Patent Publication Number: US-2018039351-A1

Title: Methods and apparatus for metal touch sensor

Description:
TECHNICAL FIELD 
     This application relates in general to touch sensors, and in particular to metal touch sensor devices. 
     BACKGROUND 
     Touch sensors continue to replace mechanical devices such as buttons and switches as user inputs into electronic appliances. Example applications include consumer goods such as kitchen and laundry appliances, electronic door controls, and fan and AC controls, as well as industrial applications. 
     Capacitive touch sensors are often used. In one form of capacitive touch sensing, a single sensor acts as one plate of a variable capacitance. When a user&#39;s finger approaches the sensor, the user&#39;s finger acts as a second plate and a capacitance value can be detected corresponding to a touch. A non-conductive overlay will typically cover the sensors and protect the sensors. In an alternative arrangement, capacitors are formed of two plates placed in proximity and energized. When a user&#39;s finger approaches the sensor, the user&#39;s finger changes the electric field and the change can be detected. 
     Capacitive touch sensors with non-conductive overlays cannot sense a gloved touch. In many industrial and outdoor applications, the user may be wearing gloves. Capacitive touch sensors cannot operate properly when wet or when water is present. The sensors are susceptible to noise commonly found in AC powered systems. Covering a typical capacitive touch sensor with a protective metal layer renders the system inoperative. 
     Co-owned U.S. Pat. No. 8,624,871, entitled “Method and apparatus for sensing and scanning a capacitive touch panel,” naming Nihei et. al. as inventors, describes the use of capacitive touch panels with sensing electronics. 
     SUMMARY 
     In described examples, an apparatus includes a metal plate having a plurality of defined areas forming touch sensors on a first planar surface, and having an opposing planar surface. The metal plate is arranged to be deformable in the plurality of defined areas by a human touch, and the metal plate has non-touch areas in areas other than the defined areas. A circuit board has a plurality of conductive sensors on a first surface arranged with the plurality of conductive sensors facing and spaced from the opposing planar surface of the metal plate, the conductive sensors placed in correspondence with the defined areas on the metal plate so that deflection sensors are formed in the defined areas by the conductive sensors and the opposing planar surface of the metal plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a capacitor having two plates. 
         FIGS. 2A-2B  are a diagram of a metal touch sensor detecting a deflection in a touch sensor using capacitive sensing, and an equivalent circuit diagram, respectively. 
         FIG. 3  illustrates a conventional metal touch sensor assembly using capacitive sensing. 
         FIG. 4  is a plan view of a first planar surface of a metal plate for a touch sensor having defined touch areas. 
         FIG. 5  shows in a projection of an opposing planar surface of a metal plate of an embodiment. 
         FIG. 6  shows in a projection a metal touch sensor embodiment incorporating the metal plate of  FIG. 5 . 
         FIG. 7  shows in a projection another embodiment for a metal touch sensor assembly. 
         FIG. 8  shows in another projection an alternative embodiment for a metal touch sensor. 
         FIG. 9  shows in a projection of an alternative metal touch sensor embodiment. 
         FIG. 10  illustrates in a circuit block diagram a processor coupled to a metal touch sensor. 
         FIG. 11  is a flow chart for a method embodiment. 
         FIG. 12  shows in a projection another metal touch sensor embodiment. 
         FIG. 13  shows in a projection the opposing planar surface of a metal plate for use in a metal touch sensor embodiment. 
         FIG. 14  shows in a projection the opposing planar surface of a metal plate for use in an alternative metal touch sensor embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     The figures are not necessarily drawn to scale. The term “coupled” may include connections made with intervening elements, and additional elements and various connections may exist between any elements that are described as “coupled.” 
       FIG. 1  illustrates in a cross sectional view a plate capacitor  100 . In  FIG. 1 , capacitor  100  has an upper plate  101 , which can be a metal conductive plate, and a lower plate  103  spaced from the upper plate. The plates  101 ,  103  have an overlapping surface area A. In the example of  FIG. 1 , an air dielectric  105  separates the upper and lower plates, although in alternative  arrangements other dielectric materials are used. The upper and lower plates are spaced from one another by a distance “d”. 
     The capacitance of the capacitor  100  is given in Farads by Equation 1: 
         C     r     o*A/d    (1)
 
     Without describing in detail the units and dielectric constants  r and  o, it is clear the capacitance in Farads is inversely proportional to the distance d between the plates. A change in distance d therefore changes the capacitance. The metal touch sensor takes advantage of this change in distance to detect a touch. 
       FIGS. 2A-2B  illustrate a metal touch sensor and a corresponding equivalent circuit schematic. In  FIG. 2A , a sensor  200  includes a conductive metal plate  201  having a first planar surface for receiving a touch and opposing planar surface on an opposite side, a circuit board PCB  209 , a sensor pad  203  on a first surface of the circuit board  209 . A spacer  207  keeps the opposing surface of the metal plate  201  at a predetermined distance from a circuit board  209 . The circuit board  209  carries sensors  203  on a first surface. The sensors can be of copper, and may be a copper foil or copper electroplated layer that is patterned. In an example, the area of sensor  203  is larger than the end of a human finger and it may be around 100 mm 2 . The opening in the spacer  207  can be larger than the sensor area. A larger opening in spacer  207  can enable a larger deflection in the metal plate. 
     The metal plate has to be of a thickness that allows a deflection due to a human touch. As shown in  FIG. 2A , when the pressure of a human finger is applied to the metal plate  201 , it deflects and a change in capacitance proportional to the change in the distance “d” can be detected. By application of a sensing voltage to the bottom plate of the capacitor, which is the sensor  203 , a capacitance value can be obtained. By repeatedly scanning a plurality of sensors, a system can detect changes in capacitance and thereby detect a touch. The sensors  203  detect deflections in the metal plate  201  caused by a finger or stylus moving the metal plate  201  towards the sensor  203 . The capacitive sensors  203  therefore form deflection sensors. 
     The spacer  207  must be rigid. Deflections in areas between the designated touch areas can result in false touch detections. A movement in the metal plate in a touch area that is away from the area actually being touched can also cause a false touch detection. The spacer must be adhered to the metal plate  201  to prevent adjacent areas of the metal plate  201  that are away from the touch from deflecting while a designated touch area is deflected. 
       FIG. 3  illustrates in a projection view a conventional metal touch sensor  300 . In  FIG. 3 , some components are similar to those of  FIG. 2  and for those components, similar reference labels are used, for clarity. For example, the metal plate  201  corresponds to metal plate  301  in FIG. 3 . In  FIG. 3 , a first planar surface  302  of a metal plate  301  forms an exterior of the touch sensor. Spacer  307  is beneath an opposing planar surface of metal plate  301  (not visible in the projection of  FIG. 3 ) and a circuit board  309  is d beneath spacer  307 . Sensors  303  on the circuit board  309  are positioned facing and in corresponding to the defined touch areas  311  on the first planar surface of metal plate  301 . The circuit board  309  and sensors  303  are spaced from the opposite planar surface of metal plate  301  by the spacer  307 . 
     The “buttons”  311  on the first planar surface  302  of metal plate  301  are not physically separate from the rest of the first planar surface of the metal plate  301 , but instead are designated areas for sensing touch. The designated areas  311  can be indicated by decals, paint, screen-printing, etching or dyes to color the metal differently from the surrounding non-touch areas. Other visual cues can be used to indicate where the defined touch areas are. Sensors  303  form a bottom plate of capacitors with the opposite planar surface (not visible in  FIG. 3 ) of metal plate  301  forming the top plate in the designated touch areas. The sensors  303  and the opposing surface of metal plate  301  form deflection sensors. A deflection in a designated touch area  311  can be detected due to a change in capacitance at one of the sensors  303 . Sensing circuitry (not shown in  FIG. 3 ) that can include analog to digital converters, analog front ends, and digital processors, can determine when a particular sensor changes capacitance, and by determining which one of the sensors changed capacitance, a touch can be identified. Scanning of the sensors can be used to continuously check for a deflection in the metal plate  301 . 
     Conventional touch sensors such as  300  in  FIG. 3  have several problems that need to be improved. A touch in a non-touch area can deflect the metal plate enough so that the proximate sensors such as  303  in  FIG. 3  can erroneously detect a deflection, indicating a touch. The erroneous deflection results in a false touch detection, and can lead to a false data entry. The spacer  307  adds costs and materials and the spacer materials can become detached from the metal plate  301 , causing additional deflections in the areas not being touched. A metal touch sensor that does not detect false touches is needed. 
       FIG. 4  illustrates in a top view a metal plate  401  for use in a touch sensor embodiment. In  FIG. 4 , buttons  411  indicate designated areas for receiving a human touch. The metal plate  401  can be any appropriate conductive metal that can returnably deform in response to a human touch or stylus. The metal plate has to be able to deflect a distance sufficient to cause a change in the capacitance value associated with a sensor that can be reliably detected, and the metal plate must be able to return to the original position. This action of deflection and return must be repeatable for thousands or millions of times without changing the normal position of the metal plate. Metals such as stainless steel and aluminum can be used. While the thickness needed to facilitate the deflection and return depends on the material and the overall size of the areas designated as touch areas, an example is an aluminum metal plate  301  having a thickness of 0.5 millimeters with a sensor 20 mm in diameter. Larger touch areas and larger sensor areas will provide additional sensitivity, but larger sensors also result in additional area needed, so a design tradeoff exists. 
     In  FIG. 4 , the designated areas for touch are shown as a plurality of numerical buttons. The interpretation of the meaning of a touch is very flexible and is system dependent. Characters can be used such as letters, symbols, words such as “STOP”, “START”, and international symbols for power on/off. A processor such as a microcontroller, microprocessor, digital signal processor, or central processing unit can receive a signal indicating the touch detection. The processor can be programmed to perform desired actions in response to the touch. Visual feedback such as illuminating an LED or showing a character on a panel in response to the touch can be used. This positive feedback can assure a user that the touch has been received. Haptic feedback such as vibration can be used. Other feedback indications such or light or sound in response to the touch can assist users in entering data using the touch sensor. 
       FIG. 5  illustrates in a projection view  500  a reverse side of a metal plate  501  for use in an embodiment. The opposing planar surface or reverse side  504  is the reverse of the first planar surface shown in the example metal plate  401  of  FIG. 4 , and includes other features. The areas  511  correspond to the reverse of the designated touch areas  411  in  FIG. 4 . The circular areas  511  shown in  FIG. 5  are blind holes that implement the spacer for metal touch. When the touch sensor is assembled, the depth of the blind holes provide the spacing distance between the bottom surface of the metal plate in the touch areas and the sensors on the printed circuit board, which are placed adjacent to the reverse surface  504  of the metal plate  501 . The depth of the blind holes can vary. In an example, the depth ranged from 0.1-0.2 millimeters. 
     In  FIG. 5 , posts  521  are shown extending away from the opposing planar surface  504  of metal plate  501  a distance H. The posts  521  can be formed integral to the metal plate  501 . In an alternative arrangement, the posts  521  can be mounted on metal plate  501  and secured, such as by brazing or epoxy. Metal plate  501  can be stamped, bent, or molded. Each post  521  has a hole  523  formed in an exposed surface, the hole  523  extending back towards the metal plate  501 . 
     In  FIG. 5 , the metal plate  501  includes flange portions  525 . The flange portions  525  are at the outer edges of metal plate  501  and form rigid sides. The flange portions can be formed with the metal plate  501  and can be integral to it. Metal plate  501  and flanges  525  can be formed in a metal stamping operation. In an alternative example, the flange portions can be formed separately and attached by brazing, welding or epoxy. 
     In  FIG. 5 , the circular outlining areas  511  are blind holes that implement the spacer for metal touch. The depth of the blind holes defines the spacing distance “d.” When the metal plate  501  is used in a touch sensor assembly as described hereinbelow, the depth of the blind holes  511  will set the distance between the sensors on the circuit board and the opposing planar surface  504  of metal plate  501 , and thus define the capacitance value when there is no deflection in a designated touch area. 
     The posts  521  are positioned surrounding the circular blind holes  511  in the designated touch areas. The non-touch areas between the designated touch areas are supported by the posts  521 , so that a touch in a non-touch area will not cause a deflection in metal plate  501 . The posts  521  can therefore prevent a false touch detection, since no deflection in the metal plate  501  will occur when these non-touch areas are touched. 
     The holes  523  extending into the posts  521  can also be blind holes. In an alternative arrangement, the holes can be machined to receive screws or bolts. In an example arrangement, the holes  523  can receive rivets or brads. Epoxy can be used to secure the brads to the holes. 
     In another alternative arrangement, the posts  521  can end in an extension portion (not shown in  FIG. 5 ) that extends into a receiving hole in a back panel and is secured by other means. The posts  521  provide a place for a fastener component to join the assembly together, and prevent deflection of metal plate  501  in the non-touch areas. 
       FIG. 6  shows in a projection view a metal touch sensor embodiment  600 . In  FIG. 6 , the metal plate  601  is similar to the metal plate  501  in  FIG. 5 . Similar reference labels are used for those components in  FIG. 6  that are similar to those shown in  FIG. 5 , for clarity. For example, flanges  625  in  FIG. 6  correspond to flanges  525  in  FIG. 5 . In  FIG. 6 , metal plate  601  has a first planar surface (not visible in the view in  FIG. 6 ) with designated areas for touch sensors. In  FIG. 6 , the opposing planar surface  604  is shown with posts  621  extending away from the opposing planar surface  604 . The posts  621  are shown with holes  623  extending into the posts towards the opposing planar surface  604 . The holes  623  are arranged to receive fastener components. In  FIG. 6 , the joining components  635  are shown positioned for insertion into the holes  623  in posts  621 . A circuit board  609  is shown positioned with a first surface (not visible in the projection of  FIG. 6 ) carrying sensors (also not visible in  FIG. 6 ) that are placed spaced from and opposing designated areas for touch on metal plate  601 . 
     A back cover  633  is shown overlying a second surface of circuit board  609  and is arranged to be secured to the assembly  600  by the joining components  635 . The back cover can be formed of two pieces, and can include a non-conductive spacer (not shown in  FIG. 6 ) that has openings similar to those in circuit board  609  to allow the posts  621  to extend through the spacer. In an example an acrylic spacer was used. In an alternative, the back cover  633  can be a thicker single piece as shown in  FIG. 6  and can be a conductive metal. In another alternative, the circuit board  609  can be thicker than the height of posts  621 , in which case the spacer is not needed. In the example shown in  FIG. 6 , the circuit board  609  has openings to allow the posts  621  to extend through the circuit board to receive the fasteners. The fasteners  635  will extend through the holes in back cover  633  and into the holes  623  in the posts  621 . The openings in circuit board  609  should be a bigger size than the cross-sectional area of posts  621  so that the circuit board  609  can be inserted with the posts  621  extended out of the circuit board  609 . 
     The backing cover  633  is used to press the surface of circuit board  609  close to opposing planar surface  604  of metal plate  601 . In an example, the backing cover  633  includes an acrylic spacer (not shown) and a metal cover. The thickness of the acrylic spacer plus the thickness of circuit board  609  should be bigger than the height of posts  621 . When the assembly  600  is complete, the fastener components  635  will be inserted into the holes  623  in posts  621 , will join the circuit board  609  to the metal plate  601 , and will join the backing cover  633  to complete the assembly  600 . The spacing between the sensors on the circuit board (not visible in this view) and the opposing planar surface  604  of metal plate  601  will be maintained by the depth of blind holes  511  (see  FIG. 5 ). 
     In this example, the fastener components  635  can be screws, rivets, brads, or pins inserted into the holes  623  in posts  621 . The fastener components may be mechanically coupled to metal plate  601  by rotation into threaded holes, in the case of screws, or by expansion into a blind hole, in the case of rivets. Epoxy or other adhesives can be used to secure the fastener components  635  to the posts  621 . In an alternative arrangement (not shown in  FIG. 6 ), the posts  621  can include an extended central portion that extends through the circuit board  609  and is secured to the backing component  633  using holes in  633  or by other securing methods. 
     The circuit board  609  can be of any material used for carrying circuitry and conductive traces such as “greenboard” or FR4. Single layer, dual layer and multilayer printed circuit boards can be used. Laminate substrate materials for circuitry can be used. Other layers suitable for forming circuitry including conductive sensors can be used. The backing cover  633  can be any material that is protective and provides durable mechanical support, including plastic, FR4, fiberglass, or metal. The assembly  600  can be hermetically sealed. The assembly  600  can be made water resistant or waterproof. Protective covering layers can be used with both the first planar surface of metal plate  601 , the backing cover, and the flanges. Because the change in capacitance that is sensed is due to a deflection of metal plate  601 , use of a covering material does not interfere with the touch detection. Gloves, styli, and other pointing devices can be used to deflect the metal plate  601  in the designated touch areas. 
     The embodiment in  FIG. 6  prevents false touch detection by securing the non-touch areas to the posts, so that an inadvertent touch in a non-touch area does not cause a deflection in the metal plate that can be detected by the sensors. 
       FIG. 7  shows in a projection view an alternative embodiment  700 . In  FIG. 7 , a metal plate  701  is shown with four example designated areas for touch sensors  708 . Each designated area  708  has a blind hole extending into the metal plate  701 . The metal plate  701  has a first thickness great enough to prevent deflection by a human touch. The blind holes  708  extend into the metal plate  701  and form a designated area in metal plate  701  that is thin enough that it can be repeatedly and returnably deformed by a human touch. Since the metal plate  701  is relatively thick in areas that are not designated areas for touch sensors, no deflection will occur in these areas when touched, and no false touch detection is possible. 
     To complete the capacitive sensors for the embodiment in  FIG. 7 , sensors  703  are placed on a top portion of pillars  706  extending into the blind holes  708  to set a spacing distance between the sensors and the bottom surface of the metal plate  701  (not visible in  FIG. 7 ) in the blind holes. This spacing becomes the distance “d” between the capacitor plates. 
     A circuit board  709  has pillars  706  that extend into the blind holes  708  and support the sensors  703 . Although not shown in  FIG. 7  for clarity, electrical connections are formed between the sensors  703  and the remaining circuitry on the circuit board  709 . Vertical conductive vias can be formed in the pillars  706 . Alternatively, wires or copper conductors formed on the pillars can extend vertically to complete the connections. 
     The bottom planar surface of metal plate  701 , labeled  704 , will contact the upper surface of circuit board  709  and can be adhesively or mechanically joined to complete the assembly  700 . As the metal plate  701  has a thickness so great that it cannot be deflected by human touch in non-touch areas, no false touch will be detected using this arrangement. 
       FIG. 8  shows in another projection an alternative embodiment  800 . In  FIG. 8 , a metal plate  801  similar to metal plate  701  is shown. Metal plate  801  has a thickness great enough that it is not deformable by human touch. A first planar surface (not visible in the view in  FIG. 8 ) provides designated areas for touch sensors. A plurality of blind holes  808  are formed extending into the metal plate  801  from the opposing planar surface  804 . The blind holes  808  extend into metal plate  801  leaving a thin portion having a second smaller thickness in metal plate  801  that is thin enough to be returnably deformed by human touch. The deflections in these designated areas for touch will cause a change in capacitance in these touch sensor areas. 
     In  FIG. 8 , conductive springs  812  are shown arranged in correspondence with the blind holes  808 . The conductive springs support sensors  803  positioned on a top portion of the springs  812 . The conductive springs  812  are electrically coupled to the sensors  803  and to additional circuitry on the circuit board  809 . A spacing distance is formed by inserting the springs  812  and the sensors  803  into the blind holes  808 , the sensors being placed in a position facing the opposing surface of metal plate  801  in the designated areas so that the portion of the metal plate  801  forms one plate of a capacitor, and the sensors form another plate. Placing the sensors into the blind holes in close proximity to the reverse surface (not shown) of plate  801  in the designated areas increases the capacitance and increases the sensitivity of the capacitive sensors to changes caused by deflection in plate  801 . 
     Because plate  801  cannot be deflected by a human touch in non-touch areas, no false touch detections occur due to touches in these areas. 
       FIG. 9  shows in another projection view an additional alternative embodiment  900 . In  FIG. 9 , a metal plate  901  is spaced from and overlying a circuit board  903 . A plurality of designated touch areas  911  are indicated on a first planar surface  902  of metal plate  901 . However, the designated touch areas  911  are not different from other areas on the first planar surface  902 , other than the designated touch areas are painted or labeled with visual indicators for a user. The designated touch areas  911  can appear as buttons or as other shapes. The designated touch areas can be indicated by paint, screen-printing, decals, etching, dyes and other coloration of the metal plate  901 . A plastic overlay can carry the visual indicators showing the user where the designated touch areas are on the upper planar surface  902  of the metal plate  901 . 
     In the embodiment  900 , software emulation is used to distinguish a touch in a designated touch area from a touch in other areas. The sensors  903  are arranged in an array of rows and columns, spaced from and facing the opposing planar surface (not visible in  FIG. 9 ) of the metal plate  901 . A processor and additional circuitry coupled to or located on the circuit board  903  emulates the touch areas and the non-touch areas. When a touch is detected by a change in capacitance indicating a deflection in metal plate  901  at one or more of the sensors  903 , the processor performs a method for determining which of the designated touch areas  911  the touch corresponds to. If the touch is between two designated areas, the processor makes a determination using probability and the proximity of the active sensors to the designated touch areas as to whether or not the touch is in a designated touch area. If the processor finds the touch is not in a designated touch area, the touch is disregarded as a false touch. 
     In the embodiment  900  of  FIG. 9 , the metal plate can be deflected by a human touch in designated areas  911  and in other areas. By using a software emulation approach, the posts, screws, or blind holes as used in the embodiments of  FIGS. 6-8  are not needed. The metal plate  901  can have a uniform thickness and need not have posts or other shapes or blind holes formed in it. The thickness of metal plate  901  is chosen so that the metal plate  901  can be returnably deformed in an area corresponding to a sensor area by a human touch. 
       FIG. 10  illustrates in a circuit schematic a system embodiment  1000 . In  FIG. 10 , a touch sensor  1001  includes sensors  1003  that are coupled to a mixed signal processor  1051 . Mixed signal processors (MSPs) produced specifically for use with touch sensors are provided by Texas Instruments Incorporated. As an example, the device designated MSP430FR26XX from Texas Instruments Incorporated integrates a programmable microcontroller with a dedicated analog to digital converter and with built in scan I/Os in a single device. This programmable MSP device can operate in a low power mode where the capacitive sensors are scanned while the processor and other functions “sleep”. When a touch is detected, the device “wakes up” and begins processing the touches detected. Ultra-low power processors are particularly important for applications powered by batteries. Texas Instruments Incorporated provides other integrated circuits arranged specifically for touch sensor applications that can be used with the embodiments. In alternative examples, other microprocessors, micro-controllers, digital signal processors, and analog to digital converters can be used to form the circuitry of  FIG. 10 . Application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and complex programmable logic devices (CPLDs) can also be used to form the processor  1051 . Processor  1051  includes non-volatile program memory stored in FLASH, EEPROM, or FRAM that can be used to store instructions for the microcontroller or processor to execute. Processor  1051  includes communications ports labeled UART/SPI/IIC and GPIO for coupling the dedicated processor  1051  to the remaining circuitry of the system. 
     In operation, the processor  1051  can provide the software emulation needed to eliminate false touch detection using an array of sensors such as  1003  on a circuit board mounted to a metal plate. When a touch is detected, the processor can determine which sensor or sensors are touched. The processor can then determine whether the sensor or sensors are located in a position that corresponds to a designated touch area. If the touch is in an area that is not a designated touch area, then this touch is a false touch and can be ignored. 
       FIG. 11  illustrates in a flow diagram a method embodiment  1100 . In  FIG. 11 , the method begins at step  1101 , Idle. In an example, a processor can optionally be put in a low power or sleep mode in this step. In an alternative example, the processor can remain active in this step. At step  1103 , which can be performed periodically from step  1101 , the sensors are scanned. In scanning the sensors, a change in capacitance is detected for any sensors where the metal plate overlying the sensors is deflected by a touch. 
     At step  1105 , a touch detected? determination is made. If the sensor scan did not result in any sensors indicating a touch, the method returns to step  1101 , Idle, and continues. 
     If a touch was detected and the determination in step  1105  is true, then the method transitions to step  1107 . This optional step indicates the processor should wake (if in a sleep mode). At step  1109 , a second determination is made. Using the sensors that were active in step  1105 , a decision is made as to whether the touch corresponds to a designated area for touch in the touch sensor. If the decision is false, then the touch is in an area not designated for touch, and it can be ignored. In that case the method transitions back to step  1101 , Idle. 
     If the determination at step  1109  is true, the method transitions to step  1113 , where the touch is processed as a valid user input. Actions can be taken or the touch information can be stored awaiting additional touch input. For example, in a security application, several touch inputs may be needed to enter a code or password before the system can evaluate whether the code or password matches a stored code or password. 
     By providing a method to distinguish false touches from touch inputs at a designated area, and by ignoring false touches at a metal sensor, the method of  FIG. 11  emulates in software the function of the posts in the embodiment shown in  FIGS. 5 and 6 ; without the need for adding posts to the metal plate. 
       FIG. 12  shows in another projection view an additional embodiment. In  FIG. 12 , a metal plate  1201  provides an upper planar surface  1202  for receiving touch inputs. A circuit board  1209  includes a plurality of sensors  1203  arranged in rows and columns and can include additional circuitry such as processors and analog to digital converter circuitry to collect and process signals from the sensors. 
     The metal plate  1201  can be a touch sensor that can receive input in the form of gestures such as a swipe or loop or diagonal or parallel line drawn by human touch. When the sensors sense a change in capacitance due to the deflection of the metal plate, the deflection can be detected as a gesture. By analyzing the changes in capacitance in multiple sensors, and by determining the order of the sensors that were affected, a touch movement can be interpreted as an input. 
       FIG. 13  depicts in a projection a metal plate  1301  that is similar to the metal plate of  FIG. 12 . In  FIG. 13 , the opposite planar surface is shown. A recessed portion  1310  is formed corresponding to the sensor area, and a flange  1325  is formed surrounding the recessed portion  1310 . The flange portion  1325  of the metal plate  1301  has a thickness greater than the portion of the metal plate in the recessed portion  1310 . The flange thickness sets a spacer depth between the array of sensors (not shown in  FIG. 13 ) on a circuit board and the opposing planar surface of the metal plate  1301 . 
       FIG. 14  depicts in a projection view  1400  an alternative embodiment metal plate. In  FIG. 14 , a metal plate  1401  is shown that is configured for a sliding input. In  FIG. 14 , the opposing planar surface of the metal plate  1401  is shown, the upper planar surface of metal plate  1401  is not visible in this view. In  FIG. 14 , a flange  1425  surrounds a recessed portion  1410  that corresponds to the array of sensors on a circuit board (not shown in  FIG. 14 ). The thickness of the flange portion  1425  again sets a spacer depth for the capacitive sensors. A user can input a touch input to the sensor shown in  FIG. 14  by sliding a finger in a single motion. Sliding inputs to touch sensors are particularly useful for inputting variable settings such as volume and brightness. 
     In addition to the embodiments described, a wheel touch pad can be formed using the array of sensors such as sensors  1203  in  FIG. 12 . By making a motion in a circular direction in a designated area, a user can input a command. Fast forward and rewind commands for audio players and video players can be input using wheel sensors, for example. A visual pattern illustrating the wheel pattern can be printed on the upper planar surface of the metal plate to guide the user. 
     In the embodiments and examples described above, the sensors can be capacitive sensors with a pad or plate on the printed circuit board. In alternative arrangements that form additional embodiments, the sensors on the circuit board can be inductive sensors. A coil can be formed in the sensor area at each sensor position. An electric field can be formed around the coil. When the metal plate is deflected by a human touch, the change in the electric field can be detected and the deflection due to the touch can be detected. 
     In an example embodiment, an apparatus includes a metal plate having a plurality of defined areas forming touch sensors on an first planar surface, and having an opposing planar surface, the metal plate configured to be deformable in the plurality of defined areas by a human touch, and the metal having non-touch areas in areas other than the defined areas. The apparatus includes a circuit board having a plurality of conductive sensors on a first surface arranged with the plurality of conductive sensors, facing and spaced from the opposing planar surface of the metal plate, the conductive sensors placed in correspondence with the defined areas on the metal plate so that deflection sensors are formed in the defined areas by the conductive sensors and the opposing planar surface of the metal plate. 
     In a further example, in the apparatus, the metal plate has a first thickness and includes a plurality of blind holes extending into the metal plate at the opposing planar surface to provide a second thickness of the metal plate less than the first thickness in the plurality of defined areas. In still another example, the apparatus includes a plurality of pillars on the circuit board extending into the plurality of blind holes and having at least one of the plurality of conductive sensors at a top surface of the pillars facing and spaced from the opposing planar surface of the metal plate, a deflection sensor being formed between the at least one of the defined areas of the metal plate and at least one of the plurality of conductive sensors at the top surface of the pillar. 
     In yet another example, the apparatus includes a plurality of spring pillars on the circuit board extending into the plurality of blind holes in the metal plate and having at least one of the plurality of conductive sensors at a top portion of the spring pillars facing and spaced from the opposing planar surface of the metal plate, at least one deflection sensor being formed between the opposing planar surface of the metal plate in the defined areas and the at least one of the plurality of conductive sensors at the top portion of the spring pillars. 
     In still a further example, the apparatus includes a plurality of posts formed on the opposing planar surface of the metal plate and extending away from the opposing planar surface a predetermined distance, and blind openings extending into a top surface of the plurality of posts for receiving a fastener. 
     In yet another example, the apparatus includes the plurality of posts placed around the defined areas to prevent the metal plate from deforming in the non-touch areas. 
     In still another example, the apparatus includes fasteners inserted in the blind openings in the plurality of posts to join a backing component covering a second planar surface of the circuit board to the metal plate. In yet another example, the apparatus includes the fasteners selected from screws, rivets, brads and pins. 
     In another example, in the apparatus, wherein the metal plate is selected from stainless steel and aluminum. In yet another example, the conductive sensors are selected from capacitive sensors and inductive sensors. 
     In another alternative embodiment, an apparatus includes: a metal plate having at least one defined area forming a touch sensor on a first planar surface, and having an opposing planar surface, the metal plate being deformable in the defined area by a human touch on the first planar surface; and a recessed portion on the opposing planar surface of the metal plate having a recess depth. In the apparatus, the recess depth defines a spacing distance; and the apparatus includes flange portions surrounding the recessed portion on the opposing planar surface of the metal plate and not having the recess depth; a circuit board having a plurality of sensors on an upper surface, the sensors arranged in rows and columns, the plurality of sensors placed facing and in correspondence with the recessed portion of the opposing planar surface of the metal plate. In the apparatus, the flange portions contact the upper surface of the circuit board, and the sensors are spaced from the opposing planar surface of the metal plate by the spacing distance. 
     In still another example, in the apparatus, the touch sensor of the metal plate forms a gesture sensor area. In a further example, in the apparatus, the touch sensor of the metal plate forms a sliding sensor area. In yet another example, in the apparatus, the touch sensor of the metal plate forms a wheel sensor area. 
     In still an alternative example, in the apparatus the plurality of sensors comprise capacitive sensors that change capacitance when an area of the metal plate is deflected by a human touch. In yet another example, in the apparatus the plurality of sensors comprise inductive sensors that form an electric field that changes when an area of the metal plate is deflected by a human touch. In a further example, in the apparatus the defined area further include a plurality of defined button areas forming touch sensor buttons, spaced apart by areas on the metal plate forming non-touch areas. In yet another example, in the apparatus a processor is coupled to the sensors, and configured to detect a change in capacitance in the sensors indicating a touch deflecting the metal plate, and is configured to determine whether the touch is within a defined button area. 
     In a method embodiment, the method includes: defining a touch area on a first planar surface of a metal plate, the metal plate having a second planar surface opposing the first planar surface, the metal plate having a thickness in the touch area such that the metal plate can be deflected in the touch area by a human touch; placing a plurality of sensors on a circuit board disposed facing and spaced from the second planar surface of the metal plate; coupling the plurality of sensors to a processor configured to detect a signal from the sensors corresponding to deflection of the metal plate in the touch area due to a human touch; scanning the plurality of sensors to detect a deflection in the metal plate caused by a human touch; and operating the processor to determine where in the touch area the touch occurred. 
     In yet another alternative example, the method further includes defining touch button areas within the touch area on the first planar surface of the metal plate, and further defining non-touch areas; and operating the processor to determine whether a deflection in the metal plate detected by the plurality of sensors corresponds to a touch in a defined touch button area. 
     Modifications are possible in the described embodiments, and other embodiments are possible within the scope of the claims.