Abstract:
An obscured feature detector operates from a stationary position on a surface being examined. The detector includes a plurality of sensor plates positioned in an array on the underside of the device, which sense the examined surface. The sensor plates are connected to a capacitance sensing circuit, which connects to indicators positioned on the back side of the detector through additional circuitry. A handle positioned on the back of the detector allows the user to grasp the device and place it in a stationary position on the surface being examined while also observing the indicators on the back side of the detector. Increases in capacitance caused by the presence of features behind or within the surface being examined are detected by the sensor plates and the capacitance sensing circuit. The indicators identify locations of larger capacitances, associated with the presence of a feature, such as a stud, beam, or electrical wiring.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the following patent applications: U.S. Provisional Patent Application No. 61/339,316, entitled “MATERIAL DETECTOR THAT OPERATES FROM A STATIONARY POSITION” and filed on Mar. 4, 2010; U.S. Provisional Patent Application No. 61/333,252, entitled “MATERIAL DETECTOR THAT OPERATES FROM A STATIONARY POSITION” and filed on May 10, 2010; U.S. Provisional Patent Application No. 61/345,591, entitled “MATERIAL DETECTOR THAT OPERATES FROM A STATIONARY POSITION” and filed on May 17, 2010. The entire contents of these patent applications are incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to devices used for detecting the presence of obscured features behind opaque, solid surfaces, more specifically, devices used for locating beams and studs behind walls and joists beneath floors. 
     2. Background 
     The need to locate obscured features such as beams, studs, joists and other support elements behind walls and beneath floors is a common problem encountered during construction, repair and home improvement activities. Often a need exists to cut or drill into a supported surface with the aim of creating an opening in the surface while avoiding the underlying support elements. In these instances, it is desirable to know where the support elements are positioned before beginning so as to avoid cutting or drilling into them. On other occasions, one may desire to anchor a heavy object to the obscured support element. In these cases, it is often desirable to install a fastener through the surface in alignment with the underlying support element. However, once the wall, floor or surface is in place, the location of the support element is not visually detectable. 
     A variety of rudimentary techniques have been employed with limited success to address this problem in the past. These have included driving small pilot nails through the surface until a support element is detected and then covering over holes in the surface that did not reveal the location of the stud or support. A less destructive technique comprises tapping on the surface in question with the aim of detecting audible changes in the sound which emanates from the surface when there is a support element beneath or behind the area being tapped. This technique is not very effective, however, because the accuracy of the results depend greatly on the judgment and skill of the person searching for the support, and because the sound emitted by the tapping is heavily influenced by the type and density of the surface being examined. 
     Magnetic detectors have also been employed to find obscured support elements with the detector relying on the presence of metallic fasteners, such as nails or screws, in the wall and support element to trigger a response in the detector. However, since metallic fasteners are spaced at discreet locations along the length of a support, a magnetic detector may pass over a length of the support where no fasteners are located, thereby failing to detect the presence of the obscured support element. 
     Capacitive displacement sensors have also been employed to detect obscured features behind opaque surfaces. These detectors sense changes in capacitance on the examined surface that result from the presence of features positioned behind, beneath or within the surface. These changes in capacitance are detectable through a variety of surfaces such as wood, sheet-rock, plaster, gypsum and do not rely on the presence of metal fasteners in the surface or obscured feature for activation of the sensor. 
     However, conventional capacitive sensors often suffer from a number of shortcomings. For example, conventional capacitive sensors typically require movement across an examined surface, sometimes repeatedly, to effectively locate an obscured feature or support element. In addition, capacitive sensors generally can only locate one feature at a time, and often can only find the edge of the feature rather than its center point. Some capacitive sensors rely on an assumed width of a feature to calculate the location of the center of the feature based on detection of the edge. Such devices frequently require a comparison circuit in addition to a sensing circuit in order to compare capacitances sensed by different sensors. 
     SUMMARY 
     The present disclosure advantageously addresses one or more of the aforementioned deficiencies in the field of obscured feature detection by providing an accurate, simple to use and inexpensively manufactured obscured feature detector. The detector can be employed by placing the device in a stationary position against the examined surface and reading the location of all features present beneath the surface where the device is positioned without having to move it back and forth across the surface. 
     In one embodiment, an obscured feature detector comprises a plurality of sensor plates, each having a capacitance that varies based on: (a) the proximity of the sensor plate to one or more surrounding objects; and (b) the dielectric constant(s) of the surrounding object(s). The obscured feature detector further comprises a sensing circuit coupled to the sensor plates and a controller coupled to the sensing circuit. The sensing circuit is configured to measure the capacitances of the sensor plates, and the controller is configured to analyze the capacitances measured by the sensing circuit to identify sensor plates located in one or more regions of relative high capacitance, as well as sensor plates located in one or more regions of relative low capacitance. The obscured feature detector further comprises a plurality of indicators coupled to the controller, each indicator capable of toggling between a deactivated state and an activated state. The controller is configured to activate one or more of the indicators to identify the location of region(s) of relative high capacitance. 
     In another embodiment, a stationary obscured feature detector comprises a housing having a top, a bottom, and an interior cavity, with a handle located near the top. The housing is configured to be placed against a surface at a first location to detect the presence of one or more features obscured by the surface near the first location, without requiring movement of the stationary obscured feature detector. The stationary obscured feature detector further comprises a plurality of sensor plates arrayed substantially in a plane near the bottom of the housing. Each sensor plate has a capacitance that varies based on: (a) the proximity of the sensor plate to one or more surrounding objects; and (b) the dielectric constant(s) of the surrounding object(s). The stationary obscured feature detector further comprises a sensing circuit located in the interior cavity of the housing and coupled to the sensor plates, a controller located in the interior cavity of the housing and coupled to the sensing circuit, and a plurality of indicators located near the top of the housing and coupled to the controller. The sensing circuit is configured to transmit charge to the sensor plates and read the capacitances of the sensor plates. The controller is configured to analyze the capacitances measured by the sensing circuit and control the indicators to identify the location of the feature(s) obscured by the surface near the first location. 
     In another embodiment, a method of detecting an obscured feature behind a surface comprises placing an obscured feature detector in a stationary position on the surface. The obscured feature detector has a plurality of sensor plates arranged in an array. The method further comprises measuring capacitance readings sensed in a plurality of regions, each region corresponding to an area surrounding one or more of the sensor plates, and comparing the sensed capacitance readings in different regions. The method further comprises identifying, based on the compared capacitance readings, one or more regions of relative high capacitance, and activating one or more indicators corresponding to the location of the region(s) of relative high capacitance. 
     In some embodiments, the obscured feature detector comprises at least four sensor plates. In some embodiments, the obscured feature detector comprises a housing having a longitudinal axis with a length of at least about 6″. In some embodiments, a dedicated sensing circuit is connected to each sensor plate. 
     In some embodiments, sensor plates are electrically connected together in groups of two or more in order to improve signal to noise ratio without the loss of detection resolution that would result from the use of wider plates. In some embodiments, comparative measurements are made between individual sensor plates, or various groups of sensor plates. 
     In some embodiments, one or more non-active sensor plates can be left at a high impedance floating potential. This may result in increased sensitivity for some combinations of groups of active sensor plates. 
     In some embodiments, the indicators are arrayed along one of the edges of the housing parallel with a longitudinal axis of the housing. In some embodiments, the ratio of indicators to sensor plates is other than 1:1. In some embodiments, the indicators do not change states while the capacitance sensing circuit is active, in order to minimize interference with the sensing operation. 
     In some embodiments, the obscured feature detector may simultaneously locate and indicate the presence of more than one feature beneath an examined surface. 
     In some embodiments, the obscured feature detector includes a re-chargeable battery or a fuel cell. 
     In some embodiments, the obscured feature detector is at least 16″ long so that it immediately detects at least one support when placed in a stationary and horizontal orientation against a wall in a modern US home where support studs are spaced at 16″ intervals from center to center. 
     A novel and non-obvious feature of the obscured feature detector and associated method is the ability to locate obscured features without having to move the detector across the examined surface. The obscured feature detector may be used by placing it in a stationary position on the surface to be examined. This obviates the need to slide the obscured feature detector back and forth along the surface in order to detect a feature, thereby allowing a user to better observe and mark the position of the feature. 
     Another novel and non-obvious feature of the obscured feature detector is the ability to simultaneously locate more than one obscured feature positioned beneath the detector. 
     Another novel and non-obvious feature is the use of only one capacitance-to-digital converter to sense a plurality of sensor plates, or groups of sensor plates, individually and sequentially. This technique is in contrast with the more common approach of using a separate capacitance-detecting circuit for each sensor plate. 
     Another novel and non-obvious feature is the detection of supports by the use of absolute changes in capacitance in each individual sensor plate instead of ratiometric comparisons between adjacent plates. As a result, the obscured feature detector can advantageously sense and indicate the location of features of various shapes and/or widths. 
     Still another novel and non-obvious feature of the obscured feature detector is the ability to indicate the presence of obscured features anywhere along the length of the obscured feature detector instead of just at the center-point of the detector. 
     The present disclosure will now be described more fully with reference to the accompanying drawings, which are intended to be read in conjunction with both this summary, the detailed description, and any preferred or particular embodiments specifically discussed or otherwise disclosed. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of illustration only so that this disclosure will be thorough, and fully convey the full scope of the invention to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a perspective view of a first embodiment of an obscured feature detector. 
         FIG. 1B  illustrates a perspective view of a second embodiment of an obscured feature detector. 
         FIG. 2  is a perspective view of a sensor plate array suitable for use with an obscured feature detector. 
         FIG. 3  is a block diagram of certain functional components of an obscured feature detector. 
         FIG. 4  is a block diagram of a controller suitable for use with an obscured feature detector. 
         FIG. 5  is a cross sectional view of an obscured feature detector with a block diagram of a charging and sensing circuit projected on the cross-section. 
         FIG. 6  is a cross sectional view of an obscured feature detector while in use on an examined surface having an obscured feature. 
         FIG. 7  illustrates the response of the indicators of an obscured feature detector to the increased capacitance caused by the detection of an obscured feature. 
         FIG. 8  is a flow diagram showing a feature detection process implemented in some embodiments of an obscured feature detector. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that modifications to the various disclosed embodiments may be made, and other embodiments may be utilized, without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
     To provide context for the disclosure it may be useful to understand how capacitance is used to detect obscured features behind a surface. Capacitance is an electrical measure of an object&#39;s ability to hold or store charge. A common form of an energy storage device is the parallel plate capacitor whose capacitance is calculated by: C=∈r ∈o A/d, where A is the overlapping area of the parallel plates, d is the distance between the plates and ∈r is the relative static permittivity, or dielectric constant of the material between the plates. ∈o is a constant. The dielectric constant (∈r) of air is one, while most solid non-conductive materials have a dielectric constant greater than one. Generally, the increased dielectric constants of non-conductive solids enable conventional capacitive displacement sensors to work. 
     In their most rudimentary form, capacitive sensors are in part single-plate capacitive sensors. These single-plate capacitive sensors use the environment surrounding them as the dielectric where the second plate can be assumed to be infinitely far away. The plates will also form capacitors with other metal plates. When two plates are positioned against a wall, they are not facing each other as is suggested by the definition of a capacitor. Nonetheless, the stray fields emanating from the edges of each of the adjacent plates do extend into the wall and behind it, and curve back to the adjacent plate, allowing the two plates to sense the capacitance of the surface and the space behind the surface. 
     When the plates are placed on a wall at a location with no support behind the wall, the detector measures the capacitance of the wall and the air behind it. When placed in a position having a support behind the wall, the detector then measures the capacitance of the wall and the support, which has a higher dielectric constant than air. As a consequence, the detector registers an increase in capacitance which can then be used to trigger an indicating system. 
     This description of feature sensing through capacitive sensing is provided in order to facilitate an understanding of the disclosure. Persons of skill in the art will appreciate that the scope and nature of the disclosure is not limited by the description provided. 
     The present disclosure is directed to an obscured feature detector. In the exemplary embodiments illustrated in  FIGS. 1-7 , the obscured feature detector  10  comprises a sensor plate array  31  (see  FIG. 2 ), a multi-layer printed circuit board  40  (see  FIG. 5 ), a charging and sensing circuit  30  (see  FIG. 3 ), a controller  60  (see  FIGS. 3-5 ), a display circuit  50  (see  FIG. 3 ), a plurality of indicators  52  (see  FIGS. 1 ,  3 ,  5 ), a power controller  20  (see  FIG. 3 ) and a housing  12  (see  FIGS. 1 ,  5 ). 
     In some embodiments, as shown in  FIG. 2 , the sensor plate array  31  comprises a plurality of sensor plates  32  arranged in a planar array. Each sensor plate  32  has a capacitance that varies based on: (a) the proximity of the sensor plate  32  to one or more surrounding objects, and (b) the dielectric constant(s) of the surrounding object(s). Thus, by evaluating the capacitances of the sensor plates  32 , the sensor plate array  31  is capable of sensing the presence and location of one or more features  82  obscured by a surface  80  (see  FIG. 6 ) in contact or proximity with the obscured feature detector  10 . 
     The sensor plates  32  may be positioned side by side in a linear arrangement so that a longitudinal axis of the array  31  is substantially perpendicular to a longitudinal axis of the individual sensor plates  32 . The individual plates  32  may comprise thin, conductive surfaces and may be manufactured using a variety of suitable techniques, such as, for example, depositing conductive ink on a substrate  34  or applying thin sheets of conductive material to the substrate  34 . 
     In some embodiments, each individual sensor plate  32  of the array  31  is independently connected to the charging and sensing circuit  30  (see  FIG. 3 ), and the array  31  itself is attached to the exposed side of the bottom layer  41  of the printed circuit board  40  which is positioned facing the underside of the detector  10  (see  FIG. 5 ). In some embodiments, the obscured feature detector  10  has at least four sensor plates  32 , which advantageously enables the obscured feature detector  10  to detect the full width of a common obscured feature  82 , such as a stud, from a stationary position. By contrast, many existing stud detectors with fewer than four sensor plates cannot detect the full width of a stud without being moved. 
     In some embodiments, as shown in  FIG. 5 , the printed circuit board  40  comprises a multi-layer board with a bottom layer comprising a sensor board  41  on which the sensor plate array  31  is placed, two middle layers comprising a power plane board  42  and a ground plane board  43  respectively, and a top layer comprising a metal shielding board  44 . In other embodiments the sensor plate array  31  may be placed on a middle layer of the printed circuit board  40  to provide an insulating layer to protect the circuits from static discharge. Placing the sensor plates  32  on a middle layer may have the added benefit of minimizing the expansions and contractions of the sensor plates  32  as the printed circuit board  40  is flexed. 
     In some embodiments, the printed circuit board  40  may be external to the material detector housing  12  and the circuits are only protected by the external layer, or layers, of the printed circuit board  40 . The printed circuit board  40  may be made from a variety of suitable materials, such as, for example, FR-4, FR-406, or more advanced materials used in radio frequency circuits, such as Rogers 4003C. Rogers 4003C may offer improved temperature stability. In the embodiment illustrated in  FIG. 5 , the printed circuit board  40  is positioned inside the housing  12  with the sensor board  41  containing the sensor plate array  31  oriented toward the underside of the obscured feature detector  10  and the shielding board  44  positioned as the top layer of the printed circuit board  40  immediately beneath the housing  12 . 
     In some embodiments, as shown in  FIG. 3 , the charging and sensing circuit  30  comprises a plurality of electrical traces  35 , a multiplexer  37 , and a capacitance-to-digital converter  38 . The charging and sensing circuit  30  may be connected to the controller  60 . In some embodiments, each of the electrical traces  35  between the controller  60  and the sensor plates  32  have substantially the same length and width. As a result, the traces  35  have substantially similar electrical properties (resistance, capacitance, and inductance) and substantially similar response to environmental conditions, such as temperature. The electrical traces  35  may comprise conductive paths on the printed circuit board  40 , which connect the individual sensor plates  32  to the input port of the controller  60 . As a result, the sensor plates  32  may be individually connected to the charging and sensing circuit  30 . 
     In some embodiments, as shown in  FIG. 4 , the controller  60  comprises a processor  61 , a clock  62 , a random access memory (RAM)  64 , and a non-volatile memory  65 , In operation, the controller  60  receives programmable code  66  and synchronizes the functions of the charging and sensing circuit  30  with the display circuit  50  (see  FIG. 3 ). The clock  62 , which may be integrated into the controller  60 , times and switches the connection of the individual sensor plates  32  to the charging and sensing circuit  30 . The non-volatile memory  65  receives and holds the programmable code  66  as well as look-up tables (LUT) and calibration tables  68 . The programmable code  66  may include number of suitable algorithms, such as, for example, an initialization algorithm, a calibration algorithm, a base-lining algorithm, a charging and sensing algorithm, a proximal sensor zeroing algorithm, a multiplexing algorithm, a display management algorithm, an active sensor activation algorithm, and a non-active sensor management algorithm. 
     In some embodiments, as shown in  FIG. 3 , the display circuit  50  comprises a plurality of shift registers  54  and a plurality of indicators  52 . The shift registers  54  may be connected in series between the controller  60  and the indicators  52 . In operation, the shift registers  54  may transmit state change signals generated by the controller  60  to an indicator  52  corresponding to a sensor plate  32  that detects a capacitance level indicating the presence of a feature  82  (see  FIG. 6 ), such as a stud or support. The indicators  52  may comprise LEDs, LCD displays, incandescent bulbs, or other suitable indicators. In the embodiments illustrated in  FIGS. 1A and 1B , the indicators  52  are positioned in receptacles  18  in the backside of the housing  12  in one or more linear arrays, with each individual indicator  52  aligned with a corresponding sensor plate  32  to which the indicator  52  is connected through the display circuit  50 . 
     In some embodiments, as shown in  FIGS. 1A and 1B , the housing  12  comprises an upper housing  13 , a lower housing  14 , an on/off switch  24 , a handle  15 , a plurality of receptacles  18  and a power supply compartment  16 . The upper housing  13  may contain the multi-layered printed circuit board  40 , the charging and sensing circuit  30 , the display circuit  50 , and the controller  60  in an interior cavity. In some embodiments, the housing  12  may be made of a variety of dielectric materials, including but not limited to ABS plastic, PVC, acetal, or nylon. The lower housing  14  may comprise a thin dielectric plate that mates with the upper housing  13  and covers the downward-facing sensor plate array  31  to protect it from damage. The lower housing  14  may be fastened to the upper housing  13  using a variety of suitable techniques, such as, for example, screws or a snap mechanism. 
     In some embodiments, the handle  15  comprises a gripping surface positioned orthogonally from the back plane of the upper housing  13 . The handle  15  is preferably positioned so that the user&#39;s hand does not obscure the view of the indicators  52  when grasping the handle  15 . In some embodiments, the power supply compartment  16  comprises a cavity for holding a suitable power supply, such as batteries or a fuel cell, and a cover for accessing the compartment  16 . 
     In some embodiments, as shown in  FIG. 3 , the obscured feature detector  10  comprises a power controller  20  having a power source  22 , an on-off switch  24 , and a voltage regulator  26 . The power source  22  may comprise an energy source for charging the sensor plates  32 , powering the indicators  52 , and supplying power to the capacitance charging and sensing circuit  30 , the controller  60  and the display circuit  50 . In some embodiments, the power source  22  may comprise a DC battery supply or an AC adapted power supply. The on-off switch  24  may be used to activate the sensor plate array  31  and other components of the obscured feature detector  10  when it is placed on or near a surface  80 , as described above. In some embodiments, the on-off switch  24  comprises a push button mechanism that activates components of the obscured feature detector  10  for a selected time period. In some embodiments the on-off switch  24  comprises a capacitive sensor that may sense the presence of a finger, or thumb over the button. In some embodiments, the on-off switch  24  may comprise a toggle switch, or other types of buttons or switches. The voltage regulator  26  may be used to condition the output of the power controller  20 , as desired. 
     In operation, the charging and sensing circuit  30  may implement a capacitance-to-digital conversion process. As an initial step, the obscured feature detector  10  can be placed in a stationary position against a surface  80  to be examined and activated using the on-off switch  24 , as described above. The charging and sensing circuit  30  may then individually charge a first sensor plate  32  of the obscured feature detector  10 . In subsequent iterations of the capacitance-to-digital conversion process, additional sensor plates  32  in the sensor plate array  31  can be charged sequentially by the charging and sensing circuit  30 . In some embodiments, to maintain appropriate levels of sensitivity, non-active sensor plates  32  (e.g., those not connected to the charging and sensing circuit  30  at any given moment), are positively controlled by a suitable method, such as allowing them to float in a high-impedance state, driving them to ground potential, or driving them to the same potential as the shielding board  44  of the multi-layer PCB  40 . 
     Once a first sensor plate  32  has been charged, the charging and sensing circuit  30  allows the charged sensor plate  32  to share the charge with a modulation capacitor, which may be connected to the sensor plate  32  in series through a modulation resistor. The voltage of the modulation capacitor can then be measured and compared against a reference voltage. The charge sharing process is repeated iteratively until the voltage on the modulation capacitor reaches the reference voltage. In some embodiments, the controller  60  counts the number of iterations that occur before the modulation capacitor reaches the reference voltage. This count indicates the capacitance of the sensor plate  32 , with lower counts corresponding to greater capacitances. Once the capacitance of the first sensor plate  32  has been determined, the capacitance-to-digital conversion process can be repeated sequentially for the remaining sensor plates  32  to determine their respective capacitances. 
       FIG. 8  is a flow diagram showing a feature detection process  200  implemented in some embodiments of the obscured feature detector  10 . The detection process  200  begins with a first step  202 , in which the obscured feature detector  10  is initialized and/or calibrated. In some embodiments, initialization occurs automatically after the obscured feature detector  10  is turned on. Calibration can advantageously compensate for differences in the sensor plates  32 , such as differences in dielectric constant, plate size and trace length, all of which can have an effect on the accuracy of the readings. In some embodiments, a two-dimensional calibration table  68  is applied to the sensor plates  32 , which enables them to produce similar readings in response to similar capacitive loads. In some embodiments, the two-dimensional calibration table  68  compensates for temperature variations and may provide separate temperature calibration depending on the sensed capacitive load. 
     Referring again to  FIG. 8 , in a next step  204 , the capacitance of each sensor plate  32  is measured individually. In a next step  206 , the controller  60  sorts the measured capacitance readings in ascending or descending order to determine the relative capacitance values of the individual sensor plates  32 . In a step  208 , the controller  60  analyzes the sorted capacitance values of the sensor plates  32  to identify one or more regions of relative high capacitance and relative low capacitance in the area of the sensor plates  32 . In some embodiments, the controller determines an appropriate threshold value, or baseline, indicating the presence of a possible obscured feature  82 . This process, sometimes referred to as base-lining, can “teach” the obscured feature detector  10  what the capacitive load of the examined surface  80  is, so it can factor out that load when evaluating signals. For example, in some embodiments, the controller  60  may select the third lowest capacitance measurement as the threshold, or baseline, value. 
     In a step  210 , the calibrated capacitance of the sensor plate  32  with the highest capacitance reading is compared against the selected threshold value. In a decision step  212 , a determination is made as to whether this highest calibrated capacitance reading exceeds the threshold value. If not, processing returns to step  204 , and the intervening steps are repeated until at least one sensor plate  32  reaches a calibrated capacitance reading that exceeds the selected threshold value. Once the results of decision step  212  indicate that the maximum capacitance reading exceeds the threshold, then in a step  214 , the charging and sensing circuit  30  performs additional capacitance readings of the sensor plates  32  near the one reporting the highest capacitance. These additional measurements advantageously enable the obscured feature detector  10  to determine the location of the feature  82  more precisely. In a next step  216 , the appropriate indicators  52  are illuminated to indicate the location of the obscured feature  82  to the user. For example, in some embodiments, the controller  60  transmits a signal through the shift registers  54  of the display circuit  50  to activate the indicators  52  that correspond to the sensor plates  32  registering capacitance values that indicate the presence of the obscured feature  82 . 
     In some embodiments, the differences in capacitance readings between adjacent regions are compared to identify the boundaries between high capacitance regions and low capacitance regions. Once the boundaries between high capacitance regions and low capacitance regions are identified, then indicators are illuminated over the high capacitance regions. 
     In some embodiments, the capacitance readings are compared to pre-identified patterns to identify the location of obscured features  82 . In one example of one particular pattern, a region of three high capacitance readings surrounded by low capacitance readings is used to identify the location of a single object about one and half inches wide, that may correspond to a stud. In another example of a particular pattern, a region of six high capacitance readings surrounded by low capacitance regions is used to identify the location of an object about three inches wide, that may correspond to the location of two studs located side by side. 
     In some embodiments, algorithms use triangulation to locate one or more obscured features  82 . In such embodiments, an assumption is typically made that the distance to an object is inversely proportional to the capacitance reading. Using this assumption, the location of an obscured feature  82  can be determined by using a triangle with the known location of two sensor plates  32  and the inverse of the capacitance readings as the vertices of the triangle. 
     In other embodiments, different algorithms are utilized that use capacitance readings in other ways to identify the location of obscured features  82 . In some embodiments, various combinations of different algorithms are utilized to identify the location of obscured features  82 . 
     Referring again to  FIG. 8 , in a next step  218 , the illuminated indicators  52  are eliminated from the list of available display elements. In a step  220 , the controller  60  decrements the capacitance readings of sensor plates  32  adjacent to those indicating the presence of the obscured feature  82 . These decrementing adjustments are made to reduce the possibility of a “false positive” indication of an additional obscured feature  82 . In some cases, sensor plates  32  that are near, but not over, an obscured feature  82  will signal an increase in capacitance greater than the selected threshold value. Thus, if no decrementing adjustment is made, the controller  60  may misinterpret those readings as being indicative of an additional obscured feature  82 . 
     Once the decrementing adjustments are made in step  220 , processing returns to step  210 , at which the obscured feature detector  10  checks for additional obscured features  82  by comparing the highest remaining capacitance measurement against the selected threshold value. The process steps described above are repeated, except that sensor plates  32  already acknowledged by the controller  60  as having detected an obscured feature  82  are not evaluated again. In some embodiments, to minimize electrical noise during the capacitance sensing, the controller  60  does not change the state of the indicators  52  while the charging and sensing circuit  30  is active. 
     In some embodiments, to improve the signal to noise ratio, adjacent sensor plates  32  may be electrically connected in groups of two, three or more plates in a rolling sweep, thereby effectively increasing the plate size without increasing the overall size of the obscured feature detector  10 . For example, in some embodiments, the first, second and third sensor plates  32  may be grouped together and read as one, followed by the second, third and fourth sensor plates  32  being grouped together and read as one, and so on. This grouping can be accomplished by connecting multiple sensor plates to the capacitance to digital converter  38  using the multiplexer  37 . 
     Another technique for reducing signal to noise ratio is to read the sensor plates  32  in groups of one, two, three, or more. The groups of sensor plates  32  sampled may be adjacent during some scans, and not adjacent during others. For example, in some embodiments, the second sensor plate  32  is sensed individually, followed by the first, second and third sensor plates  32  being grouped together and sensed as a unit. These two readings are then combined by the controller  60  before adjusting the state of the associated indicators  52 . 
     In some embodiments, differential detection is employed, whereby one group of sensor plates  32  is compared to an alternate group of sensor plates  32 . The groups of compared sensor plates  32  may, or may not, be adjacent. Each group of compared sensor plates  32  may comprise one or more sensor plates  32 . Many combinations are possible. Those skilled in the art can determine which of the many combinations are most suitable for a desired design. Combining the readings from a variety of different combinations of readings, including both differential and non-differential readings, can provide composite readings that can detect more deeply, with more accuracy, and less noise. 
     In one particular example, the obscured feature detector  10  comprises nineteen sensor plates  32  arrayed side by side in vertical orientation along the longitudinal axis of the detector  10 , with a gap of approximately 1.7 mm between adjacent plates. In this particular example, each sensor plate  32  has a width of about 11 mm wide and a length of about 45 mm. The sensor plates  32  may be manufactured of conductive ink deposited onto the bottom surface  41  of a multi-layer printed circuit board  40 . The multi-layered printed circuit board  40  may be selected from a material used to manufacture RF printed circuit boards in order to resist dielectric constant variance and dimensional variances associated with temperature variations. 
     The capacitance to digital conversion process may be accomplished by the AD7147 from Analog Devices. Other controllers that may be used to perform the capacitance to digital conversion include the AD7477 from Analog Devices, the PsoC controller CY8C21534 from Cypress Semiconductor, the C8051CF706 from Silicon Laboratories, or others. 
     The display circuit  50  functions may be performed using the MM74HC164 shift registers from Fairchild Semiconductor. This display circuit  50  transmits a signal from the controller  60  to the indicators  52 , which may comprise LEDs arrayed along the back of the upper housing  13  in two parallel rows, with two opposing indicators on either side of the back of the housing corresponding to each of the nineteen sensor plates  32  for a total of 38 indicators  52 . The power controller  20  may comprise the MC33375 integrated circuit from On Semi. 
     The housing  12  may be manufactured from ABS plastic. In order to accommodate the nineteen sensor plates  32 , the housing  12  may have a length of about 10″ and a width of about 3″. A handle  15  running along the longitudinal axis of the upper housing  13  can be designed to be easy to hold while keeping the user&#39;s hand about 1″ away from the surface of the PCB  40  and at the same time not obscuring the user&#39;s line of sight to the rows of indicators  52  positioned on the back side of the upper housing  13 . In other embodiments, the user&#39;s hand may be less than 1″ away from the surface of the PCB  40 . 
     In some embodiments, the housing  12  has a longitudinal axis with a length of at least about 6″, which advantageously enables the obscured feature detector  10  to span the full width of a common obscured feature  82 , such as a stud, from a stationary position. By contrast, many existing stud detectors are not wide enough to span the full width of a stud without being moved. 
     In other embodiments, the obscured feature detector  10  may be longer than 16″, with about thirty sensor plates  32 . Such a configuration may be particularly advantageous, because many structures built according to standard construction methods in the United States have studs spaced 16″ apart on center. Thus, whenever an obscured feature detector  10  having a length greater than about 16″ is placed against a wall of such a structure, the detector  10  will typically indicate the presence of at least one stud on the first try. 
     In some embodiments, the obscured feature detector  10  can be operated in different modes. For example, the user may select a first mode suitable for detecting materials with a dielectric constant between about 2 and 6 corresponding to non-conductive construction materials such as wood, or a second mode suitable for detecting conductive construction materials such as metal studs. 
     In some embodiments, the obscured feature detector  10  has an alternate operating mode that can be selected to search only for the region with the highest capacitance. An algorithm that always displays the highest reading independent of the signal strength may be able to find hidden objects that would be considered noise level in normal mode. 
     In some embodiments, the obscured feature detector  10  has a flexible printed circuit board  40  that allows the printed circuit board  40  to bend to match the contour of the surface  80  to be detected. In these embodiments, one or more printed circuit boards  40  are flexibly connected to the housing  12  using a medium such as foam rubber, springs, gel, hinges, pivot points, an encapsulated gas such as air, a housing body having flexible features, or other suitable compressible or flexible media. 
     In some embodiments, the obscured feature detector  10  uses a plurality of printed circuit boards  40  that may each be flexibly connected to the detector housing  12 . 
     In some embodiments, the housing  12  has flexible features that allow the housing  12  to flex or bend to adapt to the contour of a non-flat detecting surface. In one particular example, an obscured feature detector  10  uses two printed circuit boards  40 . Each printed circuit board  40  is attached to the housing  12 . In this particular example, the housing  12  is able to flex in the center, such that each sensor plate  32  more closely matches the contour of the surface  80  to be detected. In some embodiments, the housing  12  is mostly or entirely flexible. 
     In some embodiments, an auto-calibration adjustment mode is provided. The auto-calibration adjustment mode records and stores the capacitive readings from each of the regions. It compares the readings from substantially adjacent regions and determines if one particular sensor plate  32 , or region, tends to have higher or lower readings than its adjacent sensor plate(s)  32  or region(s). When a pattern is detected that one particular sensor plate  32  or one particular region consistently has substantially higher or lower readings than adjacent sensor plates  32  or regions, then adjustments are made to the calibration table to remove the abnormality. 
     In some embodiments, the obscured feature detector  10  can be operated in a first mode suitable for detecting obscured features  82  through a thin surface that may correspond to a thin piece of sheet rock, or a second mode suitable for detecting obscured features  82  through a thick surface that may correspond to a thick piece of sheetrock. 
     In some embodiments, the obscured feature detector  10  can be operated in a first mode suitable for detecting obscured features  82  behind a first surface material with a comparatively higher dielectric constant such as a OSB or plywood, or a second mode suitable for detecting obscured features  82  behind another surface material with a lower dielectric constant such as gypsum sheetrock. 
     In some embodiments, the obscured feature detector  10  can be operated in a first mode suitable for detecting an obscured feature  82  that is embedded within a material, such as detecting a pipe within concrete, or a second mode suitable for detecting when the obscured feature  82  is located on the other side of a surface  80 , such as detecting a stud on the other side of a piece of sheetrock. 
     Although the present disclosure is described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art, given the benefit of this disclosure, including embodiments that do not provide all of the benefits and features set forth herein, which are also within the scope of this disclosure. It is to be understood that other embodiments may be utilized, without departing from the spirit and scope of the present disclosure.