Patent Publication Number: US-9903687-B2

Title: Compact spring guide rod laser

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/105,721 filed Jan. 20, 2015. 
    
    
     FIELD OF THE INVENTION 
     This invention relates, in general, to laser sights for firearms, and, in particular, to self-aligned laser sights which are easily installed, are ambidextrously operated, and have prolonged battery life. 
     BACKGROUND 
     In U.S. Pat. No. 4,934,086, there is shown a firearm, in particular a pistol, in which a laser sight is mounted in a recoil spring guide chamber. Laser sights are often used by law enforcement authorities in order to enhance the negotiating position of a law enforcement officer when confronting a party subject to arrest. It is reported that once a party subject to arrest recognizes that the party has been targeted with a laser sight, such parties often cease further resistance to arrest and relinquish their own firearms. So, there is a need for a laser sight in such situations. 
     Certain firearms are not equipped with safety latches. Law enforcement officers are trained to withdraw such a firearm from its holster and place a trigger finger along the recoil spring guide chamber of the firearm. Such technique reduces the cases of inadvertent firing of the firearm. However, it would be desirable to provide the law enforcement officer with a positive reinforcement for this training technique. 
     There is also a need for a laser sight which may be quickly installed in a pistol without requiring substantial modification of the firearm. Most laser sights for pistols have been accessories that are added by the pistol owner and not by the manufacturer. Such laser sight accessories often require substantial modification of the pistol in order to accommodate the laser sight. In some cases, the modification the extent of the modifications is such that the pistol manufacturer will not further honor the original warranty that was made in connection with the sale of the pistol. Alternatively, lasers can be joined to an exterior of the firearm changing the size, weight and feel of the firearm and requiring use of non-standard holsters. As such, it is desirable to have a laser sight accessory which requires minimal modifications of the pistol so that the original manufacturer warranty is maintained and so that the laser sight can be rapidly installed by the pistol owner or user without requiring installation by a trained technician. 
     There has also developed a need for a long lasting laser sight. Because current lasers require substantial power, laser sights have been of unduly large size in order to accommodate power supplies needed to maintain the laser in an operating condition for a reasonable amount of time such as 30 minutes. So, the users of laser sights have been faced with the dilemma of shrinking the size of the laser sight but reducing the overall operating life of the battery or having a larger sight that can accommodate a larger battery and thus a longer life. As such, there is a need for a relatively small laser sight with a small power source or battery that lasts for 30 minutes or more. 
     U.S. Pat. No. 5,509,226 describes one solution to this problem—the spring guide rod laser. This patent describes a laser sight that is disposed substantially entirely within the recoil spring guide chamber of a firearm, such as the recoil cavity of a pistol. As is schematically illustrated in  FIGS. 1A and 1B  this prior art spring guide rod laser sight  2  has a housing  4  with the following components arranged from back to front—batteries  6  that are electrically connected at one terminal to a battery pin  9  and at another terminal to a high value capacitor  8 . A control circuit  10  is electrically connected battery pin  9  by way of capacitor  8 . Three leads  11  are carefully soldered to provide a path between control circuit  10  and a laser  12 . 
     Laser  12  generates light when activated by control circuit  10  and this light passes through optics  14  to create a more collimated laser emission. In a spring guide rod laser, housing  4  is sized and shaped based upon a recoil spring guide rod for a firearm and can be substituted for the manufacturer&#39;s recoil spring guide rod. A portion of housing  4  proximate lens  14  extends outside of the firearm so that light emitted by laser  12  passes outside of the firearm. Because the spring guide rod is typically co-aligned with an axis of a barrel of a firearm light from the laser is typically placed proximate where a firearm will fire. 
     A modified take down latch  16  on the firearm is movable from an off position shown in  FIG. 1A  where a non-conductive portion  18  of a take down latch  16  blocks current from traveling between a battery pin and a conductive path  24  leading to laser  12  and a position where a closed circuit can exist between batteries  6 , a battery pin  9 , a first conductive surface  14 , a second conductive surface  22 , a conductive path  24 , and laser  12 . In  FIGS. 1A and 1B  conductive path  24  is shown in block form but includes components of the firearm in which spring guide rod laser sight  2  is located such as a recoil chamber of the firearm, and a recoil spring. This introduces potential variability in the electrical path complicating the design of spring guide rod laser sight  2 . 
     The spring guide rod laser allows a laser sight to be incorporated into a pistol without substantially changing the look, feel, or handling of the firearm. While such spring guide rod lasers are technically and commercially successful, it remains desirable to offer new models which can offer advantages such as reducing any or all of the size, complexity and cost of such spring guide rod lasers, reducing manufacturing and product costs, offering more user control over a mode of operation of the spring guide laser, providing improved electrical performance, or improving runtime performance. Of particular interest is making spring guide rod lasers available for use in smaller sized handguns that have relatively small guide rods. 
     Conventionally, there are many challenges in trying to improve upon the successful design of the prior art spring guide rod lasers. One problem faced is that the small batteries of a size that can be incorporated into a guide rod must also be of a type that is not rapidly self-discharging so that they can be incorporated into the spring guide rod laser and then used weeks, months or even years later. However, such batteries must also be capable of providing sufficient power to allow a laser to generate a laser beam that is visible from a great range when activated. This places a high drain on such batteries requiring significant capacitors that add size and weight to the spring guide rod laser. Additionally, the use of the take down latch and components of the firearm as conductive elements in the system can introduce resistance into the circuit at the points of contact between the spring guide rod laser and the firearm components as well as at points of contact between firearm components that are used to provide such electrical paths. This resistance can add to the burdens placed on the batteries and capacitors. 
     What are needed in the art are spring guide rod lasers that can overcome such difficulties to enable any of smaller, less expensive, more efficient, longer running, less complex and more feature rich spring guide rod lasers. 
     Additionally, it has been common for spring guide rod lasers of the prior art to have only one mode of operation—a periodic mode. There have been many reasons for this, one reason for this is that the drive circuit must reliably activate and operate as intended from a powered off state thus introducing mode selection can create unintended issues when start up occurs. Another reason for this is that it is not a trivial matter to provide user access to a mode selector that is to control a circuit that is housed within the central portion of a spring guide rod housing. It also will be understood that it is not a trivial matter to provide a mode selector that will maintain a setting even when exposed to the extreme environment within a firearm spring guide chamber. Further, there are users who will prefer to have the option to change settings without having to access the spring guide rod. 
     Thus what is also needed in the art is a compact, efficient, reliable, less complex and less expensive spring guide rod laser that can allow a user to select a mode of operation while the spring guide laser is installed in the firearm. 
     BRIEF SUMMARY OF THE INVENTION 
     Laser systems are provided. In one aspect a laser system has a battery unit and a transistor having a source and a drain in series with the laser and the battery unit with the laser with the transistor having a source, and a gate that allows sufficient current to flow to the laser to allow the laser to emit light when a voltage at the gate is at a higher level and that does not allow sufficient current to flow to allow the laser to emit light when a voltage at the gate is at a lower level. A microcontroller is operable in an active mode and a reduced power mode having an activation input connected to a switch, a reduced power input connected in parallel with the capacitor and an output connected to the gate. When the switch changes from a first state to a second state, the microcontroller enters an active mode generating a plurality of micro-pulses at the gate such that an active current is supplied that cause the laser to emit a continuous plurality of micro-pulses that when viewed by a human observer provide an apparently continuous laser pulse and when the microcontroller enters a power down mode, no micro-pulses are provided at the gate and a leakage current through the laser provides energy to maintain the processor in the power down mode of activation until the switch is again closed. 
     In another aspect a laser system comprises a housing operable as a spring guide rod in a firearm and having a first opening at a first end and a second end, a laser positioned in the housing to emit light from the first end of the housing, a control system positioned proximate second end and a battery unit between control system and the laser, the battery unit being electrically connected at a first terminal to a laser, and at a second terminal to the control system. The battery unit is electrically insulated from the housing and the laser and control system are electrically connected to the housing so that the control system can control operation of the laser by controlling current flow between the laser and the second terminal of the battery unit without current flowing through a firearm component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are block views of a prior art spring guide rod laser. 
         FIG. 2  illustrates a firearm. 
         FIG. 3  illustrates an electrical schematic for one embodiment of a circuit useful in a spring guide rod laser. 
         FIG. 4  is a flow chart for operating a spring guide rod laser. 
         FIGS. 5A and 5B  illustrate apparent laser illumination patterns. 
         FIGS. 6A and 6B  illustrate apparent laser illumination patterns and micro-pulses. 
         FIG. 7  illustrates another flow chart for a spring guide rod laser. 
         FIG. 8  illustrates an embodiment of a spring guide rod laser. 
         FIG. 9  illustrates an embodiment of a spring guide rod laser with a first switch arrangement in an open position. 
         FIG. 10  illustrates the spring guide rod laser of  FIG. 9  with the switch in a closed position. 
         FIG. 11  illustrates an embodiment of a spring guide rod laser with a second embodiment of a switch in an open position. 
         FIG. 12  illustrates the spring guide rod laser of  FIG. 11  with the switch in a closed position. 
         FIG. 13  illustrates an embodiment of a spring guide rod laser with a third embodiment of a switch in an open position. 
         FIG. 14  illustrates the spring guide rod laser of  FIG. 13  with the switch in a closed position. 
         FIGS. 15A and 15B  illustrate a first embodiment of a slide latch, housing and pin in a centered position and in a non-centered position. 
         FIGS. 15C and 15D  illustrate a second embodiment of a slide latch, housing and pin in a centered position and in a non-centered position. 
         FIGS. 15E and 15F  illustrate a third embodiment of a slide latch, housing and pin in a centered position and in a non-centered position. 
         FIG. 16  illustrates another embodiment of a driving circuit. 
         FIGS. 17A and 17B  illustrate an embodiment of a center-biased take down latch useful in a tap-on/tap-off type of spring guide rod laser sight. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 2  there is generally shown a firearm  30 . Typical of such a firearm is the Glock 17/17L/18/19/20/21 and 22 semi-automatic pistol manufactured by Glock, GMBH of Austria. In firearm  30 , a pistol grip frame  32  holds a magazine  34  which contains a number of rounds of ammunition. The ammunition is spring biased in a direction toward the structure  36  containing a reciprocating chamber. Cartridges from spent rounds are ejected through ejection slot  39  of structure  36  when structure  36  moves to the left or backward along axis  28  with respect to pistol grip frame  32  under the recoil action following discharge of firearm  30 . Structure  36  is coupled to pistol grip frame  32  via a take down latch  27  which is mated to a catch  29  that is integral with structure  36 . Disposed between structure  36  and frame  21  is a recoil chamber  23 . Within recoil chamber  23  is a spring guide rod laser sight  40  surrounded by a recoil spring  42 . 
     With reference to  FIG. 3  what is shown is a first embodiment of a driver circuit  50  for use in driving a laser  52  and that can usefully be employed for example in a spring guide rod laser sight  40 . In this embodiment, driver circuit  50  includes laser  52 , battery unit  54 , a transistor  56 , and a control system  60  comprising in this embodiment, a microcontroller  58 , a diode  62 , a first capacitor  64 , a second capacitor  66  and a switch  68 . Transistor  56  allows current to flow between source S and drain D in accordance with a voltage level at a gate G. When gate G is at a comparatively higher voltage level, current flows between source S and drain D such that laser  52  can emit light. When gate G is at a relatively low voltage level, there is insufficient current to allow laser  52  to emit light. Gate G is electrically connected to an output of microcontroller  58  such that microcontroller  58  can control the voltage at gate G. Gate G is also connect to ground by way of resistor  67  to help ensure that the voltage at gate G does not rise to the higher voltage level when microcontroller  58  is unpowered for example when battery unit  54  is being change or fully depleted. 
     In this embodiment, microcontroller  58  is selected from a class of microcontrollers that have low power consumption requirements examples of which include the programmable ATtiny4, ATtiny5, ATtiny 9 and ATtiny 10 microcontrollers sold by Atmel. This is not limiting and other microcontrollers of this class can be used. Such microcontrollers  58  can enter a power down mode that draws less than 1 microamp at 1.8 VDC. In the embodiment that is illustrated, diode  62  and capacitor  64  cooperate to maintain a voltage and a supply of current sufficient to maintain micro-controller  58  in the power down mode even when laser  52  is not emitting light. The current necessary to maintain a voltage across capacitor  64  is supplied by current leaks from battery unit  54  through laser  52 . This creates a supply of power across capacitor  64  that can supply the voltage and current required to keep microcontroller  58  in the power down mode for an extended period of time without fully draining battery unit  54 . It will be appreciated that when laser  52  is active, first capacitor  64  is effectively shunted. During such times, power to operate microcontroller  58  is supplied by power from capacitor  64 . Accordingly, capacitor  64  has sufficient capacity to operate microcontroller  58  for the extent of each micro-pulse. From this it will be appreciated that the use of micro-pulses  100  further allows capacitor  64  to be smaller than would be required in the event of continuous or pulsed operation of the prior art which requires emission pulses that can operate for substantial periods of time. 
     Given the low drain on battery unit  54  required to maintain microcontroller  58  in the powered down mode, it is possible for microcontroller  58  to remain in the powered down state for a significant period of time without exhausting battery unit  54 . This allows microcontroller  58  to transition from the powered down state to an idle mode or active mode in a manner that is more controlled than might occur if control system  60  required microcontroller  58  to transition to the active state by reactivating from an unpowered state. 
     Control system  60  has non-volatile memory  65  which in this embodiment is integrally located within microcontroller  58  but that in other embodiments may be external thereto. Non-volatile memory  65  is used to store programs that can be executed by microcontroller  58 . 
       FIG. 4  illustrates one example embodiment of a method for controlling laser  52 . As is shown in  FIG. 4 , the process begins with microcontroller  58  in a powered down mode. When switch  68  closes, microcontroller  58  activates and determines a laser appearance pattern (step  70 ). The laser appearance pattern is a pattern of light emission intensity changes that will be perceived by the human eye while observing the laser emission over time. This pattern of light emission may be a periodic perceived appearance pattern where the intensity of the observed light emitted by laser  52  appears to change periodically over time or a continuous apparent appearance pattern where the light emitted by laser  52  appears to be constant over time. Some firearm users prefer continuous light emission while others prefer periodic emission and still others prefer to select the pattern based upon a situation in which the laser will be used. 
       FIGS. 5A and 5B  respectively illustrate a periodic laser appearance pattern in which the laser emission appears and disappears at a frequency of, for example, about 10 Hz and a continuous laser appearance pattern in which the laser emission appears and maintain a substantially constant observable intensity from a moment of activation to a moment of deactivation of laser. As is shown in  FIG. 5A  in a periodic laser appearance pattern  90  an observer will perceive a laser dot from t 0  to t 1 , from t 2  to t 3  and from t 4  to t 5 . Conventional spring guide rod laser aiming devices have provided such periodic appearance patterns by drawing continuously on battery unit  54  from time t 0  to t 1 , from t 2  to t 3  and from t 4  to t 5 . The frequency of a periodic appearance pattern is one that is substantially recognizable to the human eye. Such frequency can be between 8 and 12 Hz and is preferably at approximately 10 Hz. Further, the periodic laser appearance pattern  90  may be chosen to be at a frequency and duty cycle that takes advantage of any refresh characteristic of battery unit  54 . 
     However, it will be understood that while periodic laser appearance patterns may offer some recovery time for a battery, they still impose significant draw on the battery during periods of activation simply by applying a continuous draw on battery unit  54  from t 0  to t 5  during active portions of their duty cycle. Such continuous draws can significantly reduce battery life. 
     To reduce this effect, prior art as shown in  FIGS. 1A and 1B  interposes a powerful capacitor  8  between batteries  6  and circuit  10 . Capacitor  8  reduces the extent of the drain on battery unit  54 . However, capacitor  8  typically occupies a significant portion of the volume within prior art housing  4 , and adds expense and complexity to the spring guide rod laser. 
     The inventors, however, have developed another approach based upon the unique characteristics of human visual perception. In this regard, it will be understood that human visual perception is a function of a process known as visual phototransduction by which light is converted by sensors in the eye into electrical signals usable by the human brain and by various memory and processing features and capabilities of the human brain. As a result the brain will perceive laser emitted light as being continuous under certain circumstances even when the light that is being emitted is not continuous. 
     What the inventors have determined that it is possible to use this characteristic of human visual perception to allow a spring guide rod laser to be operable in more than one mode to emit a laser beam that has either a continuous or a pulsed appearance without necessarily imposing a large continuous drain on batteries and while eliminating the need for high-capacity capacitors. In the embodiment illustrated in  FIGS. 3-9  this is done by driving laser  52  to generate very brief micro-pulses that are individually visually indistinguishable but are arranged to be emitted in serial so that when a series of these micro-pulses is viewed in sequence they have the appearance of a continuously emitted laser beam. 
       FIG. 6A  illustrates a pattern  102  of micro-pulses  100  that can be used to form periodic laser appearance pattern  90  of  FIG. 5A , while  FIG. 6B  illustrates a pattern  104  of micro-pulses  100  that can be used to form the continuous laser appearance pattern  92  of  FIG. 5B . In  FIG. 6A  an example micro-pulse pattern  102  is shown that comprises a first set  110  of micro-pulses  100  transmitted from t 0  to t 1  followed by an absence of pulses from t 1  to t 2 , a second set  112  of micro-pulses  100  transmitted from t 2  to t 3 , followed by an absence of pulses from t 3  to t 4  and a third set  114  of micro-pulses  100  transmitted from t 4  to t 5 . In  FIG. 6B , an example micro-pulse pattern  104  is shown that comprises a set  116  of micro-pulses  100  that extend from t 0  to t 5  to provide what appears to be a continuous laser emission from t 0  to t 5 . 
     It will be appreciated that the number of micro-pulses  100  and relative frequency of micro-pulses  100 , the duty cycle of micro-pulses  100 , the waveform of micro-pulses  100  and the amplitude of micro-pulses  100  illustrated in  FIGS. 6A and 6B  is for illustration purposes and may vary widely depending on the requirements for a particular laser or application. Similarly the term micro-pulses is not necessarily limiting but rather used herein to discriminate between visually apparent laser emissions that have patterns that change over time in ways that are visually apparent such the periodic laser appearance pattern  90  shown in  FIG. 5A  and micro-pulses  100  that are not visually apparent as individual pulses when emitted in patterns of more than one micro-pulse  100 . That is, in some embodiments it may be possible for a user to perceive an isolated micro-pulse  100  however, when a sequence of micro-pulses  100  is provided a user will perceive the pulse sequence as being continuous. 
     In part this occurs because, micro-pulses  100  have an amplitude, waveform, duty cycle and frequency that are defined so that when a given set of micro-pulses  100  is generated, laser  52  will emit light that appears to be continuous. In application micro-pulses  100  can have a duty cycle of about 10 to about 70 percent and a frequency from about 40 Hz to 10000 Hz depending on the characteristics of laser  52 . In other embodiments micro-pulses  100  can have a duty cycle of at least 25% to at least 60%. 
     In the embodiment that is illustrated, microcontroller  58  generates signals—either a lower voltage signal or a higher voltage signal that control operation of gate G of transistor  56 . No current flows between source S and drain D and the laser  52  emits no light when this occurs. However, when microcontroller  58  generates the higher voltage signal at gate G, current flows between source S and drain D and laser  52  emits. The actual waveform generated by laser  52  depends upon the duty cycle and frequency at which microcontroller  58  generates high voltage signals as well as characteristics of battery unit  54 , transistor  56  and other components of driver circuit  50 . 
     By using micro-pulses  100  rather than continuous draws of current from a battery unit  54 , battery unit  54  is allowed intervals of non-use during which battery unit  54  can at least partially recover from the demands of a previous micro-pulse  100  before a subsequent pulse begins. This in turn can help to ensure that battery unit  54  lasts longer and operates better using micro-pulses  100  to form an apparent laser pattern than battery unit  54  does in a continuous mode of operation. Further, in some embodiments, small capacitors  64  that occupy less than for example and without limitation one quarter or one fifth of the volume of prior art large capacitors can be used to supply a portion of the current required during micro-pulses  100 . It will be appreciated that capacitors have a rapid rate of discharge and that in some embodiments, the length of micro-pulses  100  may correspond more closely with the discharge rate of smaller capacitors  64  allowing the more effective and efficient use of such capacitors than is possible in the prior art where current is drawn for significantly longer periods of time. 
     Returning now to  FIG. 4 , after the pattern of micro-pulses  100  is determined (step  76 ) using the pattern of apparent pulses, control system  60  causes laser  52  to emit light in accordance with the determined patter of micro-pulses (step  78 ). In the embodiment of control system  60  shown above, micro-pulses  100  are generated when microcontroller  58  sets the voltage level at gate G at a high voltage level. Accordingly, in one embodiment, microcontroller  58  can act to cause emission of a continuous stream of micro-pulses  100  if a continuous apparent laser pattern is determined and alternatively can act to cause a continuous stream of micro-pulses  100  to be emitted and subsequently introduce periods where the continuous stream of micro-pulses  100  is interrupted if a periodic apparent laser pattern is determined. The periods of delay can be pre-programmed and executed at fixed timings according to a timer which may be provided in control system  60  or can be accomplished by interrupting the stream of micro-pulses  100  after a predetermined number of micro-pulses  100  has been emitted. 
     In various embodiments, any of the amplitude, waveform, duty cycle and frequency of micro-pulses  100  used in forming a continuous laser appearance pattern  92  can be different from any of the amplitude, waveform, duty cycle and frequency of the micro-pulses  100  used in forming a periodic apparent laser pattern  90 . This can be done for example, to enhance visibility, to lower power consumption, to manage heat generated by the laser emission, to utilize recovery periods provided by non-illumination periods in a periodic illumination pattern or to better match performance characteristics of laser  52  with performance characteristics of battery unit  54  for other reasons. For example, the duty cycle of micro-pulses  100  used during a periodic laser appearance pattern  90  can be up to 150% larger or smaller than that used during in a continuous laser appearance pattern  92 . 
     As is shown in  FIG. 4 , micro-pulsed laser emission to create the apparent periodic illumination continues until switch  68  opens (step  80 ). In the embodiment of  FIG. 4 , when switch  68  opens, control system  60  returns microcontroller  58  to the power down mode (step  70 ). It will be appreciated that in this way, large capacitors of the prior art can be eliminated. This enables spring guide rod laser to be made smaller, less complex and less expensive. 
       FIG. 7  illustrates another embodiment of a method for operating laser  52 . This embodiment allows a user to select from between at least two different apparent laser emission patterns from outside of a firearm having the spring guide rod laser. In this embodiment, steps  70 - 78  can be performed as described above however, this embodiment is adapted to sense when switch  68  is closed three times within a predetermined time period. Accordingly, when a first switch close is detected (step  72 ) an additional step of determining at time or setting a time based counter is performed (step  73 ). If switch  68  is then closed again (step  82 ) within a predetermined time period following step  73  and represented in this flow chart by the letter X, then control system  60  is adapted to detect whether switch  68  is closed for a second time within predetermined time period X (step  83 ), whether switch  68  is opened again within predetermined time period X (step  84 ) and whether switch  68  is closed again within predetermined time period X (step  85 ). If any of the conditions in steps  82 - 85  is not met, control system  60  determines that a first apparent laser pattern is to be used (step  74 ), determines a micro-pulse pattern to produce the first apparent laser pattern (step  76 ) and generates micro-pulses to form the first apparent laser pattern (step  78 ). However, if all three conditions are met, control system  60  determines that a second apparent laser pattern is to be used (step  86 ), determines a micro-pulse pattern to produce the second apparent laser pattern (step  87 ) and generates micro-pulses according to the determined micro-pulse pattern (step  88 ). The generation of micro-pulses continues until the switch opens again (step  89 ). 
     In this manner control system  60  enables a user to select a mode of operation based upon inputs to switch  68 . It will be appreciated that this is in part enabled by designing circuit  50  and control system  60  to allow microcontroller  58  to enter a power down mode step  70  rather than powering microcontroller  58  down at times between the opening of switch  68  and the closing of switch  68 . It will also be appreciated that there are many possible variations regarding this design, such as determining the second apparent laser pattern  98  after switch  68  has been turned on, then off, then on again. Additionally, it will be appreciated that it is possible to use this technique to select from between more than two different modes of operation based upon the number of times that switch  68  is transitioned between a closed position, an open position and back to a closed position. Further, it will be appreciated that in an alternative embodiment, it may not be necessary to determine a time but rather to use other metrics such as a number of clock cycles and a number of micro-pulses generated. 
       FIG. 8  illustrates a side cross-section view of an embodiment of a spring guide rod laser sight  40  that in this embodiment incorporates circuit  50 . As can be seen in this embodiment, spring guide rod laser sight  40  has a different architecture than that of the prior art spring guide rod laser  2 . As is shown in  FIG. 8 , in spring guide rod laser sight  40 , battery unit  54  is located within a central portion  126  of housing  122  while control system  60  is located on a first end portion  124  and laser  52  and optics  57  are located at a second end portion  128 . 
     In this embodiment battery unit  54  is electrically insulated from housing  122  in central portion  126  and a first terminal  54   a  of battery unit  54  is connected to laser  52  by way of a single connector  55  which may include as illustrated a spring  172  and intermediary board  174  and terminal  176 . Laser  52  has an electrically conductive shell  59  that is electrically connected to housing  122  which is also electrically conductive. A second terminal  54   b  of battery unit  54  is connected to control system  60  and control system  60  is in contact with housing  122  to complete control system  60 . In order to make an electrical circuit between battery unit  54  and laser  52  it is necessary for control system  60  to provide an electrical path between housing  122  and battery unit  54 . In the embodiment illustrated in  FIG. 8 , a resilient member  99  is used to provide a mechanical and electrical connection between housing  122  and a board  160  on which control system  60  is positioned. This can be done in the manner described above with transistor  56  having a drain D connected to housing  122  and a source S connected to battery unit  54  and with microcontroller  58  generating a higher voltage at a gate G of transistor  56  whenever a micro-pulse  100  is desired. In the embodiment that is illustrated in  FIG. 8 , a spring  170  is used to make electrical contact between housing  122  and control system  60  completing a return path from laser  52  without passing electrical current through any components outside of spring guide rod laser  120 . 
     In the embodiment that is shown in  FIGS. 3-8 , an electrical switch  68  is required in order to activate, deactivate laser  52  and optionally to select a laser appearance pattern. Switch  68  must be of a design that allows a user to activate it when spring guide rod laser sight  40  is installed in firearm  20 . However, switch  68  must be capable of maintaining a setting even during firing of firearm  20 , must be capable of repeated use and must be capable of allowing a setting to be made without allowing contaminants to enter housing  122 . Additionally, for the reasons discussed in greater detail above it is useful not to require components outside of housing  122  to be used as part of the electrical circuit with laser  52 . 
     Accordingly in this embodiment an original take down latch in firearm  20 , is replaced by a modified take down latch  140  and a modified take down latch spring  136 . Spring  136  biases take down latch  140  against a catch  139  of structure  141 . Take down latch  140  is generally made of metal and has a central portion bordered by at least one raised areas. When take down latch  140  is centered, a movable pin  132  is held at a position that keeps switch  68  in the open position and microcontroller  58  in the power down mode. Movement of take down latch  140  from center brings a raised portion against pin  132  advancing pin  132  into housing  122  and closing switch  68 . 
       FIG. 9  is a close up of one embodiment of a switch  68  of the present invention. As is shown in  FIG. 9 , a take down latch  140  is provided that is capable of sliding within a range of positions across a width of housing  122 . Take down latch  140  has a raised area  142  that presses pin  132  into an opening  134 . Pin  132  may move freely within an opening  134  of housing  122  to exit opening  134  as take down latch  140  is moved to different positions across the width of housing  122 . As this occurs, pin  130  drives a movable first contact  150  of switch  68  that is electrically connected to housing  122  from a position that is not in contact with a second contact  152  on board  160  as is shown in  FIG. 9  to a position where first contact  150  is in electrical contact with second contact  152  as shown in  FIG. 10 . This closes switch  68  and creates an electrical path between microcontroller  58  and ground bringing microcontroller  58  out of the power down mode. Such movement can be against a bias provided by a biasing member such as a spring. 
       FIGS. 11 and 12  illustrate another embodiment of switch  68 . In this embodiment, switch  68  is operated in the same manner—in response to a sliding action of take down latch. However in this embodiment, a first contact  150  of switch  68  is in a fixed position relative to housing  122  and second contact  152  is in a fixed position relative to board  160 . In this embodiment, board  160  is slidably movable along a length of housing  122  and pin  132  engages a contact member  162  on board  160  to move board  160  from a first position shown in  FIG. 11  where a second contact  152  mounted to board  160  does not contact first contact  150  to a second position shown in  FIG. 12  where second contact  152  is brought into contact with first contact  150 . Such movement can be against a bias provided by a biasing member such as a spring  164 . Other embodiments are possible, for example, in one embodiment either of first contact  150  or second contact  152  can be joined to pin  130 . Additionally, it will be appreciated that the system can be made to work in the converse with switch  68  closing when pin  132  is fully extended from housing  122  and opening when pin  132  is pressed further into housing  122 . 
       FIGS. 13 and 14  illustrate another embodiment of the invention. In this embodiment, a micro switch  155  is provided to perform the function of switch  68  of  FIG. 3  and is positioned so that movement of pin  132  causes micro switch  155  to change state. In this embodiment, micro switch  155  has a biasing member  157  such as a spring that drives micro switch plunger  156  and conductor  153  an open position shown in this embodiment as a position where a conductor  153  is separated from first contact  150  and second contact  152 . However, when the bias is overcome by force transmitted during movement of pin  132  caused in turn by movement of take down latch  140  as shown in  FIG. 13B , conductor  153  provides a conductive path between first contact  150  and second contact  152 . Other types of known micro switches can be used for micro switch  155 . 
       FIGS. 15A, 15B, 15C, 15D, 15E and 15F  illustrate top views of various examples of the many different types of raised areas  142  that can be used on a take down latch  140  to engage a pin  132 . As is shown in  FIGS. 15A and 15B  two raised areas  142  are provided having arcurate shape allowing take down latch  140  such that pin  132  is depressed or released continuously as take down latch  140  is moved across width W of housing  122 . 
     As is shown in  FIGS. 15C and 14D  raised areas  142  can include a sloped engagement surface  142 A and a flat  142 B that is reached when pin  132  has reached a predetermined extent of movement into housing  122 . It will be appreciated that providing raised areas  142  that are shown in  FIGS. 15A, 15B, 15C and 15D , allows bi-lateral activation of switch  68  in that they allow take down latch  140  to be moved in two directions across width W while achieving the same effect on pin  132 . This advantageously allows a take down latch  140  to be moved across a width from a right side or from a left side of housing  122  in order to control the state of switch  68 . However, this bi-directional capability is not necessary and as is shown in  FIGS. 15E and 15F  take down latch  140  can have a sloped raised area  142  that is arranged for movement in one direction only. 
     It will be appreciated that in the embodiments described above, opening  134  in housing  122  is, at all times, substantially occupied by pin  132 . This works to prevent contaminants from the firearm discharge process, from firearm cleaning or other maintenance and from the environment in general from entering into housing  122  through opening  134  while allowing pin  132  to enter into and exit from housing  122 . Further, it will be appreciated that the entire electrical path from laser  52  to control system  60  and battery unit  54  is within housing  122  thus preventing such contaminants from interposing themselves in the electrical path thereby further extending battery life as can occur when electrical paths outside of housing  122  are used. 
       FIG. 16  illustrates another embodiment of a driver circuit  50  for a spring guide rod laser sight  40 . In this embodiment, driver circuit  50  has the same arrangement of functional components as described in the embodiment shown above, however, it also has a second transistor  200  that is arranged in combination with transistor  56  to provide reverse battery protection. In this regard drain D of transistor  56  is connected to drain D of second transistor  200 , Gate G of transistor  56  and gate G of second transistor  200  are connected together, source S of transistor  56  is connected ground, and source S of second transistor  200  is connected between laser  52  and diode  62  so that if the battery unit  54  is connected backward, current cannot flow in an inverse direction to laser  52 . 
       FIGS. 17A and 17B  illustrate yet another embodiment in which take down latch  140  is biased by one or more biasing members into a centered position. That is unless a user actively presses against take down latch  140  against the bias, take down latch  140  will be biased to a centered position. In this embodiment two biasing members  220  and  222  are shown in the form of springs, however, other knowing resilient structures or substances can be used. In this embodiment, microcontroller  58  detects temporary transitions of switch  68  and reacts to these as a start of a new steady state condition and treats a subsequent temporary transition as an end of the steady state condition. That is rather than requiring that take down latch  140  be physically moved to a position that depresses pin  132  and held in this position while laser  52  is active, microcontroller  58  can sense a temporary depression of pin  132  and respond to the temporary depression as if the depression was maintained until the next temporary depression of pin  132 . 
     Accordingly, for example, in the embodiment of  FIG. 7 , microcontroller  58  utilizing this approach to perform the method of  FIG. 7 , could interpret a first detected transition as a switch close (step  72 ), a second transition as a switch open (step  80 ), a third transition as a second switch close (step  83 ), a fourth transition as a second switch open (step  84 ), and a fifth transition as a third switch close (step  85 ). If all of these events occurred within time X of the first transition then the second apparent laser pattern would be used as is generally described above. 
     This approach advantageously allows “tap on/tap off” operation of spring guide rod laser sight  40  which does not rely on mechanical positioning of take down latch  140  to maintain a desired state of operation. 
     It will be appreciated that the spring guide rod laser sight  40  described herein offers any or all of a compact, efficient, externally adjustable and reliable laser design that can be uses as a spring guide rod in a firearm. It will also be appreciated that this is not limiting and that spring guide rod laser sight  40  be applied in other circumstances where a compact, efficient, externally adjustable or reliable laser is desired.