Abstract:
A digital depth gauge apparatus is provided for measuring a depth of a hole in, or surface of, an object using a variable-resistance sensor. The apparatus comprises an elongated reader body that includes a distal end and a proximal end having a longitudinal axis and a user interface including a display and at least one actuator that controls operation of at least one of the display and the apparatus. The apparatus includes a probe that extends from the distal end of the reader body, the probe including a tip for locating a distal surface of the object. The reader body proximal end is configured to abut an other surface of the object. An electrical resistance-based sensor is provided to determine an extension distance of the probe from the body.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Application No. 61/096,524, filed Sep. 12, 2008, entitled, “ELECTRONIC DEPTH GAUGE WITH VARIABLE ELECTRICAL RESISTANCE SENSING”, herein incorporated by reference. 
     The present application also contains subject matter related to U.S. patent application Ser. No. 12/391,814, filed Feb. 24, 2009, U.S. patent application Ser. No. 11/376,399, filed Mar. 15, 2006, and U.S. Pat. No. 7,165,336, the entire content of these being herein incorporated by reference. 
     BACKGROUND 
     The present invention relates generally to measuring instruments. More particularly, the invention pertains to an apparatus for determining a distance relative to changes in a variable electrical resistance, and an electronic depth gauge including the apparatus. 
     Various measuring devices are known for determining the distance between two points. Such measuring devices employ a variety of mechanical, electromechanical, and/or electrical/electronic techniques for sensing or determining relative or absolute distances. For example, gauges with graduated scales, magnetic or optical encoders, ultrasonic, infrared, and capacitive or inductive measuring devices are all known. However, an electronic depth gauge as described herein using a variable electrical resistance to measure distance would be advantageous. 
     SUMMARY 
     Accordingly, a digital depth gauge apparatus is provided for measuring a depth of a hole in, or surface of, an object, the apparatus comprising: an elongated reader body that includes a distal end and a proximal end having a longitudinal axis; a user interface including a display and at least one actuator that controls operation of at least one of the display and the apparatus; a probe that extends from the distal end of the reader body, the probe including a tip for locating a distal surface of the object; the reader body proximal end configured to abut an other surface of the object; and an electrical resistance-based sensor fixedly positioned relative to at least one of: a) the reader body, and b) the probe, and movably positioned relative to, respectively, at least one of: b) the probe, and a) the reader body, the sensor comprising an interface to the user interface display and having an output indicating a relative distance between the probe tip and the proximal end of the reader body. 
     The apparatus may further comprise a slider element that is one of actuators, the slider element being attached to the probe and movable in a direction parallel to the longitudinal axis of the body; wherein the sensor comprises a linear variable resistor element and a conducting element that contacts the linear variable resistor element at some point along its length, the slider element being fixedly attached to at least one of the conducting element and the linear variable resistor element to effect relevant motion between the two as the slider is moved; the apparatus further comprising: a power source attached across the variable resistor element at a fixed voltage or current; and circuitry to measure voltage or current within the variable resistor element that is related to a position of the conducting element along the linear variable resistor element; and circuitry to convert and display the variable resistor element voltage or current as a distance related to a distance between the probe tip and the proximal end of the reader body. 
     The variable resistor element may comprise two parallel resistive strips arranged on the circuit board. The slider element may comprise: a base portion; and a coupling portion, the coupling portion holding the conducting element so that the conducting element creates an electrical contact between the two parallel resistive strips at a particular location. The coupling portion may protrude through a slit on the printed circuit board. The resistive strips may comprise a series of discrete bands, each having a predetermined resistance. 
     The body may be a sealed body, and the sealed body may comprise: a first seal that is located at the proximal end of the body and seals a location of the body through which the probe extends; and a second seal that is located along a slider opening and seals a location of the body through which the slider extends. The first seal may be a generally disk-shaped seal, and the second seal may be a seal extending longitudinally along the body between the body case and the printed circuit board, and comprises a slit through which a portion of the slider extends. 
     The apparatus may be holdable and operable with a single hand, and the total length of the body may be between 150 mm and 250 mm. The apparatus may further comprise an ergonomic treatment located on an exterior surface of the body, and the ergonomic treatment may be formed from a thermoplastic elastomer. The apparatus may be self-contained and comprises its own power source. 
     Advantages of variable resistance technology include increased accuracy and durability in the surgical field by mitigating interference caused by the presence of fluid and soft tissue. The technology is cost effective when used as a single use device and unlike optical, magnetic, infrared, conductive, inductive, or ultrasonic devices, there is no interference with other technology present in the surgical suite. The use of variable resistance technology permits development of a very small and ergonomically advantageous device for users in an environment such as the operating room. 
     The biggest advantages of VR technology is the size particularly as it relates to inductive technology. Specifically VR technology allows us to create a small ergonomically advantageous device necessary for success in the operating room. Optical, ultrasonic, and infrared technologies are as accurate, but have more difficulty in such an implementation due to the impedance caused by the body as well as other machinery in the operating room; importantly, such devices are also very expensive to use when a disposable device is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following describes the drawings that illustrate various embodiments of the invention. 
         FIG. 1A  is a perspective view of an embodiment of an electronic depth gauge; 
         FIG. 1B  is a partially-exploded perspective view of the electronic depth gauge of  FIG. 1 ; 
         FIG. 2A  is a partially-exploded top perspective view of internal components of the electronic depth gauge of  FIG. 1 ; 
         FIG. 2B  is a partially-exploded bottom perspective view of internal components of the electronic depth gauge of  FIG. 1 ; 
         FIG. 2C  is a simplified circuit diagram illustrating the variable resistor component; 
         FIG. 3A  is a side view of an exemplary probe of the electronic depth gauge of  FIG. 1 ; 
         FIG. 3B  is a side detail view of the tip portion of the probe shown in  FIG. 3A ; 
         FIG. 4A  is a side view of an exemplary top housing portion of the electronic depth gauge of  FIG. 1 ; 
         FIG. 4B  is a bottom perspective view of the top housing portion of the electronic depth gauge of  FIG. 1 ; 
         FIG. 4C  is a top perspective view of the top housing portion of the electronic depth gauge of  FIG. 1 ; 
         FIG. 5A  is a top view of the bottom housing portion of the electronic depth gage of  FIG. 1 ; 
         FIG. 5B  is a top perspective view of the bottom housing portion of the electronic depth gage of  FIG. 1 ; 
         FIG. 5C  is a bottom perspective view of the bottom housing portion of the electronic depth gage of  FIG. 1 ; 
         FIG. 6  is a perspective view of an exemplary sliding carriage of the electronic depth gauge of  FIG. 1 ; 
         FIGS. 7A-B  are top and bottom perspective views of an exemplary seal of the electronic depth gauge of  FIG. 1 ; 
         FIGS. 8A-B  are top and bottom views of an exemplary printed circuit board of the electronic depth gauge of  FIG. 1 ; and 
         FIGS. 9A-B  are parts of an exemplary electrical circuit schematic of the electronic depth gauge of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discusses various embodiments of the invention. The Figures illustrate embodiments of a variable electrical resistance apparatus for measuring a distance, and an electronic depth gauge including the same are provided. 
     Referring to  FIG. 1A , an exemplary electronic depth gauge  100  is shown. The gauge  100  includes a generally elongated housing  120 , an electronic display  140  and one or more actuators (e.g., an on/off/measurement-hold button  160  and a slider  180  as shown). As shown in  FIG. 1B , the gauge  100  further includes a probe  200  that telescopes into and out from the housing to measure a distance between two points.  FIG. 1B  further shows that housing  120  may be formed of two complementary-formed parts  122 ,  122 ′ that may be mated, engaged, connected or otherwise coupled together (e.g., snap-fit, glued, welded, fastened using screws, etc.). 
     Although the gauge  100  may be used in the context of measuring the depth or length of a hole in a bone (e.g., during an orthopedic, oral maxillofacial, etc. surgery), it should be appreciated that the gauge  100  may be used for various applications where it is desired to measure a distance between two points. 
     In one exemplary use of the illustrated gauge  100 , a surgeon drills a hole (e.g., a pilot hole) in a bone and inserts the gauge  100  into the surgical field to measure the depth of the hole for selecting a fastener (e.g., screw, bolt, pin, wire, etc.) that will be inserted into the hole to fasten bones or pieces of bones together. Once a distal end of the gauge  100  is placed or aligned with the hole, the user (e.g., the surgeon) then moves the slider  180  distally (as indicated in  FIG. 1A  by arrow “D”) to extend the probe  200  (shown in FIGS.  1 B and  3 A-B) through the hole. 
     After the surgeon determines that the probe  200  has exited a distal end of the hole, the surgeon moves the slider  180  proximally (as indicated in  FIG. 1A  by arrow “P”) so that an engagement surface (e.g., barb, catch, etc.) at the distal end of the probe  200  may find purchase on the distal surface of the bone. The surgeon may move the slider  180  further in the proximal direction after the probe  200  has achieved purchase so that the distal end of the housing  120  rests against the proximal surface of the bone. In this way, a depth of the hole is measured or otherwise determined according to a length of the probe that is extended or projected from the distal end of the housing  120 . The length is then displayed on display  140 . The surgeon may press the on/off/hold button  160  to freeze the display  140  and/or store the displayed value in a memory for recall after the gauge  100  has been removed from the surgical field. The gage could also be used where the hole is not a through-hole, and thus the gauge could serve to operate as a simple depth gage with the tip end contacting a bottom surface of the hole. 
     Referring now to  FIGS. 2A and 2B , various internal components of the example electronic depth gauge  100  shown in  FIG. 1  are described. As shown in  FIG. 2A , the gauge  100  includes a first seal  110 , a circuit board  130 , a carriage  150 , a second seal  170 , and a power source  190 . The seals are preferably made of biocompatible rubber polymers. The first seal  110  is configured at the distal end of the housing. The first seal  110  is generally annular or toroidal in shape so that the gauge&#39;s probe  200  ( FIG. 1B ) can extend or otherwise project through the first seal  110  while preventing intrusion of contaminants (e.g., liquid such as bodily fluid, or solids such as dust, dirt, etc.) into the housing  120 . The housing  120  is preferably of a length that makes it holdable and operable with one hand, e.g., in a range of 150-250 mm, however, other lengths could clearly be used. 
     The gauge  100  further includes a circuit board  130  to which components of the gauge  100  are electrically and/or physically coupled. The circuit board  130  may be a printed circuit board, that is, a rigid substrate with conductive traces on one or both sides thereof. As shown, the circuit board  130  is generally elongated along a longitudinal axis defining a center of the gauge  100 , and the display  140  is mounted to a distal end of the circuit board  130 . Although the display  140  illustrated in  FIGS. 1A-2B  shows numeric digits, it should be appreciated that the display  140  may be configured otherwise to show, for example fewer or additional indicia (e.g., alphanumeric characters), symbols, etc. As shown in  FIG. 9A , one embodiment of the display may be configured to show three alphanumeric characters. 
     As can be appreciated from  FIGS. 2A and 2B , the carriage  150  couples with the slider  180  so that the carriage  150  may be moved proximally and distally by the user along a portion of the circuit board  130 , particularly the slot  132  shown in  FIGS. 2A ,  2 B. As will be discussed in further detail hereinafter with reference to  FIG. 6 , the carriage  150  includes a base portion  152  and a coupling portion  154 . The base portion  152  of the carriage  150  is configured on a bottom surface of the circuit board  130 , and the coupling portion  154  extends upward from the base portion  152  and through the slot  132  in the circuit board  130  to couple with the slider  180  for moving the base portion  152  along the semiconductive trace or traces  134 A, B. As shown in  FIG. 2B , a conductive member  136  is configured on the coupling portion  154  of the carriage  150  between the base portion of the carriage  150  and the bottom surface of the circuit board  130  for contacting and bridging across the semiconductive traces  134 A, B ( FIG. 2B ). By moving the conductive member  136  along the traces, a different effective length through which electrical current flows is achieved, which can then be accurately measured as a current (for a constant voltage source), or as a voltage (for a constant current source). 
       FIG. 2C  illustrates a simplified circuit diagram of the variable resistor VR, where X represents the distance of movement, with V O  being the voltage. As the distance X increases, so will V O , and, based on a software calibration, this circuit creates a measurement value based on a minimum and maximum value that is calibrated into the software. 
     In the preferred embodiment, the conductive member  136  is isolated, i.e., not attached to any other point of the circuit except where it creates a conductive path between the two semiconductive traces  134 A, B. However, it is also possible to provide an electrical connection (e.g., a flexible wire or thin cable) between the conductive member  136  and other parts of the circuitry as well. 
     The semiconductive traces  134 A, B may be formed from carbon, carbon compound, or other suitable semiconductor material, and the traces  134 A, B may be configured as continuous members or as a series of discrete bands (e.g., each band having a predetermined resistance). Furthermore, linear (preferable) or logarithmic tapers could be used. These semiconductive traces  134 A, B are joined by conductive traces  138  located on either side. When carbon printing on a PCB is used, a line accuracy for the gage is approximately 1%, and the display  140  may be configured to display to an accuracy of, e.g., 0.1 mm. To achieve accurate carbon placement, in order to place the carbon traces on the PCB, a specialized printer may be used that deposits the material in a linear manner along the length of the board. 
     Calibration may be mediated by the variable resistance tracing artwork relative to the PCB artwork. Both pieces of information may be scanned into the printing software which then uses a microprocessor to align the two images to ensure printing occurs along the predetermined pathway. Then, the device software is loaded onto the microprocessor which subsequently sets a zero point for the carbon traces and a maximal point by extending the probe relative to precise gauge blocks. This is performed by the gauge manufacturer and follows a software standard operating procedure, ensure accuracy. 
     As can be appreciated, the conductive member  136  and semiconductive traces  134 A,  134 B define a linear potentiometer with the conductive member  136  functioning as the wiper for varying or changing a resistance relative to a position of the conductive member  136  (and a position of the slider  180 ) along the length of the traces  134 A,  134 B. Since the probe  200  moves relative to the slider  180 , a distance that the probe  200  is extended from the housing  120  can be determined based on the resistance of the linear potentiometer—for example, according to a measured voltage (resulting from a constant current flowing though the variable resistance), or a measured current (resulting from a constant voltage across the variable resistance). 
     In an alternate embodiment, the semiconductive traces could also be associated/affixed to structure associated with the probe  200 , with the conductive member being affixed at some point on the PCB  130 , so that movement of the probe  200  still results in relative motion between the semiconductive traces and the conductive member serving as a center tap, wiper, or electrical conductor for the potentiometer. 
     As shown in  FIG. 2A , the second seal  170  is configured with a longitudinal slot or aperture therein which corresponds to a longitudinal slot  132  ( FIG. 2B ) or aperture in the circuit board  130 . The second seal  170  is configured on the top surface of the circuit board  130  such that the coupling portion of the carriage  150  extends through the second seal  170  to couple with the slider  180 . The second seal  180  is configured to prevent intrusion of contaminants (e.g., liquid such as bodily fluid, or solids such as dust, dirt, etc.) into the housing  120  through one or more apertures thereof (e.g., a first aperture defined in the housing  120  through which button  160  extends, and an elongated aperture or slot defined in the housing  120  and along which the slider  180  moves). 
     As further shown in  FIGS. 2A and 2B , the power source  190  may be one or more disposable or rechargeable batteries, which may be permanently installed or removable/replaceable. Alternatively, the gauge  100  may include a jack, interface, or cord to connect the gauge  100  to a source of power such as a typical 120/240 volt AC receptacle. 
     Referring now to  FIGS. 3A , B, an exemplary probe for the gauge  100  is described. As shown, the exemplary probe  200  includes a central portion  210 , a proximal portion  220  and a distal portion  230  with an engagement surface  240 .  FIG. 3A  illustrates a side elevation view of the exemplary probe  200 , and  FIG. 3B  is a detail view of the distal end and probe tip  240 . 
     As shown, the distal portion  230  may have a diameter that tapers or otherwise decreases from the central portion  210  toward the engagement surface  240 . As can be appreciated from  FIG. 3B , the distal portion  230  may be curved or angled relative to the central portion  210 . Preferably, the probe  200  has a length that permits it to be fully retracted into the body  120 . In an exemplary embodiment in which the body is between 150 mm and 250 mm in length, then the probe would have just a slightly shorter length to fit within the body. Although various dimensions have been discussed for the illustrated example probe, indeed, the probe may be configured otherwise. The probe  200  may be designed to protrude somewhat even in a fully retracted position. The probe may be completely straight (i.e., the distal portion  230  being coaxial and coextensive with the central portion  210 ) instead of including a curved portion. 
     Referring now to  FIGS. 4A-C , a top portion of the housing  120  ( FIG. 1 ) is described. Although various configurations are shown for the illustrated top housing portion, it may be configured otherwise.  FIG. 4A  is a side view of the top housing portion  122 .  FIG. 4B  is an interior perspective view of the top housing portion  122 .  FIG. 4C  is an exterior perspective view of the top housing portion  122 . 
     As shown in  FIGS. 4A-C , hereinafter collectively referred to as  FIG. 4 , the top housing portion  122  includes a first portion  123  and a second portion  128 . The first portion  123  is generally rectangular in shape for retaining the circuit board  130  ( FIGS. 2A-B ) and other internal components of the gauge  100 . As shown, first portion  123  includes a first aperture  124 , a second aperture  126  and a third aperture  127 . The first aperture  124  is configured as a generally elongated slot or slit in the top housing portion  122  so that the coupling portion of carriage  150  ( FIGS. 2A-B ) can extend therethrough and move laterally therealong. The second aperture  126  is configured as a generally circular hole through which the button  160  extends. The third aperture  127  is configured as a generally rectangular window for viewing the display  140  ( FIGS. 1A and 2A ). 
     As shown in  FIG. 4 , the first portion  123  may include or bear thereon a graduated scale  125  configured alongside the first aperture  124 . Although the graduated scale  125  is shown relative to the gauge  100 , other embodiments of the gauge need not include a graduated scale. A user of the gauge  100  may read a point on the graduated scale  125  corresponding to a center (e.g., a center ridge) of the slider  180  ( FIGS. 1A and 2A ) to determine (or independently verify/double-check the value being displayed on the display  140 ) a depth or length of an object that is being measured. The graduated scale  125  may be configured in one or more units of measurement, for example English and/or metric units. 
     As shown in  FIG. 4 , the first portion  123  may include a first chamber  121  and a second chamber  129 . As shown, the first chamber  121  is configured at a proximal end of the first portion  123  for retaining the power source  190  ( FIGS. 2A-B ). The second chamber  129  is configured at a distal end of the first portion  123  for retaining the first seal  110  ( FIGS. 2A-B ). The probe  200  ( FIGS. 3A-B ) extends from the carriage  150  ( FIGS. 2A-B ), which is configured to move proximally and distally in the first portion  123  relative to movement of the slider  180 , and through the second portion  128  to extend from and retract into the distal-most end of the second portion  128 . 
     Referring now to  FIGS. 5A-C , a bottom portion  122 ′ of the housing  120  ( FIG. 1 ) is described. Although various dimensions are shown for the illustrated bottom housing portion, indeed, it may be configured otherwise.  FIG. 5A  illustrates an interior plan view of the bottom housing portion  122 ′.  FIG. 5B  is a plan view of the bottom housing portion  122 ′.  FIG. 5C  is an exterior perspective view of the bottom housing portion  122 ′. As can be appreciated from  FIGS. 5A-C , hereinafter collectively referred to as  FIG. 5 , the bottom housing portion  122 ′ is configured to mate with the top housing portion  122  ( FIG. 4 ) to define the housing  120 , thereby sealing and protecting the internal components. As shown in  FIG. 5 , the bottom housing portion  122 ′ is configured with ledges to support and hold the circuit board  130  ( FIGS. 2A-B ) and other internal components of the gauge  100 . 
     As shown in  FIG. 5 , the bottom housing portion  122 ′ may be formed with an ergonomic treatment to facilitate positive gripping of the gauge  100  and/or prevent or reduce fatigue of the user&#39;s hand during use of the gauge  100 . As shown, the ergonomic treatment may be a plurality raised ridges  124 ′. The ergonomic treatment may be formed of a suitable (e.g., grip-enhancing, silicone-like, spongy, etc.) material such as a thermoplastic elastomer. As can be appreciated, the bottom housing portion  122 ′ may be formed in two parts—a first part is a formed part having the raised ridges  124 ′ and a contoured surface designed to mate with a bottom plastic portion, with the ridges  124 ′ configured to protrude through holes in the second part that is attached, connected or otherwise coupled with the first part. In one example, the bottom housing portion  122 ′ may be formed by injection molding process where the second part is overmolded onto the first part. 
     Turning now to  FIG. 6A , the carriage  150  ( FIGS. 2A-B ) will be described in further detail. Although various aspects are shown for the illustrated carriage, indeed, it may be configured otherwise (e.g., relative to the housing portions  122 ,  122 ′).  FIG. 6  is a perspective view of the carriage  150 . As shown in  FIG. 6 , the carriage  150  includes a base portion  152  and a coupling portion  154  that extends or projects from a top surface of the base portion  152 . 
     As is best shown in  FIGS. 2A and 2B , the coupling portion  154  is configured to mate with the slider  180  for moving the conductive member  136  along the traces  134 A,  134 B on the bottom surface of the circuit board  130 . To this end, the base portion  152  of the carriage  150  further includes projections  156  at the distal and proximal ends thereof for maintaining the curved or arced shape of the conductive member  136 . As further shown in  FIG. 6 , the base portion  152  of the carriage  150  further includes an aperture  158  (e.g., a blind hole) into which the probe  200  (particularly the proximal end  220  of probe  200 ) is inserted and/or coupled. In some embodiments the probe  200  may be removable from the carriage  150  for various reasons including, but not limited to, facilitating cleaning/sterilization of the gauge  100 . 
     Turning now to  FIGS. 7A-B , the second seal  170  ( FIGS. 2A-B ) will be described in further detail. Although various aspects are shown for the illustrated second seal, indeed, it may be configured otherwise (e.g., relative to the configuration of the circuit board  130  and/or housing portions  122 ,  122 ′).  FIG. 7A  illustrates a top perspective view of the second seal  170 , and  FIG. 7B  illustrates a bottom perspective view of the second seal  170 . As shown in  FIGS. 7A-B , hereinafter collectively referred to as  FIG. 7 , the second seal  170  includes a lengthwise-extending slit  172 , and an aperture  174 . As can be appreciated, the slit  172  is configured to be complementary with the elongated slot  132  of the circuit board  130 . The slit  172  may function as a self-sealing closure that allows movement of the coupling portion  152  of the carriage  150 , but prevents contaminants from contacting the circuit board  130  that is below the seal  170 . 
     Furthermore, the aperture  174  is configured to accommodate the button  160  ( FIGS. 1A and 2A ) so that liquid or solid contaminants do not enter the housing  120  and contact the circuit board  130  when the user presses the button (e.g., to turn the gauge  100  on or off, or to hold or store a length/depth measurement). 
     Turning now to  FIGS. 8A-B , the circuit board  130  ( FIGS. 2A-B ) will be described in further detail. As shown in  FIG. 8A , the top side or surface of the circuit board  130  includes various wires or traces for electrically connecting previously-described components including, for example the power source  190  ( FIGS. 2A-B ), the display  140 , and the switch  160  ( FIGS. 1A and 2A ). A bullseye-shaped wiring trace  137  shown in  FIG. 8A  corresponds with the switch  160 , and the traces at the proximal end (i.e., the right-hand side as shown in  FIG. 8A ) marked with “+” and “−” correspond with the power source  190 . Slot  132  extends along a centerline of the board  130  longitudinally between the bullseye-shaped trace and the +/−traces. At a distal end (i.e., the left-hand side as shown in  FIG. 8A ), traces marked with “LCD” interface the display  140  ( FIGS. 1A and 2A ) with a controller or processor (shown in  FIG. 8B  and  FIGS. 9A , B). As shown in  FIG. 8B  the bottom side or surface of the circuit board  130  includes various wires or traces for electrically connecting a controller or processor  138  with previously-described components including, for example, the linear potentiometer (defined by the semiconductive traces  134 A,  134 B and the conductive member  136 ), the power source  190  ( FIGS. 2A-B ), the display  140 , and the switch  160  ( FIGS. 1A and 2A ). 
     Turning now to  FIGS. 9A , B (collectively,  FIG. 9 ), an exemplary circuit schematic is described for the gauge  100 . As shown in  FIG. 9 , the circuit  300  includes a controller or processor  310 , such as that disclosed in document by Microchip® PIC16F913/914/916/917/946 Data Sheet: 28/40/44/64-Pin Flash-Based 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology, 2007 (Document No. DS41250F), herein incorporated by reference (PIC16/F913 shown in  FIG. 9 ), an LCD display screen  140 , a switch  330 , a variable resistor (e.g., 100KΩ (1%) surface mount device), and an optional in-circuit serial programming (ICSP) interface  350 . The controller or processor  310  is in electrical communication with the display  140  for controlling or driving the display  140  to indicate a length or depth measurement relative to the variable resistor  340 . The controller or processor  310  may be any suitable microprocessor, microcontroller, digital signal processor (DSP), field programmable gate array (FPGA), application specific integrated circuit (ASIC) or the like. 
     The display screen  140  as shown is an LCD panel for displaying three alphanumeric characters as well as the indicia “hold” and a unit of measurement (e.g., “mm” as shown). Although the illustrated LCD panel  140  is configured to show three alphanumeric characters, it may be configured otherwise to display fewer or additional characters or indicia. Furthermore, the display screen  140  may be other types of displays known in the art such as a light-emitting diode display and the like. 
     The switch  330  may be a microswitch, snap dome or the like that couples with button  160  ( FIG. 1A ) for turning the gauge  100  on and off. Furthermore, the controller  310  may include a timer and be programmed with a power save mode—that is instructions for turning off the gauge  100  after a predetermined amount of time. Additionally, the switch  330  when pressed and held for a predetermined period of time may signal the controller  310  to freeze the display  140  and/or to store the measurement displayed thereon to a memory for recall at a later time. In some embodiments, the user may actuate the switch  330  to change units of measurement (e.g., English to metric and vice versa). Although the variable resistor  340  may be defined by the semiconductive traces  134 A,  134 B and conductive member  136  (best illustrated in  FIG. 2   b ), it should be appreciated that other types of linear potentiometers, which relate electrical resistance and linear displacement, may be employed in the present electronic depth gauge. Furthermore, a rotary potentiometer could also be used if a mechanism is provided for converting linear motion to rotary motion. Such a mechanism could include, e.g., one or more circular and linear gears in combination. 
     The software modules used in the controller may be stored as program instructions or computer readable codes executable on the processor on a computer-readable media such as read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. This media can be read by the computer, stored in the memory, and executed by the processor. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     For the purposes of promoting an understanding of the principles of the invention, reference has been made to the preferred embodiments illustrated in the drawings, and specific language has been used to describe these embodiments. However, no limitation of the scope of the invention is intended by this specific language, and the invention should be construed to encompass all embodiments that would normally occur to one of ordinary skill in the art. 
     The present invention may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions. For example, the present invention may employ various integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, and the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. Similarly, where the elements of the present invention are implemented using software programming or software elements the invention may be implemented with any programming or scripting language such as C, C++, Java, assembler, or the like, with the various algorithms being implemented with any combination of data structures, objects, processes, routines or other programming elements. Furthermore, the present invention could employ any number of conventional techniques for electronics configuration, signal processing and/or control, data processing and the like. The words “mechanism” and “element” are used broadly and are not limited to mechanical or physical embodiments, but can include software routines in conjunction with processors, etc. 
     The particular implementations shown and described herein are illustrative examples of the invention and are not intended to otherwise limit the scope of the invention in any way. For the sake of brevity, conventional electronics, control systems, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent exemplary functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. Moreover, no item or component is essential to the practice of the invention unless the element is specifically described as “essential” or “critical”. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural. Furthermore, recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Finally, the steps of all methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. Numerous modifications and adaptations will be readily apparent to those skilled in this art without departing from the spirit and scope of the present invention. 
     TABLE OF REFERENCE CHARACTERS 
     
         
           100  electronic depth gage 
           110  first seal 
           120  generally elongated housing 
           120 P housing proximal end 
           120 D housing distal end 
           121  first chamber of first portion 
           122  top housing part 
           122 ′ bottom housing part 
           123  first portion of top housing part 
           123 ′ bottom housing 
           124  first aperture of first portion 
           124 ′ grip portion 
           125  graduated scale 
           126  second aperture of first portion 
           127  third aperture of first portion 
           128  second portion of top housing part 
           129  second chamber of first portion 
           130  circuit board 
           132  Slot 
           134 A, B semiconductive traces 
           136  conductive member 
           137  button contact conducting member/bullseye wiring trace 
           138  conductive traces 
           140  electronic display 
           150  Carriage 
           152  carriage base portion 
           154  carriage coupling portion 
           158  carriage aperture 
           160  on/off/measurement-hold button 
           170  second seal 
           180 , 180 ′ Slider 
           190  power source 
           200  Probe 
           210  central portion of probe 
           220  proximal portion of probe 
           230  distal portion of probe 
           240  engagement surface, probe tip 
           300  Circuit 
           310  controller/processor 
           320  Display 
           330  Switch 
           340  variable resistor (possibly implemented as  134 A,  134 B,  1   
           350  programming interface