Abstract:
A laser aiming light for firearms includes interchangeable switches for selectively limiting the laser output to an eye safe level for training purposes and for providing full power for operational use in a combat zone. A capability for using a remote switch is provided. As the output of the laser diode and associated components are temperature sensitive, temperature compensating circuitry ensures adequate power at high, as well as at low, ambient temperatures. Power is provided by enclosed conventional batteries retained by a sealed cap maintained in place by a pivotally mounted retainer and locking mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to laser aiming lights for firearms and, more particularly, to temperature compensating circuitry for maintaining the power level of a laser diode and associated components irrespective of changes in ambient temperature and to a removable fire and power mode selection switch.. 
     2. Description of Related Art 
     Conventional manually operated firearms have had since time immemorial mechanical sights for aiming the firearm. These sights require the user to visually align the sights with a target. Because of the slight angular deviations encountered in aligning mechanical sights, accuracy is compromised well short of the meaningful range of accuracy of the firearm and the associated projectile. To increase the range of accuracy, telescopic sights have been employed to obtain an effective range of accuracy of several hundred yards and which is, in part, a function of the muzzle velocity and type of firearm. Irrespective of whether mechanical sights or telescopic sights are used, the required visual alignment with the target creates a potentially life-threatening situation in a combat environment. That is, due to underbrush or other obstacles, visual alignment may not be quickly possible and the firearm may be momentarily useless. Furthermore, the likelihood of hitting a target is often a function of how steadily the firearm is held during the aiming and firing of the firearm. In critical situations, accuracy may be lost due to premature firing. 
     With the advent of small-sized lightweight laser diodes, associated circuitry and power supplies, aiming devices for firearms incorporating lasers came about. The frequency of the emitted aiming laser beam may be within or outside the visible spectrum. To ensure correspondence between the aiming laser beam and the trajectory of the projectile, the aiming laser beam may be bore sighted, as is well known. Such bore sighting is accurate to a certain range, which is a function of the type and nature of projectile, muzzle velocity and barrel configuration of the firearm. Most laser or infrared aiming beams incorporate adjustments for elevation and windage as a function of the range to the target and ambient climatological conditions, whereby accuracy at substantial ranges can be achieved. 
     A primary benefit of a laser aiming device is that the target is identified with a dot visible with goggles or the naked eye depending on whether or not the frequency of the laser beam is within the visible spectrum. When the dot is on a target, the firearm may be fired in whatever position it may be at that moment with a reasonable expectation that the projectile will hit the target. Thus, visual alignment of the firearm is no longer mandatory. If the laser aiming device emits radiant energy in the non-visible frequency range, the target will be unaware that a firearm is being aimed at it/him/her; necessarily, the user of the firearm must wear goggles of a type that will permit viewing the laser beam irradiating the target. 
     Combat units and others using laser aiming devices with their firearms conduct training exercises simulating combat. These exercises usually involve aiming the laser aiming devices at personnel. Since some combat environments require power levels that could cause permanent damage to one&#39;s eyesight unnecessary exposure to the likelihood of injury is present during training operations. To reduce the likelihood of injury during training, the power levels of the laser aiming devices must be prevented from exceeding a predetermined level (eye safe level). Usually, a switch on the laser aiming device permits selection of the output power at an eye safe level or at a maximum level. A danger of such prior art switches is that of inadvertently, by accident, or through forgetfulness, positioning the switch in the maximum power level position when it should be in the eye safe power level position. The resulting likelihood of injury to personnel of the opposing forces in a training exercise becomes very high and inexcusable. 
     Furthermore, the power output of laser diodes is essentially inversely proportional to temperature. When the output power is set at an eye safe level equal to or less than 0.7 milliwatts (mw) at a given ambient temperature, the power output may exceed this level upon a drop in temperature. To prevent the resulting possible hazard the output power should be prevented from increasing as a function of temperature. Thus, a benefit would be achieved if the laser aiming light maintained an essentially constant power output level irrespective of a drop of the ambient temperature. 
     When using laser aiming devices operating in the invisible spectrum, the user of the device must wear goggles of a type that will permit viewing of the irradiating laser beam. Far and away the most common of these devices is the class of night vision goggles that multiplies available light to produce an image of the scene being viewed. Because these devices operate on the principle of light amplification, under low light conditions such as under cloud cover or inside an enclosed structure, these devices are of limited use. Conversely, because of the ability of these devices to multiply available light thousands of times, any source of bright light in an otherwise low light scene will cause a bloom or glare similar of the kind encountered with an automobile&#39;s headlights on a dark night. Because of this glare, the viewing scene becomes washed in glare and features are indistinguishable. This condition is aggravated with the decrease in ambient light. Furthermore, the scene viewed through night vision goggles is monochromatic and many lack depth of field provided by a stereo graphic image. As a result, it is often difficult to visually acquire a dim aiming dot amid a highly textured scene such as a brushy field. As a result of these limitations in night vision technology, combat personnel using these devices need laser aimers that can be variably adjusted to compliment the limitations of night vision goggles rather than aggravate them. Thus, the optimum laser aiming device would have a variable intensity aiming dot that could be adjusted for range and light conditions so as to eliminate any “bloom”. Also, the optimum laser aiming device would include auxiliary illumination in the IR (infrared) spectrum to augment available light in low light conditions and provide primary light in conditions where ambient light is unavailable. Finally, the optimum laser aiming device would include a means of causing the aiming dot to pulse in order to facilitate quick visual acquisition in highly textured scenes. An additional benefit would be realized if the laser aimer provided multiple pulse rates so a group of personnel could work together and know which aim point was their own. 
     SUMMARY OF THE INVENTION 
     To ensure that a laser aiming device has sufficient power in any foreseeable temperature excursion environments, a temperature compensating circuitry is employed to increase the power applied to an associated laser diode to compensate for the reduced efficiency of the laser diode as a function of temperature increase. Thereby, the radiated laser beam emitted will have sufficient power to illuminate a target with a dot of radiated energy within the range of the firearm irrespective of the ambient temperature. Conversely, when temperature decreases and the laser diode efficiency increases, the temperature compensation circuit reduces power applied so as to maintain eye safe emissions. A switch removable and replaceable only upon dismounting of the laser aiming device from the firearm, determines whether the output power is at an eye safe level or at a maximum power level. By installing an eye safe switch for training exercises, it is impossible for the laser aiming device to emit sufficient power to cause injury to the eyesight of any personnel involved in the training exercise. In a combat environment, a switch permitting full power is installed. Depending upon various considerations of use, a switching capability exists to select continuous or pulsating emissions at one or more rates to help detect the location of the target irradiating beam and a selection of the amount of area illumination of a target by a high power infrared light emitting diode. Furthermore, a capability exists to adjustably select the radiated laser beam brightness to compensate for variations in operating environments. 
     It is therefore a primary object of the present invention to provide temperature compensating circuitry for a laser aiming device which ensures a constant power output irrespective of changes in the ambient temperature which is of particular concern when the laser aiming device is used in an eye safe mode. 
     Another object of the present invention is to provide circuitry to compensate for temperature related reduced or increased efficiency of a laser diode in a laser aiming device. 
     Still another object of the present invention is to provide a captured removable fire switch for a laser aiming device. 
     Yet another object of the present invention is to provide a remotely operated removable switch for a laser aiming device that cannot be pulled loose. 
     A further object of the present invention is to require replacement of a removable fire switch to switch operation of the laser aiming device between an eye safe mode and a full power mode. 
     A still further object of the present invention is to provide removable fire switches that limit the maximum power output when the laser aiming device is operated in either the eye safe mode or in the high power mode. 
     A still further object of the present invention is to provide a rotary up-down control to adjust aiming dot brightness. 
     A still further object of the present invention is to provide rotary switch for selecting a continuous, slow pulse rate or fast pulse rate beam of a laser aiming device. 
     A still further object of the present invention is to provide the capability of selectively illuminating a target with a low or a higher intensity infrared LED as a light source. 
     A still further object of the present invention is to provide an integral rigid mounting system that allows the device to be quickly and accurately mounted and dismounted from a weapon. 
     A yet further object of the present invention is to provide a method for operating a laser aiming device in different environments. 
     These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described with greater specificity and clarity with reference to the following drawings, in which: 
     FIG. 1 is a top view of a laser aiming device; 
     FIG. 2 is a left side view of the laser aiming device; 
     FIG. 3 is a bottom view of the laser aiming device; 
     FIG. 4 is an exploded view of the laser aiming device and a removable switch; 
     FIG. 5 is an exploded view illustrating the relationships between the laser aiming device, the removable switch, and a mount on a firearm; 
     FIG. 6 illustrates the laser aiming device mounted on a firearm; 
     FIG. 7A illustrates the laser aiming device with a removable switch; 
     FIG. 7B illustrates the laser aiming device with a removable remote switch; 
     FIG. 8 is an exploded view of the components of the removable switch; 
     FIG. 9 illustrates the electrical contacts in the laser aiming device associated with the removable switch upon engagement therewith; 
     FIG. 10 illustrates a rear view of the laser aiming device with the removable switch installed; 
     FIG. 11 illustrates the battery and removable cap associated with the laser aiming device; 
     FIG. 12 is an exploded view of the battery compartment sealing mechanisms and shrouds for the elevation and windage adjustments; 
     FIG. 13 is an exploded view illustrating the primary top, bottom and interior parts of the laser aiming device; 
     FIG. 14 illustrates a temperature compensation circuit; 
     FIG. 15 illustrates the drive circuit and the photo-diode feedback circuit; 
     FIG. 16 illustrates the timing circuit, the LED control circuit and the up/down power control circuit; 
     FIGS. 17A and 17B illustrates connections to various components; 
     FIG. 18 illustrates reverse battery, low battery, system lockout and fire switch circuits; and 
     FIG. 19 illustrates the electrical connection between the circuit shown in FIG.  15  and switch  30  shown in FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring jointly to FIGS. 1 and 2, there is illustrated a laser aiming device  10  for use with firearms to illuminate a target. The radiated beam may be visible or of a frequency outside the scope of the visible spectrum. In the latter event, a user must employ goggles of the type rendering the radiated beam visible. The device includes a body  12  having a laser aperture generally identified by numeral  14  through which the radiated beam is passed. To align the device with the trajectory of a projectile fired from a firearm to which the device is attached, bore sighting may be used. Bore sight alignment is effective for a limited range as a function of the nature of the firearm, the muzzle velocity of the projectile, and the projectile itself To accommodate for greater ranges, compensation for projectile drop (elevation) and windage must be made. Toward this end, device  10  includes a thumb wheel  16  to adjust for elevation and a further thumb wheel  18  to adjust for windage. A shroud  20  is used in conjunction with thumb wheel  16  and a similar shroud  22  is used in conjunction with thumb wheel  18  to shield the thumb wheels and yet permit manual access to the respective thumb wheels. At the rear of body  12  and visually accessible to a user, a rotary switch  24  permits adjustment of the intensity of the laser aiming beam emitted by the laser diode. A further rotary switch  26  may be employed as a system off switch and to control emission of the laser aiming beam between continuous, slow pulse or fast pulse. Moreover, the level of auxiliary illumination provided by an illuminating LED (LED  138  shown in FIG. 11) to augment light for night vision operations may be set therewith; in this position of rotary switch  26 , the laser aiming beam would be continuous and not pulsed. 
     In a combat environment, the most important criteria attendant laser aiming device  10  is that of the beam irradiating the target. Above a certain power level, the beam will cause irreparable damage to the eye if the beam should strike the eye. The resulting injury is not of consequence in a combat environment but it is unacceptable in a training environment. Accordingly, a removable switch  30  is used to set the maximum power level available from the laser diode generating the beam of visible or non-visible light. As will be described below with further joint reference to FIGS. 3,  4 ,  5  and  6 , removal/replacement of switch  30  is only possible by demounting device  10  from an associated firearm. The purpose for switch  30  is to act as a “fire switch” for actuating operation of the laser aiming device after it has been turned on. 
     Referring jointly to FIGS. 3 and 4, there are shown a bottom view and a perspective view, respectively, of laser aiming device  10 . On the bottom of body  12 , a V-shaped groove  32  is formed on one side and faces an inclined surface  34 . Firearms, such as firearm  36  shown in FIGS. 5 and 6 has mounted thereon a Weaver style mount  38  disposed at the top of a barrel assembly  40 . The mount includes inclined surfaces  42  mating with inclined surface  34  of body  12 . A laterally protruding ridge  44  is disposed on the side of mount  38  opposite from inclined surfaces  42 ; the cross-sectional configuration of ridge  44  mates with groove  32  in body  12  of laser aiming device  10 . A low profile lock mechanism  46 , operated by a lever  48 , extending from body  12  engages mount  38  to draw body  12  and the mount assembly to one another and thereby, with engagement of ridge  44  with groove  32  and inclined surfaces  34  with inclined surfaces  42 , rigidly lock laser aiming device  10  to firearm  36 . The resulting rigid mounting is critical to ensure accuracy of alignment despite manhandling of the associated firearm. Furthermore, the lever of the lock mechanism permits quick disconnect and repeatable accuracy for remounting the laser aiming device. Moreover, the low profile reduces the likelihood of the firearm catching on underbrush and the like. 
     Switch  30  includes a pair of studs  50 , 52  extending therefrom will engage a pair of slots  54 , 56  formed as part of mount  38 . Upon mounting of switch  30  into laser aiming device  10  and mounting the device upon the firearm, studs  50 , 52  engage slots  54 , 56  and preclude removal of switch  30  except upon dismounting of device  10  from the firearm. Thereby, the maximum power level to be emitted by the laser aiming device and controlled by switch  30  cannot be altered by a user except upon dismounting the laser aiming device and thereafter exchanging one switch  30  for another. 
     Referring jointly to FIGS. 7A,  8  and  9 , further details attendant switch  30  will be described. The switch includes a body  60  having a pair of tangs  62 , 64  at the upper end. A grip  66 , including a flexible membrane  67 , is disposed at the lower end to aid in inserting and withdrawing tangs  62 , 64  from within cavities  68 , 70  (See FIG.  9 ), respectively, in body  12 . A plurality of electrically conductive traces  74 A/P 61 ,  76 A,  78 A, and  80 A/P 71  are supported upon plates  74 ,  76 ,  78  and  80 , respectively, of a dielectric board  81 . Because these traces appear on the back side of the respective plates, they are shown in dashed lines. In the embodiment of switch  30  used for the full power mode, traces  74 A/P 61  are interconnected by a jumper trace  83  and in the embodiment of the switch used for the eye safe mode jumper trace  83  is absent or cut, as represented by the “X”. A push button switch, the “fire” switch, which may be disk-shaped in configuration as illustrated, is electrically connected to traces  76 A and  78 A by conductors  82 ,  84 , respectively. Operation of push button switch  72  is accomplished by pressing on membrane  67 . By pressing the membrane to close the push button switch and electrically connect traces  76 A,  78 A, the laser aiming device is activated and becomes operational. A face plate  86  of electrically non-conductive material includes a cavity  88  for receiving push button switch  72 , and channels  90 , 92  for receiving representative conductors  82 , 84 . The face plate includes a plurality of fingers  94 , 96 , 98  and  100  having studs  102  for engaging corresponding apertures  104  and indentations  107  in plates  74 , 76 , 78  and  80 . Upon assembly of switch  30  push button switch  72  will nest in cavity  88  and conductors  82 , 84  will be in channels  90 , 92  of face plate  86 . Parts of traces  74 A/P 61 ,  76 A will be exposed through slot  105  between fingers  94 , 96 . Similarly, parts of traces  78 A,  80 A/P 73  will be exposed through slot  106  between fingers  98 , 100 . Upon assembly of the three major components of switch  30 , fingers  74 , 76  will be lodged within channel  108  of tang  62 , which channel includes a groove  110  corresponding with slot  112  between plates  74 , 76 . Similarly, channel  114  in tang  64  receives plates  78 , 80 . Groove  116  in the channel corresponds with slot  118  between these two plates. Because face plate  86  is of dielectric material, access to the electrical components of switch  30  is only available via slots  105 , 106 , in face plate  86  to one or the other of the traces corresponding with each slot. 
     Referring specifically to FIG. 9, cavity  68  includes an electrically conducting element  120  (corresponding with conductor P 3 A shown in FIG.  15 ), which may be a plate or a wire and a further electrically conducting element  122  (corresponding with conductor FS 1  shown in FIG.  18 ), which may be a plate or a wire. Upon insertion of tang  62  into cavity  68 , exposed plate  74  will come into electrical contact with element  120  and plate  76  will come into electrical contact with element  122 . Similarly, cavity  70  includes an element  124  (corresponding with conductor FS 2  shown in FIG. 18) and an element  126  (corresponding with conductor P 3 B shown in FIG.  15 ), each of which may be a plate or a wire electrically contact plates  78 , 80 , respectively, upon insertion of tang  64  within the cavity. 
     FIG. 7B illustrates a laser aiming device  10  having a remote fire switch  130  which is a variant of fire switch  30 . The remote switch includes essentially all of the components of switch  30  described above with the following exceptions. Grip  66  is eliminated. A push button switch  132 , or the like, is electrically connected to body  134  of switch  130  via an electrical conductor  136 . The function of push button switch  132  is duplicative of push button switch  72  (see FIG.  8 ). Depending upon the nature of the firearm with which laser aiming device  10  is used and the position of the user, access to switch  30  might not be convenient or possible. In such event, switch  30  would be replaced by switch  130  and push button switch  132  would be located remote from the laser aiming device at a location accessible to the user to permit actuating (firing) the laser aiming device from the remote location. The remaining benefits and safeguards attendant switch  30  are incorporated in remote switch  130 . 
     FIG. 10 illustrates a proximal view of laser aiming device  10  to permit a user to make certain adjustments of the power and nature of the emitted laser beam and target illuminating element. As discussed above, switch  24  may be rotated clockwise to increase the power and counter-clockwise to decrease the power of the aiming laser beam as a function of range of interest and to control bloom. Switch  26  may be rotated clockwise to energize the laser aiming device and to select a continuous beam (SW 0 ), a slow pulse rate beam (SW 1 ) or a fast pulse rate beam (SW 2 ). Moreover, the amount of auxiliary/area illumination provided by illuminating LED  138  may be selected between a low level of illumination (SW 3 ) and a high level of illumination (SW 4 ). Preferably LED 138  is a high power infrared LED. One of its purposes is to provide covert illumination for night vision operations in extreme low light conditions. Red LED  139  functions to warn the user of a potentially dangerous low battery condition by turning on when battery voltage has decreased to 2.8 volts. 
     Referring jointly to FIGS. 11 and 12, features attendant the battery compartment for the batteries that serve as a  3  volt power source for the laser aiming device will be described in further detail. A battery compartment  140  is configured to receive two conventional AA batteries  142 , 144 . As is well known, humidity and the presence of water will corrode and possibly short the batteries and render them useless as a power source. It is therefore mandatory that battery compartment  140  be hermetically sealed at the point of entry and removal of the batteries. Moreover, precautions must exist to prevent inadvertent loss of the batteries and yet permit rapid replacement in a comb at situation. A cap  146  is inserted within mouth  148  of battery compartment  140 . The cap includes an O-ring  150  extending thereabout for sealed engagement with mouth  148  to prevent incursion of water. The cap is retained in place by a pivotally mounted lever  152  having a partially circular indentation  154  for engagement with a raised land  156  on the cap; the configuration of the land mates with indentation  154 . Upon engagement of lever  152  with cap  146 , the lever bears against surface  158  to prevent withdrawal of cap  146  from mouth  148 . To prevent inadvertent raising of lever  152  and corresponding pivotal movement away from engagement with cap  146 , a locking mechanism is provided. This locking mechanism includes a pin  160  extending from lever  152 . A catch  162  is pivotally mounted on cap  146 . After rotation of lever  152  in a counter-clockwise direction to engage and retain cap  146 , catch  162  is rotated in a counter-clockwise direction to engage pin  160 . Upon such engagement with the pin, lever  152  is precluded from rotating in the clockwise direction. A retainer  164  and corresponding pin  166  to retain catch  162  are shown in FIG. 12. A cord  168  may be used to attach cap  146  to body  12 . 
     Referring to FIG. 13, there is shown an exploded view of certain of the components of body  12 . Housing  170  includes a circuit board containing the circuit shown in FIG. 18 which supports two pairs of spring loaded wires  174 , 176  and  178 , 180  mounted upon elements  182 , 184  secured to plate  172 . These wires  174 , 176 , 178  and  180  correspond with and may be the same as elements  120 , 122 , 124  and  126  shown in FIG.  10 . With such spring loading, electrical contact with the corresponding plates in switch  30  is assured. A circuit board  186  (representatively shown) housing the circuitry and components for the laser aiming device is mounted in housing  170 . A cover (bottom)  188  is secured to housing  170  by a plurality of bolts  190  or functionally similar attachment means. It may be noted that locking mechanism  46  is formed as part of cover  188 . The circuitry mounted on circuit board  186  will be described in further detail below. 
     The control circuit to be described has a temperature compensating circuit that counteracts the temperature coefficients of both the laser diode and the controlling drive electronics since a typical laser diode becomes less efficient (less light per current) at a high temperature and more efficient at a lower temperature. To counteract this change in efficiency and therefore effectiveness of the emitted beam, a temperature compensating reference voltage centered upon 1.2 volts has been employed. The amount of compensation per degree of temperature change is controllable to permit customizing the circuit for the type of laser diode beam used. During training exercises, the eye safe power output level provided by the circuit is used. The circuit includes a DC amplifier to amplify the monitor photo-diode output with the amplifier gain set to restrict the maximum laser output to less than 0.7 milliwatts (mw). The output of the amplifier is compared to the temperature compensating reference voltage to control the laser drive circuit. A timing circuit may also be employed to produce pulsed and non-pulsed beam emissions and circuitry is provided to control the degree of illumination provided by the light emitting diode (LED) and degree of laser aiming beam intensity. 
     Referring to FIG. 14, there is shown a temperature compensation circuit. Temperature compensation is accomplished by combining in a differential amplifier IC 3  (LM324) a temperature stabilized reference voltage from a compensated reference diode with the voltage from an uncompensated reference diode. In particular, the temperature stabilized reference voltage from compensated reference diode U 1  (LM4041) is fed to a voltage divider R 21 R 22 . The output of this divider is fed to pin  10  of IC 3  via resistor R 16 . The voltage of uncompensated reference diode D 3  (1N4148) (approximately 2.2 millivolt change in voltage drop per degree Centigrade) is fed via resistor R 15  to pin  9  of IC 3 . The differences between the two voltages on pins  9  and  10 , set by the voltage divider (R 21 ,R 22 ) is amplified in differential amplifier IC 3  with a gain set (by resistors R 12 , R 15 , R 16  and R 17 ) to provide the needed reference voltage change per degree Centigrade to compensate for the characteristics of the laser diode being used. The amplified voltage output (pin  8 ) is the temperature compensation reference voltage (TempCompVref) and is fed to a digital potentiometer U 2  (see FIG. 16) to obtain variable power control of the laser diode. The output (VpwrTcompRef) of the variable power control potentiometer U 2  is used as the temperature compensated reference voltage on pin  3  of IC 3  (see FIG.  15 ). 
     The drive circuit for laser diode P 2  is shown in FIG.  15 . The laser drive current is controlled by the voltages on the gates of field effect transistors T 2  and T 3 . This voltage is built up in the RC network consisting of resistor R 20  and capacitor C 5  fed by VCC. The amount of gate voltage is controlled by the output on pin  1  of IC 3  (LM324) to create a discharge path when the reference voltage (VpwrTcompRef) on pin  3  has been exceeded by the feedback voltage from the monitor photo-diode circuit, which is the input on pin  2  of IC 3 . The monitor photo-diode feedback circuit will be described below. The current allowed through the laser monitor photo-diode is proportional to the amount of laser light being emitted by the laser diode. This monitor photo-diode current is converted to a voltage by resistor R 8 , the high power limit trimpot. This voltage is fed into DC gain amplifier IC 3 . The gain setting for this amplifier is set to 1 for high power mode (when P 3   a  and P 3   b  are shorted) and to a multiple (set by trimpot resistor R 14 , resistor R 7 , resistor R 5  and capacitor C 3 ) for the eye safe mode (when P 3  and P 3   b  are open). 
     The output of amplifier IC 3  on pin  14  is fed into the drive circuit, pin  2  of IC 3  to be compared to the temperature compensated reference voltage (VtpwrTcompRef) present on pin  3  of IC 3  for controlling the laser light emitted. 
     The timing circuit is illustrated in FIG.  16 . It includes an integrated circuit IC 1 , resistor R 13 , resistor R 6 , resistor R 18 , capacitor C 1 , capacitor C 6 , capacitor C 4 , switch SW 0 , switch SW 1 , switch SW 2 , and transistor Q 1 . The core of this circuit is IC 1  which is a  555  timer. When the output of IC 1  is high, the laser diode shuts off and when the output of IC 1  is low, the laser diode is on. The time periods are set with resistors R 13 , resistor R 6  and either capacitor C 4  when switch SW 1  is on or capacitor C 6  when switch SW 2  is on. For continuous operation, the reset pin of IC 1  is clamped to ground which causes the output of IC 1  to stay low as long as the reset is low. Resistor R 18  is a pullup resistor to return the reset to high when the reset pin is not clamped to ground. These various timing signals control the on-off operation of the laser by clamping the reference voltage to ground through transistor Q 1 . 
     The LED control circuit will also be described with reference to FIG.  16  and includes transistor T 5 , transistor T 6 , resistor R 11 , resistor R 4 , switch SW 4 , switch SW 3 , and the LED. When switch SW 3  is closed, field effect transistor T 6  is turned on to allow current to flow through resistor R 11  to the LED. Resistor R 11  limits the current to provide a low level of illumination. Switch SW 3  also sets IC 1 &#39;s reset low to cause the laser to have a continuous output. When switch SW 4  is closed, field effect transistor T 5  is turned on allowing current to flow through resistor R 4  to the LED. Resistor R 4  limits the current to provide a high level of illumination. Switch SW 4  also resets IC 1 &#39;s reset low causing the laser to have a continuous output. 
     The power control circuit is also described in FIG.  16  and includes digital potentiometer U 2  and resistor R 3  and a momentary power increase/power decrease (/IPOWER/DPOWER switch). The temperature compensation reference voltage (TempCompVref) is fed to digital potentiometer U 2  which is used with resistor R 1  as a voltage divider. The resistance of resistor R 1  is chosen to limit the low end resistance of this voltage divider to guarantee a minimum low limit of operation of the laser diode. The output power at wiper pin  6  is used as the reference voltage (VpwrTcompRef) for the laser drive circuit. When the incrementing power switch (/IPOWER) is closed, the digital potentiometer gradually increments to a higher setting resulting in a higher reference voltage for the laser drive circuit. When the decrementing power switch (Dpower) is closed, the digital potentiometer gradually increments to a lower setting resulting in a lower reference voltage (down to the limit set by resistor R 1 ) for the laser drive circuit. This raising and lowering of the reference voltage causes proportional changes in the output power of the laser diode. 
     Resistor arrays AR 1  and AR 2  are used as pullups for switches SW 0 , SW 1 , SW 2 , SW 3  and SW 4  and for /IPOWER; see FIG.  17 A. Resistors R 19  (FIG. 16) and resistors R 23 , R 24  (See FIG. 17B) are not normally used; their function is to disable or alter functions of the system. 
     FIG. 18 illustrates reverse battery, low battery warning, system lockout, and fire switch circuits. The reverse battery protection circuit consists of pins  1 ,  2 ,  7 , and  8  of transistor U 101 . This is accomplished by passing system current through a P-channel FET has a low forward voltage drop. By connecting the positive terminal of the battery to the FET source (pin  1 ) and the negative terminal to the FET gate (pin 2 ) allows current to flow through the FET as needed by the system. If the battery is reversed, no current will flow to the system. 
     The low battery warning circuit consists of IC 102 , resistor R 104 , resistor R 101 , capacitor C 103 , transistor T 102 , resistor R 106 , and LED D 101 . The IC is an active high reset generator with a reset voltage of 2.63 volts. The sense voltage at pin  3  of IC 102  is derived from a voltage divider consisting of resistor R 104  and resistor R 101 . Capacitor C 103  stores the sense voltage to reduce power switch noise. D 101  is an LED indicator ( 139  shown in FIG. 10) that has its current limited by resistor R 106  to obtain a desired brightness and is switched on with N-channel FET transistor T 102  when a low voltage battery condition exists. That is, as the system voltage drops to approximately 2.8 volts, the sense voltage at the voltage divider drops to less than 2.63 volts. This causes the reset generator to go to an active high state which switches transistor T 102  on and allows current to flow through the LED ( 139  shown in FIG. 10) to indicate a low voltage condition. 
     The system lockout circuit consists of resistor R 102 , resistor R 107 , IC 101 , capacitor C 104 , and transistor T 101 . IC 101  is a 2.63 volt active low reset generator. Resistor R 102  is a current limiting resistor to reset the generator. Resistor R 107  is a pulldown resistor assuring that pin  1  on transistor T 101  goes low during reset. Capacitor C 104  stores the system voltage sensed by the reset generator to reduce power switch noise. When the system voltage drops below 2.63 volts, the reset generator goes to its active low state which turns off transistor T 101  and disconnects fire switch FS 2  from ground. Thereby, the fire switch circuit, FS 1 , FS 2  is prevented from activating transistor U 101 . 
     The fire switch circuit consists of resistor R 103 , fire switch FS 1 , fire switch FS 2 , and pins  3 ,  4 ,  5 , and  6  of transistor U 101 . Transistor U 101  is a P-channel FET. Resistor R 103  is a pullup resistor for gate pin  4  assuring a high state when five switches FS 1  and FS 2  are not shorted,  5  thereby turning off transistor U 101 . When gate pin  4  of transistor U 101  is grounded, transistor U 101  will turn on and supply VCC to the main system circuit board. Shorting five switches FS 1  and FS 2  will ground pin  4  of transistor U 101  as long as the system voltage is above 2.63 volts. When the system voltage drops below 2.63 volts, the path to ground through transistor T 101  is removed. 
     While the invention has been described with reference to several particular embodiments thereof, those skilled in the art will be able to make the various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention. It is intended that all combinations of elements and steps which perform substantially the same function in substantially the same way to achieve the same result are within the scope of the invention.