIG. 1;
`FIG. 3 is a back view of the lighthead of FIG. 1;
`FIG. 4 is a schematic diagram of a lamp illumination
`circuit in accordance with the present invention;
`FIG. 5 is a flowchart of the main loop of a microcontroller
`program for a lighthead according to the present invention;
`FIG. 6 is a flowchart of a Push Button Subroutine of a
`
`microcontroller program for a lighthead according to the
`present invention;
`FIG. 7 is a flowchart of a Rotary Encoder Subroutine of
`a microcontroller program for a lighthead according to the
`present invention;
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`FIG. 8 is a flowchart of a Battery Check Subroutine of a
`microcontroller program for a lighthead according to the
`present invention;
`FIG. 9 is a flowchart of a Photo-Cell Subroutine of a
`
`microcontroller program for a lighthead according to the
`present invention;
`FIG. 10 is a flowchart of a Lamp Control Subroutine of a
`microcontroller program for a lighthead according to the
`present invention; and
`FIG. 11 is a flowchart of a Timer Subroutine of a
`
`microcontroller program for a lighthead according to the
`present invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`FIGS. 1—3 show a lighthead 2 of the present invention
`which may be mounted on a video camera (not shown). The
`lighthead 2 includes a housing 8, a light source or bulb 12,
`a concave reflector 14 for reflecting light shining from the
`bulb to the front of the lighthead, and a transparent or
`translucent lens 16 in front of the reflector and bulb.
`
`The lighthead 2 is powered from a power source 17 which
`may be a battery or an AC adapter.
`In the preferred
`embodiment, the voltage is continuously monitored and the
`lamp is disabled when the measured voltage falls below a
`preset level. This is discussed in more detail below.
`In accordance with the invention, the intensity of the light
`emitted by the lighthead 2 is controlled using pulse width
`modulation techniques. The modulation frequency should be
`higher than the audio frequency band, otherwise the pulse
`modulation of the components may create a perceivable hum
`or whistle. The maximum modulation frequency is limited
`by the response time of the lamp filament and the switching
`circuit connected to the lamp. The intensity of the light is
`varied by adjusting the duty cycle of the pulse width
`modulated power signal applied to the bulb 12. This can be
`accomplished using input from a dimmer control such as
`rotary encoder 21. However, other methods, such as a
`slidable switch or a pair of “up” and “down” switches may
`also be used.
`
`the lighthead functions,
`In the preferred embodiment,
`including sensing user inputs and modulating the duty cycle,
`are controlled by a microcontroller 19. However, analog
`and/or discrete circuit elements may also be used as will be
`apparent to those skilled in the art.
`The modulated duty cycle (and thus the lamp brightness)
`is represented as a numerical value stored in memory, such
`as RAM, which may be provided as part of the microcon-
`troller or as a separate RAM unit. Preferably, several RAM
`locations are provided in which duty cycle values are stored
`to allow for the selection of a number of preset
`light
`intensities. Alternatively, measured reflected light intensities
`may be stored to provide for selection of a number of preset
`lighting intensity levels based on the particular reflected
`light intensity. In the preferred embodiment, two such pre-
`sets are provided which can be set by user input and
`retrieved to set the duty cycle of the light as needed.
`The lighthead 2 includes a photo-sensor 20 which may be
`attached to housing 8 by a bracket 22. The photo-sensor 20
`measures the intensity of light reflected from a subject in
`front of the lighthead 2. When the lighthead 2 is properly
`mounted on a camera, the measured intensity indicates the
`intensity of light entering the camera lens. The measured
`light intensity can be stored in memory in response to user
`input.
`
`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`

`

`5,994,844
`
`3
`According to a preferred embodiment of the invention,
`the lighthead 2 operates in two primary modes
`—STANDARD and AUTO.
`In STANDARD mode,
`the
`lamp 12 is turned on by a power push button 24. The on
`condition is indicated by the activation of LED 42. The
`modulated duty cycle and therefore the light output intensity
`is controlled via the rotary encoder 21 connected to the
`micro-controller 19. To turn the lamp off, the power button
`24 is pressed a second time.
`the lamp intensity is
`When operated in AUTO mode,
`adjusted via the rotary encoder 21 to a desired level. When
`the desired level is obtained, the AUTO button 26 is pushed.
`In response, the micro-controller 19 samples the value of the
`reflected light as measured by photo-sensor 20 and stores the
`value in memory. From that point on, the micro-controller 19
`uses updated reflected light intensity data from the photo-
`sensor 20 to automatically maintain the reflected light inten-
`sity at the previously stored intensity level by either increas-
`ing or decreasing the duty cycle of the operation of lamp 12,
`thus increasing or decreasing the lamp output intensity. As
`the battery voltage drops over time, the microprocessor will
`also adjust the intensity of lamp 12 to maintain a constant
`light output level. The AUTO mode is disabled by pressing
`the AUTO button 26 a second time.
`The micro-controller 19 can also store and retrieve addi-
`
`tional preset light intensity levels. To define a preset level,
`the lamp intensity is adjusted to a desired level by the
`operator using the rotary encoder 21. When the desired level
`is obtained, the user indicates that the level should be stored
`in the micro-controller 19. In the preferred embodiment, this
`is accomplished by continuously pressing the desired PRE-
`SET button 27, 28, for more than 3 seconds. In response, the
`duty cycle control value will be stored in a memory location
`in the micro-controller 19. This value represents the portion
`or percentage of the currently modulated pulse which is
`active. Preferably, the stored duty cycle level is recalled by
`pressing the appropriate PRESET button 27, 28, thus adjust-
`ing the lamp to the preset intensity level.
`A remote input device 30 can also be provided to allow a
`user to control some or all of the lighthead 2 functions from
`a distance. The remote input device 30 is preferably con-
`nected to the microcontroller by a cable 32. However, the
`connection may also be by any of a number of other types
`of communication links, such as a conventional radio-
`frequency, infrared or optical link. Preferably, the remote
`input device 30 supports all functions of the lamphead 2.
`FIG. 4 is a schematic diagram of a lamp illumination
`circuit in accordance with the invention. In the preferred
`embodiment, the micro-controller 19 is a RISC processor
`such as a PIC16C72 chip manufactured by Microchip
`Technology, Inc. This processor advantageously includes its
`own internal RAM, an analog-to-digital converter 37, as
`well as a free-running 25 kHZ pulse width modulation circuit
`39. Preferably, the microprocessor is operated at an external
`clock speed of approximately 4 MHZ with an internal clock
`speed of approximately 1 MHZ. In alternate embodiments,
`any or all of these circuit elements may be separate from the
`micro-controller 19.
`
`The power for the micro-controller 19 is provided by a
`conventional 5-volt voltage regulator 44. The micro-
`controller 19 continuously monitors the supply voltage to
`the system from node 46 using analog to digital converter
`47, here located within microcontroller 19, and will auto-
`matically turn off all lamp functions when the supply voltage
`falls below a preset level to insure that a full lighting range
`is always available. Other voltage sensing techniques may
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`also be used, as will be apparent to those skilled in the art,
`and the result input to microcontroller 19. For example, a
`comparator may be used to determine whether the supply
`voltage (or a fraction thereof as determined by a voltage
`divider) is less than a preset reference voltage, such as the
`regulated voltage from voltage regulator 44. Alternatively,
`the supply voltage may be measured using a Zener diode
`with a breakdown voltage equal to the preset level.
`The Power, Preset, and Auto switches, 24, 26, 27, and 28
`are connected to inputs of the micro-controller 19. The
`rotary encoder 21 is connected to a rotary encoder input of
`the micro-controller 19. The microcontroller is preferably
`configured to indicate when the rotary encoder 21 is turned
`and in what direction. This may be done, e.g., by using a
`rotary encoder 21 that generates an asymmetric sequence of
`signals as it is rotated, and monitoring the input sequence
`pattern with the micro-controller. Other techniques known to
`those skilled in the art may also be used. The microcontroller
`19 receives similar inputs from the remote input device 30
`via link 32.
`
`The photo-sensor 20 is preferably a photo-resistor and is
`connected in series between the power supply and a pull-
`down resistor 34. In this configuration, the voltage at node
`38 of the photo-sensor 20 is proportional to the intensity of
`light striking the photo-sensor 20. Node 38 is connected to
`an analog-to-digital converter 37, here shown within micro-
`controller 19. The voltage at node 38 is converted into a
`digital value which indicates the intensity of light striking
`the photo-sensor 20.
`The duty cycle of the pulse width modulated power signal
`applied to lamp 12 is controlled by micro-controller 19.
`Lamp 12 is connected in series with power transistor 36
`which is switched on and off under the control of output
`signal 40 from the pulse width modulation circuit 39 (here
`shown within micro-controller 19) which drives the power
`transistor 36 in a conducting or a non-conducting state.
`Preferably, power transistor 36 is a power MOSFET with a
`low activation voltage.
`The lighthead 2 functionality is controlled by a program
`executed by micro-controller 19.
`In the preferred
`embodiment, the program is stored in a memory physically
`located within micro-controller 19, however external storage
`can also be provided. The operating program will be dis-
`cussed in detail below with reference to FIGS. 5—10.
`
`FIG. 5 is a flowchart of the Main Loop 100 of a micro-
`controller program for a lighthead according to the present
`invention. The Main Loop (step 100) controls the overall
`program flow between the various subroutines. The main
`loop consists of a series of GOTO commands (steps
`101—110) which initiate the Timer, Push Button, Rotary
`encoder, Battery Check, Photo-Cell, and Lamp Control
`subroutines respectively. After each subroutine has been
`processed, the program loops and repeats steps 101—110.
`Using the preferred microcontroller 19 operating at an
`internal clock speed of approximately 1 MHZ,
`the Main
`Loop is executed approximately once every millisecond.
`This timing is maintained by using a software delay routine,
`discussed below. Each subroutine in the Main Loop will now
`be discussed in turn.
`FIG. 11 is a flowchart of a Timer subroutine of a micro-
`
`controller program for a lighthead according to the present
`invention. The Timer subroutine is the starting point of the
`Main Loop program flow. Under normal circumstances, the
`remaining subroutines 102—110 will execute in less than one
`millisecond. However, the exact amount of time may vary.
`Thus, the Timer subroutine is used to time or pace the flow
`
`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`

`

`5,994,844
`
`5
`of the program and maintain an approximately one milli-
`second execution time for the Main Loop 100. Each time the
`Timer subroutine is accessed,
`it checks the value of a
`free-running clock (not shown) to determine how long the
`rest of the Main Loop 100 took to execute (step 220). A
`delay is then introduced by looping until the proper amount
`of time has elapsed (step 222). After the proper period of
`delay, the clock value is reset to zero (step 224) and the
`program returns to the main loop (step 226). Other methods
`of introducing a delay to maintain a set program pace known
`to those skilled in the art may also be used.
`FIG. 6 is a flowchart of a Push Button Subroutine of a
`
`microcontroller program for a lighthead according to the
`present invention. The subroutine is entered from block 112
`and each input switch is examined in turn. If the ON/OFF
`button 24 is pressed (step 114), the program toggles the
`LAMP STATUS flag from off to on or on to off (step 116)
`and then returns to the main loop (step 118). In the preferred
`embodiment, only one button should be pressed at a time.
`Thus, once a pressed button is detected and the appropriate
`action taken, there is no need to continue within the sub-
`routine and check other buttons.
`
`The program then polls the AUTO button 26 (step 120).
`If this button is pressed,
`the reflected light
`intensity as
`measured by the photo-sensor 20 is stored in a designated
`location in RAM (step 122). The AUTO MODE flag is then
`toggled between on and off (step 124) and the program
`returns to the main loop (step 126).
`Next, the program polls the first preset switch 27 (step
`128). If the switch has been pressed for more than three
`seconds (step 130), the duty cycle for the current pulse width
`modulated light intensity is stored in a designated RAM
`location (step 132) and the program returns to the main loop
`(step 134). If the switch has been released before three
`seconds have elapsed, a previously stored duty cycle is
`retrieved from memory and used to set the present duty
`cycle. (Step 136). The program then returns to the main loop
`(step 138). The second preset switch 28 is polled in a similar
`manner to set or retrieve a second preset intensity. (Steps
`140—146; 150—152). The program then returns to the main
`loop at step 148. The switches on a remote unit 30 can be
`polled in a similar manner, as will be apparent to those
`skilled in the art.
`
`FIG. 7 is a flowchart of a Rotary Encoder Subroutine of
`a microcontroller program for a lighthead according to the
`present invention, which is entered at block 154. If the user
`is turning the rotary encoder 21 in a clockwise direction
`(step 156), the stored duty cycle value is increased unless a
`maximum value has been reached (step 158). The program
`then returns to the main loop (step 160). In the preferred
`embodiment, the duty cycle can be increased to 100%, i.e.,
`the light is continuously on. If the user is turning the rotary
`encoder 21 in a counter-clockwise direction (step 162), the
`stored duty cycle value is decreased until a minimum value
`has been reached (step 162). In the preferred embodiment,
`the duty cycle can be decreased to a value of 10%. The
`subroutine then returns to the main loop (step 166). If the
`rotary encoder 21 is not being rotated, the subroutine returns
`to the main loop without adjusting the duty cycle. (Step
`170). The rotary encoder 21 may operate in either a step-
`wise or continuous manner.
`
`FIG. 8 is a flowchart of a Battery Check Subroutine of a
`microcontroller program for a lighthead according to the
`present invention. Because an adequate light intensity from
`lamp 12 can only be maintained if the supply voltage is
`sufficient, the microcontroller monitors the power voltage at
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`
`node 46 (discussed above) and compares it to a minimum
`battery voltage. Preferably,
`the minimum voltage for a
`12—14 volt battery is 10 volts. If the battery voltage is greater
`than the minimum voltage (step 174), the subroutine simply
`returns to the main loop. (Step 176). Otherwise, the BAT-
`TERY LOW flag is set (step 178) and the subroutine returns.
`(Step 180).
`FIG. 9 is a flowchart of a Photo-Cell Subroutine of a
`microcontroller program for a lighthead according to the
`present invention. When this subroutine is entered (step
`182), the AUTO MODE flag is checked (step 184). If the
`AUTO MODE flag is not set, the routine returns to the main
`loop (step 186). If the AUTO MODE flag is set, indicating
`that the unit is in AUTO mode, the presently reflected light
`intensity, as measured by the photo-sensor 20, is compared
`with the previously stored reflected light intensity. If the
`present light intensity is too bright (step :188) (i.e., the
`present light intensity is greater than the previously stored
`reflected light intensity), the duty cycle is decreased, unless
`a minimum value has been reached (step 190), and the
`subroutine returns to the main loop (step 192). If the present
`light intensity is too dim (step 194) (i.e., the present light
`intensity is less than the previously stored reflected light
`intensity), the duty cycle is increased, unless a maximum
`value has been reached (step 196), and the subroutine returns
`to the main loop (step 198). If the present light intensity is
`equal to the stored intensity, the subroutine returns to the
`main loop without changing the duty cycle. (Step 200).
`Preferably,
`the maximum duty cycle is 100% and the
`minimum duty cycle value is 50%. Although the minimum
`value may be less than 50%, this may result in a shift in the
`color of the light, leading to decreased quality video images.
`Accordingly, in an alternative embodiment, this value may
`be selected by the user.
`It should be noted that AUTO mode will compensate not
`only for changes in reflected light
`intensity caused by
`changes in ambient lighting conditions, but also for changes
`resulting from a dimming of the light emitted by lamp 12 as
`the battery voltage drops. Thus, a stable light intensity is
`maintained for as long as possible.
`FIG. 10 is a flowchart of a Lamp Control Subroutine of a
`microcontroller program for a lighthead according to the
`present
`invention. This subroutine initially checks the
`LAMP STATUS flag. (Step 204). If the LAMP STATUS flag
`is off (indicating that the user has pressed the power button
`to turn off the lamp), the lamp is turned off by setting the
`duty cycle to zero (step 206) and the subroutine returns to
`the main loop. (Step 208). Next, the BATTERY LOW flag
`is checked. (Step 210). If it has been set by the Battery
`Check subroutine, the battery cannot supply enough voltage
`to adequately power the light. Accordingly, the lamp 12 is
`turned off by setting the duty cycle to zero. Alternatively, the
`lamp 12 may be turned off by means of a separate switch
`connected in series to lamp 12 and toggled by an output of
`microcontroller 19 or a separate voltage comparison circuit
`(not shown).
`If the lamp is on and the BATTERY LOW flag is not set,
`a power indicator LED 42 is activated (step 212) and the
`duty cycle is set accordingly (step 214). In the preferred
`embodiment, the pulse width modulation is controlled by
`free-running circuitry within the micro-controller 19 that
`operates independently of the program flow. In an alternative
`embodiment,
`the light modulation may be controlled
`directly with an appropriate software routine. However, this
`will increase program complexity.
`While the foregoing description and drawings represent
`the preferred embodiments of the present invention, it will
`
`HTC, Exhibit 1013
`
`HTC, Exhibit 1013
`
`

`

`5,994,844
`
`7
`be understood that various changes and modifications may
`be made without departing from the spirit and scope of the
`present invention.
`We claim:
`
`1. A video lighthead comprising:
`a lighthead having a housing;
`a light source located in said housing;
`a pulse width modulation circuit for controlling said light
`source, wherein the brightness of said light is deter-
`mined by the duty cycle of said pulse width modulation
`circuit;
`a photo-sensor for measuring the intensity of light
`reflected from an object in front of said light source;
`means for automatically adjusting said duty cycle in
`response to the measured intensity of reflected light;
`a memory device for storing a first reflected light intensity
`value;
`a comparator for comparing said first stored intensity
`value with a second reflected light intensity value, said
`comparator outputting a comparison value to said
`means for automatically adjusting in order to adjust
`said duty cycle so that said second reflected light
`intensity value is made substantially equal to said first
`stored intensity value;
`a means for deactivating said light when the suply voltage
`is less than a predefined minimum value;
`and a means for manually adjusting said duty cycle.
`2. A video lighthead comprising:
`a lighthead having a housing;
`a light source located in said housing;
`a pulse width modulation circuit for controlling said light
`source, wherein the brightness of said light is deter-
`mined by the duty cycle of said pulse width modulation
`circuit;
`a photo-sensor for measuring the intensity of light
`reflected from an object in front of said light source;
`means for automatically adjusting said duty cycle in
`response to the measured intensity of reflected light;
`means for manually adjusting said duty cycle;
`a memory device for storing the reflected light intensity
`value;
`a comparator for comparing said first stored intensity
`value with a second reflected light intensity value, said
`comparator outputting a comparison value to said
`means for automatically adjusting in order to adjust
`said duty cycle so that said second reflected light
`intensity value is made substantially equal to the first
`stored intensity value;
`and a means for deactivating said light when the supply
`voltage is less than a predefined minimum value.
`3. The lighthead of claim 2, further comprising a switch
`which toggles said lamphead between an automatic adjust-
`ment mode and a manual adjustment mode.
`4. The lighthead of claim 1, wherein said means for
`automatically adjusting said duty cycle adjusts said duty
`cycle in response to a change in the brightness of said light
`to thereby maintain a constant light brightness as a voltage
`supplied by a battery driving said light changes over time.
`5. A video lighthead comprising:
`a lighthead having a housing;
`a light source located in said housing;
`a pulse width modulation circuit for controlling said light
`source, wherein the brightness of said light is deter-
`mined by the duty cycle of said pulse width modulation
`circuit;
`a photo-sensor for measuring the intensity of light
`reflected from an object in front of said light source;
`
`8
`means for automatically adjusting said duty cycle in
`response to the measured intensity of reflected light;
`means for comparing the magnitude of a supply voltage
`driving said light with a predefined minimum value;
`means for deactivating said light when said supply volt-
`age is less than said predefined minimum value;
`a memory device for storing a first reflected light intensity
`value;
`a comparator for comparing said first stored intensity
`value with a second reflected light intensity value, said
`comparator outputting a comparison value to the means
`for automatically adjusting in order to adjust said duty
`cycle so that said second reflected light intensity value
`is made substantially equal to the first stored intensity
`value;
`and a means for manually adjusting said duty cycle.
`6. A method for automatically adjusting the intensity of
`light emitted by a lighthead comprising the steps of:
`(a) providing a pulse-width modulated light source with a
`controllable duty cycle;
`(b) retrieving a preset duty cycles;
`(c) setting the controllable duty cycle to said retrieved
`preset duty cycle;
`(d) measuring a first reflected light intensity from an
`object in front of said light source;
`(e) measuring a second reflected light intensity from said
`object in front of said light source;
`(f) comparing said measured second reflected light inten-
`sity with said measured first reflected intensity to
`produce a comparison signal;
`(g) adjusting said duty cycle in response to said compari-
`son signal;
`(h) repeating steps (f) and (g) until said measured second
`reflected light intensity substantially equals said mea-
`sured first reflected intensity; and
`the method further comprising the steps of:
`measuring the voltage applied to said light source;
`comparing said measured voltage to a predefined mini-
`mum value; and
`deactivating said light source if said measured voltage
`is less than or equal to said predefined minimum
`value.
`
`7. A method for automatically adjusting the intensity of
`light emitted by a lighthead comprising the steps of:
`(a) providing a pulse-width modulated light source with a
`controllable duty cycle;
`(b) measuring a first reflected light intensity from an
`object in front of said light source;
`(c) measuring a second reflected light intensity from said
`object in front of said light source;
`(d) comparing said measured second reflected light inten-
`sity with said measured first reflected light intensity to
`produce a comparison si