Abstract:
Backing lighting of induction touch keys is accomplished with a spacer layer surrounding an inductive touch sensor coil and a light source on a substrate, and light transmissive layer having a suspended metal disk proximate to the inductive touch sensor coil. A protective fascia may be placed over the light transmissive layer and spacer layer. When the light transmissive layer is displaced toward the inductive touch sensor coil the impedance value of the inductive touch sensor coil changes and the change is detected. Materials used that are translucent (light transmissive) may be continuous and solid, and opaque materials may have openings therein for transmission of light therethrough.

Description:
RELATED PATENT APPLICATION 
       [0001]    This application claims priority to commonly owned U.S. Provisional Patent Application Ser. No. 61/238,718; filed Sep. 1, 2009; entitled “Backlighting Inductive Touch Buttons,” by Stephen B. Porter and Keith E. Curtis; and is hereby incorporated by reference herein for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to inductive touch sensor keys or buttons, and, more particularly, to backlighting of the inductive touch sensor keys or buttons. 
       BACKGROUND 
       [0003]    Each inductive touch sensor key or button comprises an inductive sensor on a substrate, a thin non-magnetic spacer layer over the inductive touch sensor, and a deformable metal target layer (e.g., key or button) over the thin non-magnetic spacer layer. When the deformable metal target layer is depressed, the inductive sensor detects a change in its impedance. This change in impedance is detected and is used to indicate that the key or button has been pressed. A problem exists however in that the deformable metal target layer is light opaque and therefore precludes backlighting thereof. Existing published solutions for inductive touch sensor designs are mechanically very thin. They rely on simple flat spacer layers less than 0.020 inch thick and continuous conductive metal sheets for targets that do not allow light to pass therethrough. 
       SUMMARY 
       [0004]    Therefore what is needed is a way to backlight inductive touch sensor keys or buttons. According to the teachings of this disclosure, a molded spacer layer and a discrete metal disk may be used for the inductive target. By using either reverser mount or side illuminating LED(s) with a suspended metal target, inductive touch sensor keys may be backlit. Backlighting of inductive touch sensor keys or buttons is especially desirable for use in appliances, automotive controls, consumer products such as television set top box converters for cable or satellite television reception, security entry pads, intercom buttons, computers, industrial control panels, etc. Backlighting of the keys or buttons may be used to indicate that the key or button has been pressed, e.g., visual feedback, and/or improved visibility under poor lighting conditions. 
         [0005]    There are several things that are needed to complete backlighting for inductive touch buttons. Inductive touch buttons in most cases require that the metal fascia be the target, but according to the teachings of this disclosure it would be moved away from the inductive coil to the point where it will not work as the target. To counteract this, a suspended target proximate to the inductive sensor coil is used. By configuring the lighted inductive touch buttons as such, height may be added to the inductive touch panel design that will allow placement of light emitting diodes (LEDs) on the top and/or bottom side(s) of the circuit board comprising the inductive sensor coil. 
         [0006]    By moving the front button layer farther from the substrate, e.g., inductive touch printed circuit board (PCB), a molded plastic layer(s) may be used to create light pipes that allow for backlighting of the inductive touch sensor buttons. A metallic target layer is attached and/or molded on the plastic layer proximate to the inductive sensor coil. As this metallic target layer moves closer to the inductor sensor coil when the button is depressed, the impedance of the inductor sensor coil thereby changes and is detected. The metallic target layer may also be used as a shield to prevent or reduce hot (bright) spots in the lighting of the inductive touch sensor button. 
         [0007]    The material that holds the suspended metallic target may be translucent and function as a light pipe for the light from a light source, e.g., light emitting diodes (LEDs). This translucent material may also function as a seal for the holes that may now be placed in the metal cover to allow light to pass therethrough. The material that is used as the spacer surrounding the inductive coil may be of a non-translucent material so as to prevent bleeding of light from one adjacent button to the next. 
         [0008]    The light source LEDs do not have to be mounted on the top side of the circuit board, as they can be mounted elsewhere as needed. Also the top layer does not have to be flat or even metal, and it may be curved or use an over-mold process for sealing of the button. 
         [0009]    According to a specific example embodiment of this disclosure, a backlit inductive touch sensor key comprises: a substrate; an inductive sense coil on the substrate; a light source; a spacer layer on the substrate and having an opening that surrounds the inductive sense coil and the light source; and a over-layer having opening therein to allow light to pass therethrough from the light source, the over-layer is attached to the spacer layer and forms a light transmission cavity between the substrate and the over-layer; and an over-mold button attached to a side of the over-layer opposite to the light transmission cavity, the over-mold button being light transmissive; wherein when the over-mold button is biased toward the inductive sense coil, an impedance value of the inductive sense coil changes. 
         [0010]    According to another specific example embodiment of this disclosure, a backlit inductive touch sensor key comprises: a substrate; an inductive sense coil on the substrate; a light source; a spacer layer on the substrate and having an opening that surrounds the inductive sense coil and the light source; and a flexible layer of light transmissive material, the flexible layer is over the inductive sense coil and light source, and is attached to the spacer layer wherein a light transmission cavity is formed between the substrate and the flexible layer; wherein when the flexible layer is biased toward the inductive sense coil, an impedance value of the inductive sense coil changes. 
         [0011]    According to yet another specific example embodiment of this disclosure, a backlit inductive touch sensor key comprises: a substrate; an inductive sense coil on the substrate; a light source; a spacer layer on the substrate and having an opening that surrounds the inductive sense coil and the light source; a flexible fascia layer adapted to allow light therethrough, the flexible fascia layer is over the inductive sense coil and light source, and is attached to the spacer layer wherein a light transmission cavity is formed between the substrate and the flexible fascia layer; a light translucent layer attached to a side of a portion of the flexible fascia layer facing and inside of the light transmission cavity; and a metal target attached to a face of the light translucent layer proximate to the inductive sense coil; wherein when the flexible fascia layer is biased toward the inductive sense coil, an impedance value of the inductive sense coil changes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A more complete understanding of the present disclosure thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings wherein: 
           [0013]      FIG. 1  is a schematic block diagram of an electronic system having an inductive touch keypad, an inductive touch analog front end and a digital processor, according to the teachings of this disclosure; 
           [0014]      FIG. 2  is a schematic elevational view of a back-lighted inductive touch key comprising a light transmissive button in combination with an over-layer having holes therein for light to pass therethrough, according to a specific example embodiment of this disclosure; 
           [0015]      FIG. 3  is a schematic elevational view of a back-lighted inductive touch key comprising a light transmissive layer and a protective over-layer adapted for light to pass therethrough, according to another specific example embodiment of this disclosure; and 
           [0016]      FIG. 4  is a schematic elevational view of a back-lighted inductive touch key comprising a flat fascia adapted for light to pass therethrough, according to yet another specific example embodiment of this disclosure. 
       
    
    
       [0017]    While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0018]    Referring now to the drawings, the details of an example embodiment is schematically illustrated. Like elements in the drawings will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix. 
         [0019]    Referring to  FIG. 1 , depicted is a schematic block diagram of an electronic system having an inductive touch keypad, an inductive touch analog front end and a digital processor, according to the teachings of this disclosure. A digital processor  106 , e.g., a microprocessor, microcomputer, digital signal processor (DSP), application specific integrated circuit (ASIC), programmable logic array (PLA), etc., is coupled to an inductive touch analog front end (AFE)  104  and a matrix of inductive touch sensor keys  102 , e.g., pushbuttons, levers, toggles, targets, handles, knobs, etc. Typical inductive touch sensor keys  102  may comprise Microchip inductive mTouch™ sensors more fully described at www.microchip.com. The digital processor  106  and AFE  104  may be part of a mixed signal (analog and digital circuits) integrated circuit device. 
         [0020]    The inductive touch AFE  104  facilitates, with a single low-cost integrated circuit device, all active functions used in determining when there is actuation of inductive sensors, e.g., by pressing and deflecting a target key that changes the impedance value of an associated inductive sensor. The inductive touch AFE  104  measures the impedance value of each sensor of the matrix of inductive touch sensor keys  102  and converts the impedance values into respective analog direct current (dc) voltages that are read and converted into digital values by the digital processor  106 . 
         [0021]    The digital processor  106  supplies clock and control functions to the inductive touch AFE  104 , reads the analog voltage detector output of the inductive touch AFE  104 , and selects each key of the matrix of inductive touch sensor keys  102 . When actuation of a key of the matrix of inductive touch sensor keys  102  is determined, the digital processor  106  will take an appropriate action. 
         [0022]    According to the teachings of this disclosure, each key (touch buttons) of the matrix of inductive touch sensor keys  102  is illuminated, as more fully disclosed hereinafter. 
         [0023]    Referring to  FIG. 2 , depicted is a schematic elevational view of a back-lighted inductive touch key comprising a light transmissive button in combination with an over-layer having holes therein for light to pass therethrough, according to a specific example embodiment of this disclosure. A back-lighted inductive touch key  102   a  comprises a substrate  210 , e.g., printed circuit board (PCB); an inductive sense coil  220 , a light source, e.g., light emitting diodes (LEDs)  218 ; a non-translucent (opaque) molded spacer layer  212  surrounds the inductive sense coil  220  and LEDs  218 , an over-layer  214  having openings therein for light from the LEDs  218  to pass therethrough, and an over-mold button  216  that is translucent for illumination thereof by the light from the LEDs  218 . In addition, if the over-layer  214  is non-metallic then a metallic target  222  is disposed on a surface of the over-layer  214  proximate to the inductive sense coil  220 . A metallic over-layer  214  may be for example, but is not limited to, aluminum, steel, stainless steel, copper, titanium, etc. A non-metallic over-layer  214  may be for example, but is not limited to, plastic, Teflon, polyamide, etc. 
         [0024]    The molded spacer layer  212  surrounding the inductive sense coil  220  and LEDs  218  is substantially non-translucent (opaque) so that light does not bleed over to another adjacent back-lighted inductive touch key (not shown). The LEDs  218  (light source) may be mounted on top of the substrate  210 , and inside of a cavity  226  formed by the substrate  210 , the molded spacer layer  212  and the over-layer  214 . The LEDs  218  may also be mounted in the substrate  210  or on the opposite side thereof (e.g., LED  318   a  or LED  318 , respectively, of  FIG. 3 ). LEDs  218  may be on either side and/or inside of the inductive sense coil  220 . 
         [0025]    The over-mold button  216  is flexible wherein when pushed (actuated) by an external force, e.g., push from a finger, the over-layer  214  portion over inductive sense coil  220  moves closer thereto and thereby changes the impedance thereof. If the over-layer  214  is non-metallic and does not affect the impedance of the inductive sense coil  220 , then a metallic target  222  may be attached to the over-layer  214  proximate to the inductive sense coil  220 . The inductive touch AFE  104  ( FIG. 1 ) detects this change in impedance of the sense coil  220  and indicates this event to the digital processor  106  for appropriate action to be taken. For example, but not limited to, a change in intensity and/or color of the light from the LEDs  218  may indicate successful actuation of this specific inductive touch sensor key  102   a . It is contemplated and within the scope of this disclosure that the over-layer  214  portion over the inductive sense coil  220  and/or the target  222  may be any type of material that affects the impedance value of the inductive sense coil  220  when there is a change in distance therebetween. 
         [0026]    Referring to  FIG. 3 , depicted is a schematic elevational view of a back-lighted inductive touch key comprising a light transmissive layer and a protective over-layer adapted for light to pass therethrough, according to another specific example embodiment of this disclosure. A back-lighted inductive touch key  102   b  comprises a substrate  310 , e.g., a printed circuit board (PCB); an inductive sense coil  320 , a light source, e.g., light emitting diodes (LEDs)  318  and/or  318   a ; a non-translucent (opaque) molded spacer layer  312  surrounds the inductive sense coil  320  and LEDs  318 , a light transmissive layer  316 , a metallic target  322  attached to the layer  316  and proximate to the inductive sense coil  320 , and an over-layer  314  that a portion thereof is either light transmissive or has openings therein for light from the LEDs  318  to pass therethrough. 
         [0027]    The molded spacer layer  312  surrounding the inductive sense coil  320  and LEDs  318  and/or  318   a  is substantially non-translucent (opaque) so that light does not bleed over to another adjacent back-lighted inductive touch key (not shown). The LEDs  318  (light source) may be mounted on top of the substrate  310  (e.g., LED  218  of  FIG. 2 ) and inside of a cavity  326  formed by the substrate  310 , the molded spacer layer  312  and the light transmissive layer  316 . The LEDs  318   a  may also be mounted in the substrate  310  or on the opposite side thereof, e.g., LED  318 . LEDs  318  may be on either side and/or inside of the inductive sense coil  320 . 
         [0028]    The light transmissive layer  316  may be flexible wherein when pushed (actuated) by an external force, e.g., push from a finger, the light transmissive layer  316  portion over inductive sense coil  320  moves closer thereto and thereby changes the impedance thereof. If the light transmissive layer  316  is not made of a flexible and/or light transmissive material then openings or gaps  324  may be disposed within a portion of the light transmissive layer  316  for light from the LEDs  318  to pass therethrough. 
         [0029]    The over-layer  314  may be used for protection from physical abuse and/or harmful water and/or chemical infiltration. The over-layer  314  may comprise a thin metal layer, e.g., aluminum, steel, stainless steel, copper, titanium, etc. or a non-metallic layer, e.g., plastic, Teflon, polyamide, etc. If the material of the over-layer  314  is not light transmissive then opening may be placed therein (not shown) for light transmission therethrough. 
         [0030]    If the light transmissive layer  316  is non-metallic and does not affect the impedance of the inductive sense coil  320 , then a metallic target  322  may be attached to the light transmissive layer  316  proximate to the inductive sense coil  320 . The inductive touch AFE  104  ( FIG. 1 ) detects a change in impedance of the sense coil  320  and indicates this event to the digital processor  106  for appropriate action to be taken. For example, but not limited to, a change in intensity and/or color of the light from the LEDs  318  may indicate successful actuation of this specific inductive touch sensor key  102   b . It is contemplated and within the scope of this disclosure that the light transmissive layer  316  and/or the target  322  over the inductive sense coil  320  may be any type of material that affects the impedance value of the inductive sense coil  320  when there is a change in distance therebetween. The target  322  may also provide light shielding an light diffusion from the light source, e.g., LED  318   a , so as to prevent light intensity “hot spots” in the back-lighted inductive touch key  102   b.    
         [0031]    Referring to  FIG. 4 , depicted is a schematic elevational view of a back-lighted inductive touch key comprising a flat fascia adapted for light to pass therethrough, according to yet another specific example embodiment of this disclosure. A back-lighted inductive touch key  102   c  comprises a substrate  410 , e.g., a printed circuit board (PCB); an inductive sense coil  420 , a light source, e.g., light emitting diodes (LEDs)  418 ; a non-translucent (opaque) molded spacer layer  412  surrounds the inductive sense coil  420  and LEDs  418 , a light transmissive (translucent) layer  416 , a metallic target  422  attached to the layer  416  and proximate to the inductive sense coil  420 , and an over-layer fascia  414  that a portion thereof is either light transmissive or has openings therein for light from the light transmissive layer  416  to pass therethrough. 
         [0032]    The over-layer fascia  414  may be substantially flat and attached to the non-translucent (opaque) molded spacer layer  412  for support thereof. The light transmissive layer  416  is attached to the over-layer fascia  414  and in cooperation therewith moves the metallic target  422  closer to the inductive sense coil  420  when a force is applied to the over-layer fascia  414  proximate to the light transmissive layer  416 . The light transmissive layer  416  serves as a light pipe for illumination of an information area of the over-layer fascia  414 . The material of the over-layer fascia  414  may comprise metal or be nonmetallic as desired, and if this material is opaque (non-light transmissive), openings  428  therein may be provided for light to pass therethrough. 
         [0033]    The molded spacer layer  412  surrounding the inductive sense coil  420  and LEDs  418  is substantially non-translucent (opaque) so that light does not bleed over to another adjacent back-lighted inductive touch key (not shown). The LEDs  418  (light source) may be mounted on top of the substrate  410  (e.g., LED  218  of  FIG. 2 ) and inside of a cavity  426  formed by the substrate  410 , the molded spacer layer  412  and the over-layer fascia  414 . The LEDs  418  may also be mounted in the substrate  410 , e.g., LED  318   a . LEDs  418  may be on either side and/or inside of the inductive sense coil  420 . The over-layer fascia  414  may be used for protection from physical abuse and/or harmful water and/or chemical infiltration. The over-layer fascia  414  may comprise a thin metal layer such as for example, but is not limited to, aluminum, steel, stainless steel, copper, titanium, etc., or a non-metallic layer such as for example, but is not limited to, plastic, Teflon, polyamide, etc. 
         [0034]    The inductive touch AFE  104  ( FIG. 1 ) detects a change in impedance of the sense coil  420  and indicates this event to the digital processor  106  for appropriate action to be taken. For example, but not limited to, a change in intensity and/or color of the light from the LEDs  418  may indicate successful actuation of this specific inductive touch sensor key  102   c . It is contemplated and within the scope of this disclosure that the light transmissive layer  416  and/or the target  422  over the inductive sense coil  420  may be any type of material that affects the impedance value of the inductive sense coil  420  when there is a change in distance therebetween. 
         [0035]    While embodiments of this disclosure have been depicted, described, and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and are not exhaustive of the scope of the disclosure.