Patent Publication Number: US-8119974-B2

Title: Microprocessor based automatically dimmable eye protection device with interruption prevention

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present patent application is a divisional of U.S. application Ser. No. 11/820,059, filed on Jun. 18, 2007, now U.S. Pat. No. 7,755,019, which is a continuation of U.S. application Ser. No. 11/089,930, filed on May 5, 2005, now U.S. Pat. No. 7,232,988, which is a divisional patent application of U.S. application Ser. No. 10/741,622, filed on Dec. 19, 2003, now U.S. Pat. No. 6,884,987, which is a continuation in part of U.S. application Ser. No. 10/140,049 filed on May 3, 2002, now U.S. Pat. No. 6,881,939, which claims priority to the provisional patent application identified by U.S. Application No. 60/288,759, filed on May 5, 2001, the entire content of all applications set forth above are hereby incorporated herein by reference. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a block diagram of an eye protection device constructed in accordance with the present invention. 
       FIGS. 2A-2C  are a schematic diagram of a control circuit of the eye protection device depicted in  FIG. 1 . 
       FIGS. 3-13  are flow diagrams illustrating the logic flow of one preferred embodiment of the present invention. 
       FIG. 14  is front perspective view of the eye protection device. 
       FIG. 15  is a rear elevational view of the eye protection device depicted in  FIG. 14 . 
       FIG. 16  is a flow diagram illustrating the logic flow of one preferred embodiment of the present invention. 
       FIG. 17  is a front perspective view of another embodiment of the eye protection device. 
       FIG. 18  is a cross-sectional view of the eye protection device depicted in  FIG. 14 . 
       FIG. 19  is a cross-sectional view of another embodiment of the eye protection device. 
       FIG. 20  is a cross-sectional view of another embodiment of the eye protection device. 
       FIG. 21  is a cross-sectional view of another embodiment of the eye protection device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The eye protection device  10  is provided with a control circuit  12 , and a shutter assembly  14 . The shutter assembly  14  is an auto-darkening filter capable of being driven between a “clear state” and a “dark state”. In the clear state, an individual can see through the shutter assembly  14  under ambient light conditions. In the dark state, the shutter assembly  14  typically becomes opaque so that the individual can only see through the shutter assembly  14  in the presence of an intense light, such as a welding arc. As will be discussed in more detail below, the opacity of the shutter assembly  14  can be varied. 
     The switching speed of the eye protection device  10  is an important performance attribute of the eye protection device  10 . As will be well understood by those skilled in the art, the switching speed is the time period for switching the shutter assembly  14  from the clear state to the dark state. As will be discussed in more detail below, in accordance with the present invention, a “dark state” drive signal having a high voltage pulse, e.g. 30-45 V, is provided to the shutter assembly  14  to enhance the switching speed of the shutter assembly  14 . The shutter assembly  14  is preferably a liquid crystal display, such as a twisted nematic liquid crystal display or a pi-cell liquid crystal display. 
     The control circuit  12  senses the intense light and outputs the “dark state” drive signal to the shutter assembly  14  to cause the shutter assembly  14  to switch from the clear state to the dark state. If the control circuit  12  senses that no welding arc is present, the control circuit  12  will cause a “clear state” drive signal to be delivered to the shutter assembly  14 . 
     The control circuit  12  includes a sensor circuit  16 , a weld detect circuit  18 , a microcontroller  20 , a user interface  22 , a display  24 , a power supply  26 , a voltage regulator  28 , a shade control  30 , a dark/light control  32 , a driver  34 , a variable high voltage regulator  36 , a low voltage regulator  38 , and a high voltage control  40 . As will be discussed in more detail below, in accordance with the present invention, the control circuit  12  provides a variety of useful features not available in analog control circuits. That is, the microcontroller  20  can learn, and store information so as to provide features such as automatic light sensitivity, automatic shade control, memory presets, and selectable torch shade settings. 
     The microcontroller  20  can be implemented as a microcontroller, a microprocessor having internal or external circuitry to function as a microcontroller, or a microcontroller/ASIC having internal or external circuitry to function as a microcontroller. 
     The power supply  26  includes a battery power supply  50 , and a solar power supply  54 . The battery power supply  50  and the solar power supply  54  provide electrical power to the voltage regulator  28  via a power line  56 . 
     The battery power supply  50  can be provided with any suitable voltage so as to supply power to the control circuit  12  and the shutter assembly  14 . For example, the battery power supply  50  can be provided with a voltage in a range from about 2.0 V to about 6.5 V. In a preferred embodiment depicted in  FIG. 2 , the battery power supply  50  has about 6 Volts. 
     The voltage regulator  28  receives the power generated by the battery power supply  50  and the solar power supply  54 . In response thereto, the voltage regulator  28  regulates the power to provide a stable voltage of preferably about 5 Volts. The voltage regulator  28  provides electrical power to all of the components in the control circuit  12 . 
     The sensor circuit  16  includes a plurality of sensors  60  for detecting the presence of light and outputting a sensor output signal representative of the level of light detected. The sensors  60  are preferably phototransistors. However, photodiodes or other types of light sensors could be used. 
     The sensor output signals are output to a plurality of signal filters  64  via signal paths  68 . The signal filters  64  are in series with the comparators  70 . The signal filters  64  are preferably high pass filters tuned at about 100-120 Hz so as to block ambient light signals formed by 50/60 Hz lighting. In accordance with the present invention, each of the signal filters  64  preferably include a resistor, positioned in parallel with the high pass filter so as to permit the signal filters  64  to pass at least some DC bias generated by the sensors  60 . Each of the high pass filters can be formed by a capacitor resistor circuit. The high pass filters allow AC signals to pass to a detection circuit, e.g., the comparator  70 , and thus the weld detect circuit  18  during AC welding. The high pass filters also provides the signal in the initial start of the weld because of the quick change in the light. The high pass filters rely on the signal caused by variations in the light while welding. During DC welding, the light is very smooth and little AC components are generated. Therefore, the resistor is added to allow DC biasing to affect the sensitivity. The brighter the light into the sensors  60 , the higher the DC component. Some of this bias is then passed to the detection circuit, e.g. the comparator  70 , via the resistor to increase the sensitivity and aid in the detection of the smooth weld. 
     The outputs of the signal filters  64  are fed to a plurality of comparators  70  via signal paths  72  to determine if the outputs of the signal filters  64  are above a predetermined threshold. The predetermined threshold will depend on the biasing level of the comparators  70  during ambient light conditions. For example, the sensitivity threshold can be in a range from about +0.5 V to about +1.75 V. The DC ambient bias level (from the resistor) can be in a range from about 0 V to about 0.5 V above the AC ambient bias level, e.g. +0.0 V to about +1.25 V of the comparators  70 . For instance, once the ambient biasing level exceeds the sensitivity threshold, the comparator  70  will output a signal causing the shutter assembly  14  to go dark. The outputs of the comparators  70  are ORed together. Thus, when the outputs of any one of the signal filters  64  are above the predetermined threshold, a signal is transmitted to the weld detect circuit  18  via signal paths  74  to cause a dark state drive signal to be delivered to the shutter assembly  14 . When the outputs are below the predetermined threshold, the weld detect circuit  18  will cause a “clear state” drive signal to be delivered to the shutter assembly  14 . 
     One preferred embodiment of the weld detect circuit  18  is shown in the schematic diagram of  FIG. 2 . The weld detect circuit  18  includes an electronic switch circuit, such as a transistor circuit, receiving the signal from the sensor circuit  16 . The electronic switch circuit includes an electronic switch, such as a transistor. In accordance with the present invention, a capacitor is connected in parallel with the electronic switch to increase the switching speed of the electronic switch circuit. For example, the electronic switch can be a transistor, and the capacitor can be connected between the collector of the transistor and ground. The electronic switch can be any suitable switching component, such as a transistor, a JFET, a MOSFET, or the like. 
     When the electronic switch circuit receives the signal indicative of the welding arc from the sensor circuit  16 , the capacitor  65  provides an initial high current spike to quickly change the state of the electronic switch. This initial high current spike increases the switching speed of the electronic switch so as to increase the switching speed of the eye protection device  10 . 
     The dark state drive signal is continuously generated by the variable high voltage regulator  36 . The clear state drive signal is continuously generated by the low voltage regulator  38 . When the shutter assembly  14  is a twisted nematic type LCD display, the low voltage regulator  38  can be omitted. The driver  34  simultaneously receives the dark state drive signal and the clear state drive signal and selectively passes the dark state drive signal or the clear state drive signal to the shutter assembly  14  so as to regulate the opacity of the shutter assembly  14 . The dark/light control  32  transmits signals to the driver  34  which controls passage of the clear state drive signal or the dark state drive signal through the driver  34 . 
     In one preferred embodiment, the driver  34  periodically switches the polarity of the clear state drive signal and the dark state drive signal so that the clear state and dark state drive signals transmitted to the shutter assembly  14  oscillate at any desired frequency. Typically, the frequency of oscillation will be between about 35 and 60 Hz. That is, if the oscillation of the clear state and dark state drive signals is below about 35 Hz, then the shutter assembly  14  may appear to flicker, which can be annoying for the user. If the oscillation of the clear state and dark state drive signals is above about 60 Hz, then the shutter assembly  14  will draw more power. If the shutter assembly  14  is a twisted nematic type of liquid crystal device, a desirable frequency of oscillation is about 35 to about 42 Hz. To further conserve power, the frequency of oscillation for the twisted nematic type of liquid crystal device can be as low as about 0.1 Hz. If the shutter assembly  14  is a Pi-cell type of liquid crystal device, a desirable frequency of oscillation is about 40 Hz to about 55 Hz. 
     The dark state drive signal is provided with two components; a HV pulse immediately followed by a constant voltage. The HV pulse is provided with a relatively high voltage in a range from about 30 V to about 120 V so as to quickly drive the shutter assembly  14  from the clear state to the dark state. The constant voltage has a reduced voltage preferably in a range from about 5 V to about 20 V to maintain the shutter assembly  14  in the dark state. The HV pulse preferably has a voltage in a range from about 15 V to about 120 V and a time period from about 10 microseconds to about 100 milliseconds. In general, the voltage of the HV pulse will depend on the maximum voltage ratings of the components utilized to implement the control circuit  12 . In one preferred embodiment, the voltage of the HV pulse is about 30-45 V, and the time period of the HV pulse is about 1-3 ms. When the shutter assembly  14  is a pi-cell liquid crystal display, the constant voltage can be in the range from about 5 V to about 20 V. 
     To increase the switching speed of the shutter assembly  14 , the variable high voltage regulator  36  continuously generates a first signal and a second signal having different voltages. The first signal is passed to the driver  34  for a selected time period to form the HV pulse, at the end of which the second signal is passed to the driver  34  to form the constant voltage. 
     In general, the HV control  40  communicates with the variable high voltage regulator  36  so as to control the switching of the first and second signals to form the HV pulse followed by the constant voltage. The HV control  40  can be formed by an RC circuit with the time constant of the RC circuit determining the time period of the HV pulse. The microcontroller  20  communicates with the HV control  40  when the eye protection device  10  is turned on so as to initialize the shutter assembly  14 . During initialization, the shutter assembly  14  is enabled to the dark state for a predetermined time period. In the preferred embodiment depicted in  FIG. 2 , the microcontroller  20  only communicates with the HV control  40  to initialize the shutter assembly  14 . 
     The shade control  30  adjusts the voltage level of the second signal so as to adjust the opacity of the shutter assembly  14  in the dark state. For example, the shade control  30  can be formed by a digital potentiometer positioned in a voltage divider circuit. 
     In use, when the eye protection device  10  is in a weld mode and the sensor output signal indicates to the weld detect circuit  18  that an intense light, such as a welding arc is present, the weld detect circuit  18  outputs a signal to the HV control  40  and the dark/light control  32  via signal paths  80  and  84  to simultaneously cause the variable high voltage regulator  36  to output the dark state drive signal, and the dark/light control  32  to switch the driver  34  to pass the dark state drive signal to the shutter assembly  14 . When the sensor output signal indicates to the weld detect circuit  18  that the intense light is no longer present, the weld detect circuit  18  outputs a signal to the dark/light control  32  to cause the dark/light control  32  to switch the driver  34  to pass the clear state drive signal to the shutter assembly  14 . As will be discussed in more detail below, the microcontroller  20  maintains the dark/light control  32  in the dark state for a predetermined delay period after the weld detect circuit  18  outputs the signal to the dark/light control  32 . 
     The microcontroller  20  receives user input from the user interface  22 . The user interface  22  can be any device capable of receiving user input, such as a keypad, microphone or the like. In a preferred embodiment shown in  FIG. 1 , the user interface  22  is provided with a keypad having a mode button  90  and an up/down button  94 . The mode button  90  permits selection of predetermined modes of operation, such as a sensitivity adjustment, a delay adjustment, a shade adjustment and a “3n1” adjustment. The up/down button  94  permits adjustment of selections in each of the modes. The mode button  90  can be implemented as a switch, or a knob, for example. The up/down button  94  can be implemented as a switch, a knob, two different buttons, an encoder or a toggle switch, for example. 
     The display  24  shows various information relating to the modes and selections in each of the modes. 
     The sensitivity adjustment permits manual selection of the sensitivity of the sensor circuit  16 . More particularly, the sensitivity of the sensor circuit  16  can be regulated by the microcontroller  20  by varying the predetermined threshold of the comparators  70 , as indicated by a signal path  96 . 
     The delay adjustment delays the passage of the clear state drive signal through the driver  34  for a selected time, thus preventing the shutter assembly  14  from switching to a clear state during brief “off” periods in the weld pulsations that exist with various weld types. Further, once the welding arc is extinguished, the work piece which is being welded may glow brightly for several milliseconds thereafter. The delay adjustment delays the clear state drive signal for the selected time so as to protect the individual&#39;s eyes from the glow of the work piece. The selected time is desirably between about 0.1 seconds to about 1 seconds. The selected time period for the delay can be set by a user utilizing the user interface  22 . The microcontroller  20  delays the passage of the clear state drive signal by controlling the dark/light control  32  and thereby delaying the passage of the clear state drive signal to the shutter assembly  14 . 
     The shade adjustment permits adjustment of the opacity of the shutter assembly  14  in the dark state. The shade adjustment is implemented by the microcontroller  20  controlling the shade control  30 . In one preferred embodiment, the shade control  30  is a digital potentiometer, which functions as a voltage divider to control the voltage of the variable high voltage regulator  36 . 
     The “3n1” adjustment permits selection of one of a plurality of modes referred to herein as a “torch mode”, a “grind mode” and a “weld mode”. 
     In the “torch mode” the microprocessor outputs a signal to the dark/light control  32  to maintain the shutter assembly  14  in the dark state regardless of the sensor output signal. In addition, in the “torch mode” the microprocessor outputs a signal to the shade control  30  to set the shade of the shutter assembly  14  to an opacity of about 5, 6, 7 or 8 so that the individual can see through the shutter assembly  14  when using a torch while still providing an adequate level of protection for the individual. The level of the shade control  30  in the torch mode can be predetermined and unchangeable by the user, or could be manually set by the user. For example, the level of the shade control  30  in the torch mode could be predetermined as a 5 or a 6. In this case, the user could not vary the level of the shade control  30 . Alternatively, the microcontroller  20  could be programmed to permit the user to manually set the level of the shade control  30  in the torch mode. 
     In the “grind mode”, the microcontroller  20  outputs a signal to the dark/light control  32  to maintain the shutter assembly  14  in the clear state regardless of the sensor output signal. In other words, in the grind mode, intense light caused by sparks, for example, will not switch the shutter assembly  14  to the dark state because the microcontroller  20  maintains the shutter assembly  14  in the clear state. 
     In the “weld mode”, the weld detect circuit  18  controls the dark/light control  32  as discussed above so as to immediately switch the shutter assembly  14  to the dark state when an intense light is sensed without the aid or help of the microcontroller  20 . 
     As discussed above, the microcontroller  20  can learn, and store information so as to provide other modes such as automatic light sensitivity, automatic shade control, memory presets, and selectable torch shade settings. These other modes can be selected via the mode button  90  or other input devices such as an external key. In the automatic light sensitivity mode, the microcontroller  20  continuously averages the light levels sensed by the sensor circuit  16 . The light sensitivity can be implemented in at least two manners. In the first manner, when the microcontroller  20  senses a jump in the light levels, then the microcontroller  20  outputs a signal to the dark/light control  32  to cause the shutter assembly  14  to switch to the dark state, and a signal to the HV control  40  to cause the HV pulse to be generated, as discussed above. In the second manner, the microcontroller  20  continuously averages the light levels sensed by the sensor circuit  16 , and automatically varies the bias level of the comparators  70  to change the sensitivity of the weld detect circuit  18 . 
     In the automatic shade control mode, the microcontroller  20  continuously monitors the intensity of the light once the shutter assembly  14  is switched to the dark state. The microcontroller  20  then controls the shade control  30  and varies the opacity of the shutter assembly  14  as the sensed light levels change so as to maintain a substantially constant amount of light passing through the shutter assembly  14 . 
     The microcontroller  20  can also be programmed to provide for a plurality of memory presets with each memory preset having at least one predetermined setting. For example, if two users were going to use the same eye protection device  10 , each user could have their own memory preset so that such users could select their memory preset before using the eye protection device  10 . In this case, the memory presets would reduce the amount of time spent on manually changing the settings. Alternatively or in addition, the microcontroller  20  could store a plurality of memory presets for one user. For example, the user could have one memory preset for TIG welding, and another memory preset for MIG welding. 
     The microcontroller  20  can also be programmed to monitor and store various parameters relating to historical use of the eye protection device  10 . For example, the parameters could be 1) unit on time, 2) unit dark time, and 3) average dark time. The stored parameters could be downloaded or viewed as an aid for monitoring working habits of the user, warranty returns, or troubleshooting. 
     The eye protection device  10  can also be provided with a communication device (not shown) for communicating with a computer, such as a personal computer, mini computer, mainframe computer, palm computer or personal data assistant. The communication device can be a wireless communication device, such as an optical link, or another type of communication device, such as a modem. The communication device can be used for downloading various parameters or data stored in the eye protection device  10  to the computer so that such parameters or data can be reviewed or used for other applications. Or, the communication device could be used to upload new programming, or settings to the eye protection device  10 . The new programming or settings could be used to upgrade the eye protection device  10  to provide new modes or functions. Alternatively, the new programming or settings could be used to provide new settings based on such factors as type of lighting. Further, the microcontroller  20  can be programmed to provide a self-test mode, and to display an indication of expected battery life on the display  24 . In the self-test mode, the microcontroller  20  would run tests on various components of the eye protection device  10 , such as the display  24 , the power supply  26  or the shutter assembly  14 . If any of the components are not working properly, an error code can be displayed by the display  24 . The expected battery life can be determined by monitoring the length of time that a battery has been installed (“actual length of time”) in the eye protection device  10 . By subtracting the actual length of time from a predetermined expected battery life, an estimated remaining battery life can be determined. The estimated remaining battery life is then displayed on the display  24  so as to communicate the estimated remaining battery life to the user. The estimated remaining battery life can also be determined by placing a predetermined load on the battery and then monitoring the decrease of the battery voltage during the load time. This is a well known method for measuring battery life. Thus, no further comments are deemed necessary to teach one skilled in the art how to use this method to estimate the remaining battery life. 
     To conserve energy, the microcontroller  20  is programmed with a sleep mode so as to reduce the amount of energy utilized when the microcontroller  20  is not in use. The microcontroller  20  continuously runs the programming for the sleep mode. In general, the microcontroller  20  is programmed to go to sleep when idle and wake up upon detection of certain predetermined events. The predetermined events can be 1) the detection of a weld, as discussed above, 2) the polarity of the dark state drive signal or the clear state drive signal needing to be switched, 3) the display  24  needing to be updated, and 4) the reception of a signal from the user interface  22 . 
     As discussed above, the polarity of the dark state drive signal or the clear state drive signal is switched about 70 to about 120 times per second. Thus, the sleep mode causes the microcontroller  20  to “wake up” at least about 70 to about 120 times per second (depending on the frequency of oscillation for the clear state and dark state drive signals), i.e., when needed to output a signal to the driver  34  and thereby switch the polarity of the dark state drive signal or the clear state drive signal. 
     Although in the preferred embodiment depicted in  FIGS. 14 and 15 , the control circuit  12  and the shutter assembly  14  are positioned in a same housing  102 , it should be understood that the control circuit  12  and the shutter assembly  14  could also be positioned in different housings. For example, the control circuit  12  could be supported on the user&#39;s belt, while the shutter assembly  14  could be supported by the welding helmet. A cable could extend from the control circuit  12  to the shutter assembly  14  to transmit the dark state drive signal and the clear state drive signal to the shutter assembly  14 . Further, the input or controls for the control circuit  12  could be supported on the outside of the user&#39;s welding mask or helmet. 
     Shown in  FIG. 2A-2C  is one embodiment of the control circuit  12 . The control circuit  12  will now be described in more detail. 
     The sensor circuit  16  includes the plurality of sensors  60  for detecting the presence of light and outputting a sensor output signal representative of the level of light detected. The sensors  60  include one or more phototransistor D 2  with the output of the phototransistor D 2  coupled to feedback circuits  206 . The output of phototransistor D 10  is sent to line  68 . A load resistor R 1  is connected between line  68  and ground. The signal filter  64  couples line  68  to line  72 . Line  72  is connected to the noninverting input of amplifier  210 . Amplifier  210  is preferably configured as closed loop noninverting amplifier. The gain, and thus the sensitivity of the amplifier  210  is controlled via the line  96  and the feedback resistor R 2 . The output of amplifier  210  on line  74  serves as the sensor circuit output. Line  74  is connected to the input of the weld detect circuit  28 . 
     The feedback circuit  206  for the phototransistor D 2  comprises a resistor capacitor circuit  216  connected between the emitter of the phototransistor D 2  and ground, and a feedback transistor Q 4  having a base coupled to line  218  of the resistor capacitor circuit  216 , a collector coupled to the base of the phototransistor D 2 , and an emitter coupled to the ground via resistor R 3 . 
     Phototransistor D 2  serves as the weld sensor. It receives an input of incident light  220  and produces an output on line  68  representative of the intensity of the incident light. The phototransistor D 2  used in the present invention is preferably a planar phototransistor configured for a surface mount. The planar phototransistor is smaller than conventional metal can phototransistors, thus allowing a reduction in size of the unit in which the sensor circuit is implemented. While the metal can phototransistors used in the sensor circuits of the prior art had a thickness of about ½ inch, the planar phototransistors with a surface mount used in the present invention have a thickness of only about ¼ inch. This reduction is thickness allows the sensor circuit to be implemented into a smaller and sleeker unit. Further, the surface mount configuration of the phototransistor D 2  allows the phototransistor to be easily affixed to a circuit board. The inventor herein has found that the TEMT4700 silicon npn phototransistor manufactured by Vishay-Telefunken is an excellent phototransistor for the present invention as it has a smaller size than conventional metal can phototransistors and allows the sensor circuit to maintain a constant signal level without excessive loading or the drawing of excessive current. 
     The resistor capacitor circuit  216  and the feedback transistor Q 4  in the phototransistor feedback circuit  206  function to adjust the sensitivity of the phototransistor D 2 . The resistors R 4  and R 5  and capacitor C 1  are chosen to be of a size to provide a relatively large time constant, and therefore a relatively slow response to changes in voltage on line  68 . The delay exists because of the time it takes for the voltage on line  218  to charge to an amount sufficiently large to activate Q 4 . Exemplary values for R 5  and R 4  are 1 MW and 2 MW respectively. An exemplary value for C 1  is 0.1 mF. A detailed description of the operation of the resistor capacitor circuit  216  and feedback transistor Q 4  can be found in prior U.S. Pat. Nos. 5,248,880 and 5,252,817, the disclosures of which have been incorporated by reference. 
     The signal on line  68  is fed into the amplifier  210 . The signal is first passed through the high pass circuit (signal filter  64 ) formed by capacitor C 2  to block the DC component of the detected signal. Line  72  contains the DC blocked detected signal. The current on line  72  is diverted to ground via resistor R 6 . 
     The sensor circuit  16  operates in the presence of both AC welds and DC welds. In an AC weld (also known as a MIG weld), the welding light is pulsating. Thus, the phototransistor D 2  will detect a pulsating light signal. The frequency of the pulsations is often 120 Hz. In a DC weld (also known as a TIG weld), the welding light is substantially continuous, with the exception of a small AC component. When an AC weld is present, the phototransistor D 2  will produce a pulsating output on line  68 . The variations in the voltage signal due to the pulses will be passed through the capacitor C 2  to line  72  and fed into the amplifier  210 . The amplifier  210  will then provide gain for the signal on line  74  which is sufficient to trigger the delivery of the “dark state” drive signal to the shutter assembly  14 . 
     When a DC weld is present, the phototransistor D 2  will quickly produce an output on line  68  catching the rising edge of the DC weld. This sudden rise in voltage on line  68  will be passed through to the amplifier  210  causing a signal on line  74  sufficient to trigger the delivery of a “dark state” drive signal to the shutter assembly  14 . Thereafter, capacitor C 2  will block the DC component of the DC weld, allowing only the AC variations in the DC weld to pass through to the amplifier  210 . A non-reactive element, e.g., resistor R 7 , is positioned in parallel with the high-pass filter circuit formed by the capacitor C 2 . The non-reactive element provides a DC bias to the input of the amplifier  210  to aid in the detection of the DC weld. That is, the brighter the light being generated from the weld becomes, the more sensitive the sensor circuit  16  becomes. In one embodiment, R 7  can have a value of 4.3 M ohm. The amplifier  210  can be a closed loop, noninverting amplifier. 
     As discussed above, the outputs of the comparators  70  are Ored together so that if any one of the comparators  70  detects a weld, the weld detect circuit 18  will be activated. The weld detect circuit 18  includes an electronic switch  250 , resistors R 10 , R 11  and R 12 , and capacitors C 5  and C 6 . When a weld is detected, the electronic switch  250  is activated through the resistor R 11 . The capacitor C 5  connected to the base of the electronic switch  250  discharges when the weld is detected and thereby enhances the switching speed of the electronic switch  250 . 
     When the electronic switch  250  switches, the capacitor C 6  discharges thereby causing a logical “low” to be transmitted. The capacitor C 6  and the resistor R 12  form an RC circuit having a time constant which causes the capacitor C 6  to charge at a predetermined rate. The signals received by the electronic switch  250  are typically in the form of short spikes caused by the sputtering of the weld. The time constant of the RC circuit should be tuned so that the output of the electronic switch  250  remains low between the spikes. The time constant can vary widely, however, a suitable time constant has been found to be between 1 and 100 milliseconds. 
     In response to the output of the electronic switch  250  going low, a signal is transmitted to the microcontroller  20  via a line  252 , and to the dark/light control  32  via a line A. The signal received by the microcontroller  20  interrupts the microcontroller  20  to wake up the microcontroller  20 . The microcontroller  20  then outputs a signal to the dark/light control  32  via a line  254 . Thus, either the weld detect circuit  18  or the microcontroller  20  can cause the dark/light control  32  to switch the shutter assembly to the dark state. 
     In particular, the low signal is output by the weld detect circuit  18  to one input of a nor gate  256 . In the weld mode, the other input of the nor gate  256  is held high. Thus, when the low signal is received by the nor gate  256 , the output of the nor gate  256  goes high. The output of the nor gate  256  is fed to an input of a nor gate  258 . The nor gate  258  has at least two inputs. One of the inputs is connected to the microcontroller  20  and the other input receives the output of the nor gate  256  as discussed above. The input of the nor gate  258  connected to the microcontroller  20  can be characterized as a hold dark, delay/torch line in that a high signal on such input will maintain the output of the nor gate  258  low, which in effect maintains the shutter assembly in the dark state. 
     The high signal provided to the nor gate  258  by the nor gate  256  causes the output of the nor gate  258  to go low. The low signal is provided to an inverter (formed by a nor gate  260  having both inputs tied together) which provides a high signal to a “high voltage in line” of the driver  34 . This causes the driver  34  to pass the dark state drive signal to the shutter assembly, rather than the clear state drive signal. 
     The output of the nor gate  260  is also provided to a capacitor C 8  of the HV control  40 . As discussed above, the HV control  40  communicates with the variable high voltage regulator  36  so as to control the switching of the first and second signals to form the HV pulse followed by the constant voltage. The HV control  40  can be formed by an RC circuit (shown as resistor R 14  and capacitor C 8 ) with the time constant of the RC circuit determining the time period of the HV pulse. The microcontroller  20  communicates with the HV control  40  via lines  270  and  272 ) when the eye protection device  10  is turned on so as to initialize the shutter assembly  14 . 
     During initialization, the shutter assembly  14  is enabled to the dark state for a predetermined time period. In the preferred embodiment depicted in  FIG. 2 , the microcontroller  20  only communicates with the HV control  40  to initialize the shutter assembly  14 . 
     The shade control  30  adjusts the voltage level of the second signal (shown as the line  274 ) so as to adjust the opacity of the shutter assembly  14  in the dark state. For example, the shade control  30  can be formed by a digital potentiometer  276  positioned in a voltage divider circuit formed with a resistor R 16 . 
     The logic flow of the microcontroller  20  of the eye protection device  10  is shown in  FIGS. 3-13 .  FIG. 3  shows a startup routine for initialization of the ports and determining whether to branch into an operational mode or a test mode.  FIG. 4  shows the logic for the operational mode of the microcontroller  20 .  FIG. 5  shows the logic for a decision making routine following the receipt of an interrupt.  FIG. 6  shows the logic flow when an interrupt occurred and such interrupt was not caused by the sensor circuit.  FIGS. 7 , and  9  show the logic flow to determine whether the up button, down button or function button was pressed and the action needed to be performed.  FIG. 10  shows the logic flow for a timer routine for toggling the shutter assembly  14  and the display at a periodic rate.  FIG. 11  shows the logic flow for updating information to the display.  FIG. 12  shows the logic flow of a power off routine.  FIG. 13  shows the logic flow for the test mode for calibrating the initial shade values. 
     Because the operation of microcontroller  20  utilized to implement the control circuit  12  may be affected by non-user activities, such as radiated electromagnetic fields produced during the welding process, such interferences with the operation of the microcontroller  20  can be compensated for within the logic flow of the microcontroller  20  of the eye protection device  10 . For example, in  FIG. 16 , shown therein is a logic flow for a startup routine for the microcontroller  20 . Determination of whether the startup of the microcontroller  20  was caused by user power-up (e.g. was caused by the on/mode button  90 , or another function key, being pressed), or was not caused by user power-up (e.g. was caused by a electromagnetic field interruption, timer reset, reset of CPU, loss of data, looping in a sub-routine or loss of timing) directs the branching of the logic flow, as indicated by a decision block  300 . Other examples of occurrences which may trigger a startup which are not a user power-up can include a reset of a CPU, loss of data, looping in a sub-routine, or loss of timing. 
     If the startup was caused by user power-up, then the logic branches to a plurality of initialization and calibration routines for the eye protection device  10 . If the startup was not caused by user power-up, then the initialization and calibration routines are bypassed and the logic branches to the main program for the operational mode of the microcontroller  20 , where the main program will run using the stored settings and parameters in use, or previously saved, prior to the startup of the microcontroller  20 . Thus, it can be seen that during use of the eye protection device  10 , if the operation of the microcontroller  20  is interrupted due to an electromagnetic field (or other non-user power-up), whereby the microcontroller  20  is caused to reset and startup, then the microcontroller  20  will not perform the initialization and calibration routines and will instead operate under the same settings and parameters as before the startup caused by the electromagnetic field interruption. As such, any customized settings or parameters set by the user will not be initialized back to default values or have to be reentered by the user, and the shutter assembly  14  will not be initialized and will continue operation from its current state. Further, since such an interruption and startup will be essentially instantaneous, the user will typically not detect such an interruption has occurred during use of the eye protection device  10  during the welding process. 
     Interference with the operation of the control circuit  12  from electromagnetic fields can also be reduced by providing a protective casing for at least a portion of the control circuit  12 . Shown, for example, in  FIGS. 17-21  is the eye protection device provided with a protective casing  304  disposed generally about the control circuit  12  to substantially prevent electromagnetic fields from a weld or from the welding equipment from interfering with the operation of the control circuit  12 . 
     In one preferred embodiment, the protective casing  304  comprises a non-conductive material  312 , wherein the non-conductive material  312  has a first surface  320  and a second surface  324 . A conductive material  316  is disposed on or in the non-conductive material  312 . The conductive material  316  may be disposed on the first surface  320  of the non-conductive material  312 , on the second surface  324  of the non-conductive material  312 , between the first surface  320  and the second surface  324  of the non-conductive material  312 , or combinations thereof. 
     The non-conductive material  312  may be any non-conductive material, or combinations of non-conductive materials, such as for example FR4, plastic, or combinations thereof. The conductive material  316  is preferably ungrounded and can be any conductive material, or combination of conductive materials, capable of impeding the transmission of electromagnetic fields. For example, the conductive material  316  can be chrome, nickel, copper, silver, tin, copper tape, conductive paint, or combinations thereof. In one preferred embodiment, the protective covering is disposed generally about the control circuit  12  and/or the microcontroller  20  so as to provide a Faraday cage generally about the control circuit  12  and/or the microcontroller  20 . 
     Further, when the control circuit  12  is supported by the housing  102 , such as shown in  FIGS. 18-19 , the non-conductive material  312  can be a non-conductive portion of the housing  102 . In one preferred embodiment, such as shown in  FIGS. 17-18 , the non-conductive material  312  is the housing  102  and the conductive material  316  is a chrome or nickel plating formed on the first surface  320  of the housing  102 . The plating can be formed from any suitable process, such as electroplating or glueing or molding conductive tape to the housing  102 . 
     In another embodiment, as shown in  FIG. 19 , the protective casing  304  comprises copper tape  328  disposed on portions of the second surface of the housing  102  generally adjacent the microcontroller  20 . Further, the protective casing  304  can also include copper tape  328  wrapped around at least one covered wire  414  of the control circuit  12 . In such an embodiment, the conductive material  316  of the protective casing  304  includes the copper tape  328 , and the non-conductive material  312  includes a non-conductive jacket (not shown) of the covered wire  414  of the control circuit  12 . 
     Although the protective casing  304  is depicted in  FIGS. 17-19  as including the housing  102  as at least a portion of the non-conductive material  312 , it should be understood that the non-conductive material  312  can include non-conductive material that is independent of the housing  102 . For example, as shown in  FIG. 20 , in one embodiment, the non-conductive material  312  of the protective casing  304  can be a separate housing disposed generally about at least a portion of the control circuit  12 , including the microcontroller  20 , and/or the user interface circuitry such as the keypad within the housing  102 . Further, in another embodiment, the non-conductive material  312  of the protective casing  304  can be disposed generally about at least a portion of the control circuit  12 , including the microcontroller  20 , outside the housing  102  when at least a portion of the control circuit  12  is disposed outside the housing  102 , such as shown for example in  FIG. 21 . Alternatively, the conductive material  316  could be embedded within the housing  102  or separate from the housing  102  and applied. 
     The embodiments of the invention discussed herein are intended to be illustrative and not limiting. Other embodiments of the invention will be obvious to those skilled in the art in view of the above disclosure. Changes may be made in the embodiments of the invention described herein, or in the parts or the elements of the embodiments described herein, or in the steps or sequence of steps of the methods described herein, without departing from the spirit and/or the scope of the invention as defined in the following claims.