Abstract:
A system is provided comprising a switching device and a response module. The switching device has a critical switch and a plurality of non-critical switches. The switching device generates an analog output voltage based on a switching state of the critical switch and each of the non-critical switches. The response module monitors the analog output voltage. The response module detects when the critical switch is closed, regardless of whether any non-critical switch is closed or any non-critical switch is open.

Description:
FIELD 
       [0001]    The present disclosure relates to switching devices and more particularly to a switching device with critical switch closure detection. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Electronic devices, including consumer electronic devices, appliances, and the like, often include a switching device such as a push-button keyboard input device. The keyboard may include electrical switches connected to a series of resistors and an input voltage. Depression of a keyboard push-button or “key” may close one of the switches, thereby generating an analog output voltage. The analog output voltage may be a fraction of the input voltage, depending on the configuration of the switches and resistors. An analog-to-digital converter may convert the analog output voltage to a digital output that corresponds to the depressed key. 
         [0004]    Traditionally, switching devices are biased either at the input voltage or at the circuit&#39;s ground. Thus, when no keys are pressed, the output of the switching device is either the input voltage or zero volts. When a push-button is pressed, a switch is closed causing an output between zero volts and the input voltage. Control and response circuitry may receive the output and recognize the output voltage as corresponding to the pressed key. The control and response circuitry may include and analog-to-digital converter and/or a control module for controlling a controlled device in response to the voltage output. 
         [0005]    Push-buttons, or keyboard keys, may become stuck. In the traditional system, the switching device becomes inoperable when a key is stuck as the output of the switching device also becomes stuck. Pressing another key of the keyboard may cause the switching device to output an analog output voltage that does not correspond to either the pressed key or the stuck key. 
         [0006]    Such a switching device may be implemented on an integrated circuit board (IC). The IC hosting the switching device may also host a user display, such as an LED display or an LCD panel. Control and/or response circuitry for the electronic device may be hosted on a separate IC electrically connected to the IC that is hosting the user input switching device and user display. 
         [0007]    During use of the electronic device, the two IC&#39;s may become disconnected. In the traditional system, the control circuitry is not able to detect the malfunction. When the two IC&#39;s are disconnected, the analog output voltage may simply be zero volts or the input voltage, and the control circuitry may simply read the analog output voltage as having received no user input. Thus, the control and/or response circuitry may simply proceed as if no user input has been received and no key has been depressed. In such case, the user is not able to input key presses to the control circuitry to pause operation of the controlled device or to shut down or power-off the controlled device. 
       SUMMARY 
       [0008]    A system comprising a switching device and a response module is provided. The switching device has a critical switch and a plurality of non-critical switches and generates an analog output voltage based on a switching state of the critical switch and each of the plurality of non-critical switches. The response module monitors the analog output voltage and detects when the critical switch is closed regardless of whether any non-critical switch is closed or any non-critical switch is open. 
         [0009]    A method for a switching device having a having a critical switch and a plurality of non-critical switches is also provided. The method includes generating an analog output voltage based on a switching state of the critical switch and each of the non-critical switches. The method also includes monitoring the analog output voltage and detecting when the critical switch is closed regardless of whether any non-critical switch is closed or any non-critical switch is open. 
         [0010]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
     
       DRAWINGS 
         [0011]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0012]      FIG. 1  is a schematic illustration of a switching device; 
           [0013]      FIG. 2  is a table illustrating component characteristics of a switching device; 
           [0014]      FIG. 3  is a schematic illustration of a switching device with equivalent series and parallel circuit labels; 
           [0015]      FIG. 4  is a table illustrating Vout when switches of a switching device are closed; 
           [0016]      FIG. 5  is an A/D conversion table for a switching device; 
           [0017]      FIG. 6  is a graphical illustration of an A/D conversion table for a switching device; 
           [0018]      FIG. 7  is a table illustrating Vout when a switch is stuck and when a critical switch is closed; 
           [0019]      FIG. 8  is another table illustrating Vout when a switch is stuck and when a critical switch is closed; 
           [0020]      FIG. 9  is an A/D conversion table for a stuck switch mode; 
           [0021]      FIG. 10  is a flow chart illustrating a control algorithm for a switching device; and 
           [0022]      FIG. 11  is a schematic illustration of a switching device, A/D converter, and control module. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the terms module, control module, and controller refer to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. Further, as used herein, computer-readable medium refers to any medium capable of storing data for a computer. Computer-readable medium may include, but is not limited to, CD-ROM, floppy disk, magnetic tape, other magnetic or optical medium capable of storing data, memory, RAM, ROM, PROM, EPROM, EEPROM, flash memory, punch cards, dip switches, or any other medium capable of storing data for a computer. 
         [0024]    With reference to  FIG. 1 , a switching device  100  may include switches SW 1  through SW 12  and resistors R 1  through R 15  connected to an input, or supply voltage (Vcc) and a ground  102 , or return voltage. The Vcc and the ground  102  may be generally referred to as the supply rails. While the Vcc may be a positive voltage, and while the ground may essentially be at zero volts, other voltage differentials may be used across the supply rails. 
         [0025]    The switches, SW 1  through SW 12 , may be normally open switches. The switching device  100  may be connected to a response module  112  including an analog-to-digital (A/D) converter  104  and a control module  110 . An analog output voltage (Vout) of the switching device may be received by the A/D converter  104 . The A/D converter  104  may convert Vout to a digital output which may be received by the control module. 
         [0026]    The switches, SW 1  through SW 12 , may be connected to input keys of an electronic device. For example, the switching device may be used in connection with an appliance, such as a dishwasher, oven, stove, washing machine, dryer, or the like. User input may be received via depression of keys associated with each of the switches, SW 1  through SW  12 . For example, with reference to  FIG. 11 , user keys may include numerical keys, zero through nine, and function keys, such as “pause” and “power.” The keys may be located proximate to a user display  120 , such as an LED or LCD display. 
         [0027]    With reference to  FIG. 2 , electrical characteristics of the components of the switching device depicted in  FIG. 1  are shown. As shown, resistors R 1  and R 13  may be 120 ohm resistors. Resistors R 2  through R 12  may be 1,000 ohm resistors. Resistors R 14  and R 15  may be 10,000 ohm resistors. As described in more detail below, R 14  and R 15  are “critical” resistors. The input voltage, Vcc, may be 5.45 volts. As can be appreciated, other components with different electrical characteristics may be used to accomplish the functionality described by the present teachings. Specifically, Vcc may be greater or less than 5.45 volts. Additionally, other resistors of varying resistance, greater or less than that described by  FIG. 2 , may be used. Further, while the switching device of  FIG. 1  is shown with twelve switches, SW 1  through SW 12 , more or less switches may be used. 
         [0028]    Generally, the resistance of the critical resistors, R 14  and R 15 , is much larger than the resistance of resistors R 1  through R 13 . As described in more detail below, R 14  and R 15  cause Vout to be biased between zero volts and Vcc. The large R 14  and R 15  resistors render the end switches, SW 1  and SW 12 , “critical” switches. When one of the “non-critical” switches, SW 2  through SW 11 , is stuck closed, the A/D converter and control module may still be able to recognize when SW 1  or SW 12  is closed by a user key press. 
         [0029]    When none of the switches SW 1  through SW 12  are closed, the switching device functions as a voltage divider, and Vout may be calculated according to the following formula: 
         [0000]    
       
         
           
             
               
                 
                   Vout 
                   = 
                   
                     
                       
                         R 
                          
                         
                             
                         
                          
                         14 
                       
                       
                         
                           R 
                            
                           
                               
                           
                            
                           14 
                         
                         + 
                         
                           R 
                            
                           
                               
                           
                            
                           15 
                         
                       
                     
                     × 
                     
                       Vcc 
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0030]    Thus, with R 14  and R 15  each at 10,000 ohms, and with Vcc at 5.45 volts, when none of the switches SW 1  through SW 12  are closed, Vout is 2.725 volts. 
         [0031]    When one of the switches SW 1  through SW 12  is closed, Vout may be calculated with reference to the equivalent series and parallel resistances. With reference to  FIG. 3 , when SW 4  is closed, the series resistors R 1  through R 13  may be grouped into first and second series resistance groups, RS 1  and RS 2 . RS 1  is the series equivalent resistance of the resistors “above” the closed switch. RS 2  is the series equivalent of the resistors “below” the closed switch. RS 1  and RS 2  may be calculated based on the following formulas: 
         [0000]        RS 1= R 1 + . . . + RN;    (2) 
         [0000]        RS 2= R ( N+ 1)+ . . . + R 13   (3) 
         [0000]    where N corresponds to the number of the closed switch. When SW 4  is closed, RS 1 =R 1 +R 2 +R 3 +R 4 =3,120 ohms. When SW 4  is closed, RS 2 =R 5 +R 6 +R 7 +R 8 +R 9 +R 10 +R 11 +R 12 +R 13 =8,120 ohms. 
         [0032]    With continued reference to  FIG. 3 , RP 1  is the parallel equivalent resistance of R 15  and RS 1 . RP 2  is the parallel equivalent resistance of R 14  and RS 2 . RP 1  and RP 2  may be calculated based on the following formulas: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       RP 
                        
                       
                           
                       
                        
                       1 
                     
                     = 
                     
                       
                         RS 
                          
                         
                             
                         
                          
                         1 
                         × 
                         R 
                          
                         
                             
                         
                          
                         15 
                       
                       
                         
                           RS 
                            
                           
                               
                           
                            
                           1 
                         
                         + 
                         
                           R 
                            
                           
                               
                           
                            
                           15 
                         
                       
                     
                   
                   ; 
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     RP 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       
                         RS 
                          
                         
                             
                         
                          
                         2 
                         × 
                         R 
                          
                         
                             
                         
                          
                         14 
                       
                       
                         
                           RS 
                            
                           
                               
                           
                            
                           2 
                         
                         + 
                         
                           R 
                            
                           
                               
                           
                            
                           14 
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Based on the foregoing equations (1) through (5), when a switch is closed, Vout may be calculated based on the following formula: 
         [0000]    
       
         
           
             
               
                 
                   Vout 
                   = 
                   
                     
                       
                         RP 
                          
                         
                             
                         
                          
                         2 
                       
                       
                         
                           RP 
                            
                           
                               
                           
                            
                           1 
                         
                         + 
                         
                           RP 
                            
                           
                               
                           
                            
                           2 
                         
                       
                     
                     × 
                     Vcc 
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0033]    With reference to  FIG. 4 , RS 1 , RS 2 , RP 1 , RP 2 , and Vout are shown when each of switches SW 1  through SW 12  is independently closed, given the component characteristics illustrated in  FIG. 2 . For example, when SW 4  is closed RS 1  is 3,120 ohms, RS 2  is 8,120 ohms, RP 1  is 2,378 ohms, RP 2  is 4,481 ohms, and Vout is 3.561 volts.  FIG. 4  assumes ideal resistances. In practice, the resistors R 1  through R 15  may not be at the exact resistances illustrated in  FIG. 2 . As described in more detail below, the switching device allows for a certain amount of resistance error tolerance. The resistance error tolerance may be governed by the number of switches included in the switching device, and the resolution of the A/D converter  104 . 
         [0034]    With reference to  FIG. 5 , a conversion table for an A/D converter  104  operating in a “normal mode” is shown. As described in more detail below, the A/D converter  104  may also be operated in a “stuck key” mode. In normal mode, voltage ranges are associated with each of the switches SW 1  through SW 12  as well as a “dead-band”. The dead-band corresponds with the Vout when all of the switches are open. 
         [0035]    As shown in  FIG. 5 , the A/D converter compares Vout with a number of Vout ranges. The Vout ranges allow for resistance error. Tolerances may be specified for the resistors R 1  through R 15 . The resistance of R 1  and R 13  may be accurate to within a tolerance of five percent of the resistances specified by  FIG. 2 . The resistance of the remaining resistors may be accurate to within a tolerance of one percent of the resistance specified by  FIG. 2 . 
         [0036]    Operating in normal mode, the AND converter  104  receives Vout from the switching device  100  and outputs a digital signal corresponding to the specified Vout voltage range. As shown in  FIG. 5 , when the Vout received by the A/D converter  104  falls between 3.536 volts and 3.585 volts, the A/D converter  104  outputs a digital signal corresponding to SW 4 . When the Vout received by the A/D converter  104  falls between 2.698 volts and 2.752 volts, i.e., the dead-band, the A/D converter  104  outputs a digital signal indicating that all switches are open. 
         [0037]    The A/D converter  104  may accomplish an analog-to-digital conversion by way of a volts-per-bit calculation. The A/D converter  104  may output a 10 bit digital signal. The A/D converter  104  may use a volts-per-bit constant, such as 0.00532227 volts-per-bit. When the A/D converter  104  receives a Vout of 3.561 volts, the A/D converter  104  may calculate a corresponding bit output of 669 (base-10), or 1010011101 (binary). As can be appreciated, other bit resolutions for the A/D converter  104 , and other methods of analog-to-digital conversion may be used. 
         [0038]    With reference to  FIG. 6 , a graph illustrates Vout when each of switches SW 1  through SW  12  is closed. Additionally, the dead-band is illustrated. The dead-band falls between the Vout corresponding with closure of switches SW 6  and SW 7 . 
         [0039]    The switching device  100  includes two critical switches, SW 1  and SW 12 . The closure of the critical switches is recognized even when one of the non-critical switches is stuck closed. With reference to  FIGS. 7 and 8 , Vout is shown when each of switches SW 2  through SW 11  is stuck closed and when SW 1  and SW 12  are closed. When SW 4  is stuck closed, and no other switches are closed, Vout will remain at 3.561 volts, as shown in  FIG. 4 . In the traditional switching system, the device would now be inoperable with the switch stuck closed. No other switch closures would be recognizable. 
         [0040]    As shown in  FIGS. 7 and 8 , when any of keys SW 2  through SW 11  are stuck closed, closure of SW 1  and SW 12  are still recognized. In the above example, when SW 4  is stuck closed, closing SW 1  causes Vout to change to 5.31 volts. Likewise, when SW 4  is stuck closed, closing SW 12  causes Vout to change to 0.22 volts. 
         [0041]    When any of switches SW 2  though SW 11  are stuck closed, the control module  110  may recognize the sustained Vout, and may enter stuck switch mode. As shown in  FIG. 9 , in stuck switch mode, the Vout ranges for SW 1  and SW 12  are widened. For SW 1 , a Vout of between 4.800 volts and 5.337 volts is recognized as an SW 1  closure. For SW 12 , a Vout of between 0.113 volts and 0.630 volts is recognized as an SW 12  closure. 
         [0042]    Continuing with the above example, when SW 4  is stuck closed, closing SW  1  causes Vout to change to 5.31 volts and closing SW 12  causes Vout to change to 0.22 volts. As shown in  FIG. 9 , these are recognized as SW 1  and SW 12  closures, respectively. 
         [0043]    In this way, even when a non-critical switch, such as SW 2  through SW 11 , is stuck closed, the control module is able to recognize closure of a critical switch, such as SW 1  or SW 12 . The critical switches may correspond with certain critical functions such as “power off” or “pause”. For example, in an appliance such as a dishwasher, the user may be able to turn the dishwasher off, or pause a dishwasher cycle, regardless of whether one of the other input keys is malfunctioning and stuck. 
         [0044]    When one of the critical switches becomes stuck, the control module  110  simply shuts down the controlled device. If, for example, the “pause” button on the dishwasher becomes stuck, the control module  100  simply shuts the dishwasher off until the stuck switch condition is repaired. 
         [0045]    With reference to  FIG. 10 , a control algorithm  1000  for a controlled device with a switching device  100  is shown. The control module  110  and A/D converter  104  execute the control algorithm  1000 . Control begins in step  1002 . In step  1004 , the analog Vout is received from the switching device  100 . In step  1006 , Vout is compared with previous Vout(s). If Vout has remained the same for a predetermined time, a stuck switch condition may exist. In step  1008 , the control module  110  determines whether a stuck switch condition exists, based on the comparison made in step  1006 . 
         [0046]    When a stuck switch condition does not exist, a normal mode A/D conversion of Vout is performed in step  1010 . The normal mode conversion is made according to the table depicted in  FIG. 5 . Control proceeds to step  1004 . Operation continues and the next analog Vout is received in step  1004 . 
         [0047]    In step  1008 , when a stuck switch condition exists, control proceeds to step  1012 . In step  1012 , the control module  110  determines whether the stuck switch is a stuck critical switch. When the stuck switch is a stuck critical switch, control proceeds to step  1014  and shuts down the controlled device, such as the appliance, and ends in step  1016 . 
         [0048]    In step  1012 , when the stuck switch is not a critical switch, a stuck switch mode AND conversion is performed in step  1018 . The stuck switch mode AND conversion is made according to the table depicted in  FIG. 9 . In stuck switch mode, the control module  110  and A/D converter  104  detect only critical switch closures. Voltages corresponding with other non-critical switch closures are ignored. Control then loops back to step  1004  and the algorithm  1000  is started anew. 
         [0049]    When the stuck switch becomes un-stuck, the control module  110  and A/D converter  104  perform normal mode AND conversion of Vout once again in step  1010 . When the stuck switch remains stuck, the control module waits for closure of a critical switch by performing the stuck switch mode A/D conversion in step  1018 . 
         [0050]    In this way, a controlled device configured with the switching device  100  according to the present teaching is able to receive critical switch input regardless of whether the non-critical keys are pressed or stuck. The switching device allows the controlled device to continue functioning during a partial malfunction such as a stuck key. Additionally, the switching device with critical keys may be used to facilitate certain special functions. For example, by pressing a critical key in combination with another non-critical key, the control module may enter a special mode, such as a safety, setup, or lock-out mode. 
         [0051]    Referring now to  FIG. 11 , the switching device, the A/D converter, and the control module may be hosted on more than one IC. The critical resistors, R 14  and R 15 , may be contained on different IC&#39;s. For example, the switches SW 1  through SW 12  and resistor R 15  may be contained on a first IC  150  along with a user display device  120  and a keyboard device  122 . The A/D converter  104 , control module  110 , and resistors R 1  through R 14  may be contained on a second IC  152 . The first IC  150  and the second IC  152  may be connected by a ribbon cable  154  or other suitable electrical connection device. The first IC  150  may be located such that the keyboard  122  and the user display  120  are easily accessible and viewable by the user. The second IC  152  may be located elsewhere. The control module  110  may include a processor, random access memory (RAM), and read only memory (ROM), as well as other electronic components necessary for operation of the device. Thus, the second IC  152  may be located in a housing located elsewhere on the appliance. For example, the second IC  152  may be located to allow sufficient cooling of the processor. 
         [0052]    In a multiple IC board implementation, the IC boards may become disconnected. In such case, the keyboard  122  and user display  120  may become disconnected from the A/D converter  104  and control module  110 . In the traditional system, when the IC&#39;s become disconnected, Vout either pulls to zero volts or Vcc, and the A/D converter  104  treats the received Vout as if no user input has been received. In other words, the traditional system continues operation when the IC&#39;s have become disconnected and the keyboard  122  is no longer connected to the A/D converter  104  and control module  110 . 
         [0053]    When the first IC  150  and the second IC  152  of the present teachings are disconnected, however, the control module  110  halts operation of the controlled device. When resistors R 14  and R 15  are located on separate IC boards, and when the IC boards become disconnected, Vout pulls to either zero volts or Vcc. In such case, the A/D converter  104  and control module  110  read the Vout as a stuck critical switch. 
         [0054]    As shown in  FIG. 10 , when a stuck critical switch is detected, the control module  110  shuts down the controlled device. In other words, a disconnected keyboard condition is treated in the same manner as a stuck critical key condition. In both cases, the fault causes the control module  110  to halt operation and shut down the controlled device, such as the appliance. 
         [0055]    While the exemplary embodiment of a switching device has been described above with a specific configuration, this system may be constructed with many different configurations and components as necessary or desired for a particular application. The above configurations and components are presented only to describe one particular embodiment and should be viewed as illustrating, rather than limiting, the present teachings. Thus, the description is merely exemplary in nature and variations that do not depart from the gist of the present teachings are intended to be within the scope of the teachings. Such variations are not to be regarded as a departure from the spirit and scope of the present teachings.