Abstract:
Method and apparatus for monitoring wet contact touchpads where the opening of the contacts and the closing of the contacts of a wet contact touchpad are monitored and sensed by a timer/controller. The wet contact touchpad forms a capacitor which is charged to maintain a low voltage when the contacts are open. Upon reaching a predetermined decreasing voltage charge across the wet contact touchpad, the voltage status is further scrutinized by voltage sampling to determine when a contact closure or a contact break has occurred. Such determination is carried out in multiple cycle fashion by quickly and repeatedly introducing a charge voltage, discontinuing the charge voltage, and sampling the charged voltage to determine a decrease or an increase. A decrease indicates a wet contact touchpad closed circuit and an increase indicates a wet contact touchpad open circuit. Sampling of the increasing or decreasing charges determines timed occurrences accurately.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   None. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is for a sports timing device and, more particularly, for a method and apparatus for monitoring wet contact touchpads in a swim timing system that allows accurate detection of both the actuation of and the release of a switch-like wet contact touchpad while preventing corrosion of the switch contact material. More particularly, the wet contact touchpads consist of flexible metal electrode plates separated by non-conducting spacers forming a simple switch. The space between the flexible metal electrode plates is allowed to fill with water when the wet contact touchpad is placed in a pool. The large parallel flexible metal electrode plates separated by water form a large capacitor which must be charged up by the monitoring circuit before a switch closure can be sensed. The potential across the plates must not exceed the ionization voltage of water (˜1.3V) or corrosion will occur. 
   2. Description of the Prior Art 
   In prior art devices, the capacitance formed by the opposing flexible metal electrode plates of a wet contact touchpad does not present a significant problem if only closures need to be monitored because the voltage across the plates will change rapidly when they are shorted together. Accurately detecting the release is more difficult. A wet contact touchpad can be modeled as a large capacitor in series with a small resistor. A common charging method is to pull one flexible metal electrode plate of the wet contact touchpad up to a voltage less than 1.3V, which results in a series RC circuit where the voltage across the capacitor formed by the flexible metal electrode plates is an exponential function of time. The large wet contact touchpad capacitance makes the time constant of this circuit too large to allow accurate sensing of the release. 
   Directly monitoring the voltage across the wet contact touchpad while charging is impractical because of the series resistance in the wet contact touchpad model. The voltage across the capacitor plus the voltage drop across the resistor will always equal the full charging voltage. In addition, the capacitance and the resistance in the wet contact touchpad model are not fixed and may vary depending on wet contact touchpad age, size, and pool chemistry, which makes simple level detector circuits inadequate. 
   SUMMARY OF THE INVENTION 
   The present invention utilizes a sensing and switching approach method and apparatus to accurately detect the touch and the release of a wet contact touchpad by sampling rates of decreasing or increasing voltage sampled between rapidly occurring charging cycles. To foster accuracy and to provide an adequate number of samples, the time required to charge the wet contact touchpad is reduced by charging with a significant level of high voltage, thereby reaching the charge-up voltage with a minimum amount of time. The charging circuit is then electronically disconnected when the wet contact touchpad reaches a desired voltage charge. This is accomplished using a microcontroller interfaced to an analog-to-digital converter (ADC) for monitoring the voltage, and a transistor switch arrangement to control the charging circuit. The microcontroller continually samples the wet contact touchpad charge voltage through the ADC, and signals a “touch” when n number of decreasing voltage samples in a row are detected. The microcontroller then switches the charging circuit on in preparation for sensing the release. 
   The problem with the wet contact touchpad series resistance is solved by switching the charging circuit off before sampling the voltage. With no charging current through the internal resistance, there will be no voltage drop across it, and the voltage across the capacitance can be sampled. This process repeats: turn charger on, turn charger off; sample, turn charger on . . . etc. Successive samples are compared, and n number of increasing samples in a row indicate that the wet contact touchpad is released and is charging back up. The microcontroller continues this charge/sample cycle until the wet contact touchpad is completely charged. If the sample rate is fast enough, small changes of the resistance and capacitance will not significantly affect the accuracy of this method. This is because differences between samples are compared, rather than comparing each sample to a fixed threshold. 
   There is also another possibility for even more accurate sensing using a variation of this method and a little more mathematical processing. From the samples taken during the charging of the wet contact touchpad, the RC time constant of the circuit could be calculated (approximated). The time constant and the present voltage level could then be used to calculate how long the wet contact touchpad had been charging. Subtracting this amount of time from the present time would yield the time at which the release occurred. 
   One significant aspect and feature of the present invention is a method and apparatus for accurately detecting the touching and releasing of a wet contact touchpad. 
   Another significant aspect and feature of the present invention is a method and apparatus for accurately monitoring the state of voltage charge of a wet contact touchpad. 
   A further significant aspect and feature of the present invention is a method and apparatus for accurately detecting the touching of a wet contact pad when n number of decreasing voltage samples in a row are sensed. 
   A further significant aspect and feature of the present invention is a method and apparatus for accurately detecting the release of a wet contact pad when n number of increasing voltage samples in a row are sensed. 
   Still another significant aspect and feature of the present invention is a method and apparatus for accurately detecting reaction time between a signaled start involving the reaction time between constant or near constant touching of a wet contact touchpad and release of the wet contact switch. 
   Yet another significant aspect and feature of the present invention is a method and apparatus for accurately detecting the touching and releasing of a wet contact touchpad whereby a suitable non-corrosive low voltage is incorporated to promote accuracy and long life of the wet contact touchpads. 
   Having thus mentioned certain significant aspects and features, or described embodiments, of the present invention, it is the principal object of the present invention to provide a method and apparatus for accurately detecting the touching and releasing of flexible metal electrode plates of a wet contact touchpad and for the prevention of corrosive forces upon the flexible metal electrode plates of a wet contact touchpad. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
       FIG. 1  is an isometric view of the apparatus for monitoring wet contact touchpads, the present invention, shown in electrical connection with and in use with a wet contact touchpad, a horn start system, and an external start horn; 
       FIG. 2  is a cross section view of the wet contact touchpad along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  illustrates the alignment of  FIG. 4   a  with respect to  FIG. 4   b;    
       FIGS. 4   a  and  4   b  together represent an electrical schematic of the timer/controller, the present invention, connected to a wet contact touchpad and to a start system; 
       FIG. 5  is block diagram showing a wet contact touchpad model; and, 
       FIG. 6  illustrates the operation of the timer/controller shown in  FIGS. 4   a  and  4   b  as witnessed on an oscilloscope. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is an isometric view of the apparatus for monitoring wet contact touchpads  10 , the present invention, shown in electrical connection with and in use with a wet contact touchpad  11 , a horn start system  12 , and an external start horn  13 . A suitably housed timer/controller  14  includes, but is not limited to, an electronic display  16 , which could be any suitable numerical display, such as a liquid crystal display, an LED or the like, a microcontroller  18 , paired START jacks  20 , paired STOP jacks  22 , paired RESET jacks  24 , paired HORN jacks  26 , switches connected to the above jacks including a start switch  28 , a stop switch  30 , a reset switch  32  and a horn switch  34 , respectively, and plugs which can connect to the above jacks including a start plug  36 , a stop plug  38 , a reset plug  40  and a horn plug  42 . The wet contact touchpad  11  can include opposing front and rear panels  44  and  46  of flexible non-conducting material, such as plastic, having one or more opposing flexible metal electrode plates  48  and  50  and opposing flexible metal electrode plates  52  and  54  located, respectively as illustrated, on the interior faces of the opposing non-conducting front and rear panels  44  and  46 . A plurality of non-conducting separators  56   a – 56   n  ( FIG. 2 ), which could be foam, distance the front and rear panels  44  and  46  and, thus, the opposing flexible metal electrode plates  48  and  50  and opposing flexible metal electrode plates  52  and  54 , thereby forming a capacitor which is submersible. 
     FIG. 2  is a cross section view of the wet contact touchpad  11  along line  2 — 2  of  FIG. 1 . Shown in particular is the location of several of the opposing non-conducting separators  56   a – 56   n  which separate the non-conducting front panel  44  and the non-conducting rear panel  46  and, thus, the flexible metal electrode plates  48  and  50  (and  52  and  54 ). The space  57  between the flexible metal electrode plates  48  and  50  (and flexible metal electrode plates  52  and  54 ) is allowed to fill with water, which is a dielectric. The flexible metal electrode plate pairs  48  and  50  and  52  and  54  are separated by the water (dielectric) and therewith form a large capacitor. Also shown is a connection cable  58  connected across the flexible metal electrode plates  48  and  50 . The pairs of flexible metal electrode plates  48  and  50  and  52  and  54  are interconnected, such as is shown in  FIG. 1 . 
     FIG. 3  illustrates the alignment of  FIG. 4   a  with respect to  FIG. 4   b.    
     FIGS. 4   a  and  4   b  together represent an electrical schematic of the timer/controller  14 , the present invention, connected to the wet contact touchpad  11  and to the horn start system  12  including the external start horn  13 . With respect to monitoring the wet contact touchpad  11 , the most pertinent part of the electrical schematic is the circuit connected to the STOP input jack  22 . The three other sets of jacks have low voltage switch input jacks that are also monitored, and all the jacks use the A/D converters  59   a – 59   d  located internally in the microcontroller  18 , but are not capable of sensing the release of a wet contact touchpad  11 . The START input jack  20  is used to start an internal timer residing in the microcontroller  18 . The function of the STOP input jack  22  is determined by the operating mode of the microcontroller  18 , and the STOP input jack  22  can be connected to a touchpad, such as the wet contact touchpad  11 , or to a simple external switch (not shown). The function of the HORN input jack  26  is also determined by the operating mode of the internal timer. The HORN input jack  26  may be connected to a take-off platform sensor (start reaction timing), or may be used to sound a horn when the switch  34  is closed. The RESET input jack  24  is used to reset the internal timer to zero in preparation for another timing event. 
   Shown in particular is a charging circuit  60  connected to the microcontroller  18 . The microcontroller  18 , with other components, monitors the status of the wet contact touchpad  11 , samples and controls other aspects related to the wet contact touchpad  11 , and is connected to the wet contact touchpad  11  by the STOP jack  22 . The microcontroller  18  causes measured timed periods for an event or occurrence to be outputted by the display  16 . Also shown in particular is the charging circuit  60  connected by the STOP jack pair  22  to, but not at all times, electrically influence the wet contact touchpad  11 . The charging circuit  60 , which also functions as a charging current switch, includes power transistors  62  and  64  and resistors  66 ,  68  and  70   a – 70   n . The output of the charging circuit  60  is controlled by the microcontroller  18  to either provide or not provide charging current to the wet contact touchpad  11 , as explained later in detail. In the STOP circuit, a diode  72  provides a low impedance path for the charging current from the charging circuit  60  out to the wet contact touchpad  11 , while blocking any signal that a user may inadvertently connect to the input at the STOP jack  22 . Resistor  74  allows the voltage on each side of the diode  72  to equalize, while still maintaining a high impedance to any signal the user may connect. A zener diode clamp  73  prevents the voltage from exceeding a predetermined value, which could damage the inputs of the microcontroller  18 . Transient voltage surge suppressors  75   a – 75   n  are incorporated as protective devices across the leads from the circuitry connecting the START jack  20 , the STOP jack  22 , the RESET jack  24  and the HORN jack  26  to quickly react to voltage spikes by shunting any spikes to ground to avoid damaging the inputs of the microcontroller  18 . The overall circuit can function satisfactorily without the transient voltage surge suppressors  75   a – 75   n , but with the transient voltage surge suppressors  75   a – 75   n , additional protection is provided in the event the current switching circuit (charging circuit  60 ) or external devices connected to the STOP input jack  22  or the other inputs produce transients that occur faster than the protection offered by the zener diode clamp  73 . 
     FIG. 5  is a block diagram of a prior art system involving a wet contact touchpad model and a microcontroller which activates an electrically connected starting signal, which may be visual and/or aural to start a swimming race and then measures the time involved until a swimmer touches the wet contact touchpad to signal the end of the race. In this prior art system, voltage across the wet contact touchpad is drawn down and sensed by a microprocessor, whereupon the elapsed time is displayed. Such system does not require fast recharging of the electrode plates of the wet contact touchpad, as only the end of a timed event is sensed. The capacitance found in many wet contact touchpads is on the order of 0.04F and the resistance can be approximated at 1 ohm. Using this as an example in the wet contact touchpad model, and using the 5RC approximation, it will take approximately 0.2 second to charge the capacitor up to full supply voltage (assuming that the output resistance of the charging circuit  60  is zero). In this regime, sensing of contact release of the wet contact touchpad is neither important nor supported. However, in the instant invention, other useful data can be obtained. For example, data referencing starting reaction time can be obtained, such being useful for training or for analyzing a swimmer&#39;s ability to quickly leave a starting mark or area. Also, data relating to actual away from the mark and return to the mark elapsed time without reference to or use of a visual or aural starting signal can be measured and displayed. Such sensing and display can require time sampling at a greater occurrence level where a new charge-up time significantly less than 0.2 second is desired. The charge-up time can be shortened significantly by quickly charging the capacitor (wet contact touchpad) by the use of a charging circuit controlled by a microcontroller to charge the wet contact touchpad from a higher than normal voltage supply, such as 16 volts for example, and by then turning the charging circuit off when the wet contact touchpad reaches a desired voltage, such as 0.25 volt. The RC constant of the circuit is still the same, but because the supply voltage is much higher than the desired charge voltage, the time to charge the wet contact touchpad to 0.25 volt is significantly shortened, thus leaving non-charging gaps for sampling. The wet contact touchpad voltage cannot be measured accurately while charging because the charging current through the resistance of the wet contact touchpad model causes a voltage drop which, when added to the voltage across the capacitance, will always be equal to the supply voltage. As such, this is recognized, and the charging circuit is turned off before measuring of the wet contact touchpad voltage occurs. 
     FIG. 6  illustrates the operation of the timer/controller  14  shown in  FIGS. 4   a – 4   b , as may be witnessed on an oscilloscope. The top trace  76 , including trace reference points or regions  76   a – 76   n , indicates the voltage across the wet contact touchpad  11 , and the bottom trace  77  indicates the output from the microcontroller  18 , showing at  78  when the wet contact touchpad  11  is sensed as being in open status (output low) or at  80  when the wet contact touchpad  11  is sensed as being in closed status (output high). With the wet contact touchpad  11  open and fully charged, 0.25V is indicated at trace reference region  76   a . At trace reference region  76   b , decreasing voltage is sensed by the microcontroller  18 , and the microcontroller  18  starts numerous charge/sample cycles (trace reference region  76   c ) where a high voltage charge is applied by the charging circuit  60  of the timer/controller  14  and, subsequently, is cut off at a desired voltage to allow interspersed voltage samplings free from the influence of charging. When n-consecutive samples of decreasing voltage (trace reference region  76   d ) are recognized by the microcontroller  18 , the microcontroller  18  output indicates closed status, as indicated at  80 , and initiates a signal based on “closure” to start timing for readout on the display  16 . Such closed status, as indicated at  80 , will continue until n-consecutive samples of increasing voltage occur. Accordingly, decreasing or steady voltage samples (trace reference region  76   e ) are monitored by the microcontroller  16  with no change of the closed status, as indicated at  80 , to the open status, as indicated at  78 . When n-consecutive samples of increasing voltage (trace reference region  76   f ) are recognized by the microcontroller  18 , the microcontroller  18  output indicates open status, as indicated at  78 , and initiates a signal based on “open” to terminate timing for readout on the display  16 . Charge/sample cycles continue until a suitable voltage of at least or just slightly more than 0.25V (trace reference region  76   a  again) is attained, whereupon the charge/sample cycles cease, having reached a suitable charge state. The wet contact touchpad  11  can exhibit a certain amount of “leakage”; i.e., it will not retain a charge indefinitely even without being pressed. For this reason, the microcontroller  18  must be able to determine whether a drop in wet contact touchpad  11  voltage is due to leakage or due to a touch. This is accomplished by cycling the charging circuit  60  on and off twice (trace reference region  76   n ) and comparing the voltage samples taken after each charging cycle. If the samples are of increasing voltage, the wet contact touchpad  11  is not closed and the wet contact touchpad  11  needs to be recharged to compensate for leakage. If the two samples are decreasing, then the wet contact touchpad  11  is closed and timing functions are initiated. 
   Mode of Operation 
   The mode of operation of the apparatus for monitoring wet contact touchpads and the method for monitoring wet contact touchpads are best described in detail by reference to the previously described figures followed by a practical use example, which is now described. The timer/controller  14  utilizes four digits in the display  16  for displaying times, an internal horn (not shown), and four jack inputs  20 ,  22 ,  24  and  26 , each paralleled with a switch, to facilitate the connection of external switches, start systems, touchpads, take-off platform sensors, etc. The timer/controller  14  has multiple modes of operation which can be set or influenced using the switches  28 ,  30 ,  32  and  34 . One area of usefulness of the present invention that applies to the touchpad monitoring circuit, as found in the timer/controller  14 , is the ability to measure start reaction time, such as in the backstroke. The timer/controller  14  starts timing when the START circuit is activated, such as by the horn start system  12 , where the START jack  20  would normally be connected to a horn start system  12  which sounds a start tone through the start horn  13  and optionally causes a strobe to flash when the official starts the race. A set of relay contacts in the horn start system  12  is connected through a cable to the START jack  20  of the timer/controller  14 . An alternate method of starting the timing could be by the closure of the start switch  28  which is in parallel with the start jack  20 . 
   In a backstroke race, the swimmers start in the water by placing their feet against wet contact touchpads  11  and holding the starting block (or pool gutter) with their hands. When the swimmers place their feet against the wet contact touchpads  11 , the flexible metal electrode plates  48  and  50  and  52  and  54  are forced into intimate contact, thereby causing sensing by the timer/controller  14 . When the swimmers hear the start signal, they push off and the contacts of the wet contact touchpads separate. A swimmer may move his feet on the touchpad and cause multiple cycles of the wet contact touchpad  11 , so the timer/controller  14  monitors the cycles and uses the last opening of the contacts of the wet contact touchpad  11  after the start to stop the timing. The time between the START input and the last opening of the STOP input is the start reaction time, which is then displayed on the display  16 . Alternatively, total elapsed time could be accurately determined without the use of a starting signal by determination by the timer/controller  14  of the time between the opening of the contacts of the wet contact touchpad  11  (departure from the wet contact touchpad  11 ) and the closure of the contacts of the wet contact touchpad  11  (return touching of the wet contact touchpad  11 ). 
   Various modifications can be made to the present invention without departing from the apparent scope thereof. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               PARTS LIST 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
               10 
               apparatus for 
             
             
                 
                 
               monitoring wet 
             
             
                 
                 
               contact touchpads 
             
             
                 
               11 
               wet contact 
             
             
                 
                 
               touchpad 
             
             
                 
               12 
               horn start system 
             
             
                 
               13 
               start horn 
             
             
                 
               14 
               timer/controller 
             
             
                 
               16 
               display 
             
             
                 
               18 
               microcontroller 
             
             
                 
               20 
               start jack 
             
             
                 
               22 
               stop jack 
             
             
                 
               24 
               reset jack 
             
             
                 
               26 
               horn jack 
             
             
                 
               28 
               start switch 
             
             
                 
               30 
               stop switch 
             
             
                 
               32 
               reset switch 
             
             
                 
               34 
               horn switch 
             
             
                 
               36 
               start plug 
             
             
                 
               38 
               stop plug 
             
             
                 
               40 
               reset plug 
             
             
                 
               42 
               horn plug 
             
             
                 
               44 
               front panel 
             
             
                 
               46 
               rear panel 
             
             
                 
               48 
               flexible metal 
             
             
                 
                 
               electrode plate 
             
             
                 
               50 
               flexible metal 
             
             
                 
                 
               electrode plate 
             
             
                 
               52 
               flexible metal 
             
             
                 
                 
               electrode plate 
             
             
                 
               54 
               flexible metal 
             
             
                 
                 
               electrode plate 
             
             
                 
               56a–n 
               non-conducting 
             
             
                 
                 
               separators 
             
             
                 
               57 
               space 
             
             
                 
               58 
               connection cable 
             
             
                 
               59a–n 
               A/D converters 
             
             
                 
               60 
               charging circuit 
             
             
                 
               62 
               transistor 
             
             
                 
               64 
               transistor 
             
             
                 
               66 
               resistor 
             
             
                 
               68 
               resistor 
             
             
                 
               70a–n 
               resistors 
             
             
                 
               72 
               diode 
             
             
                 
               73 
               zener diode clamp 
             
             
                 
               74 
               resistor 
             
             
                 
               75a–n 
               transient voltage 
             
             
                 
                 
               surge suppressors 
             
             
                 
               76 
               top trace 
             
             
                 
               76a 
               trace reference 
             
             
                 
                 
               region (full 
             
             
                 
                 
               charge) 
             
             
                 
               76b 
               trace reference 
             
             
                 
                 
               region 
             
             
                 
                 
               (decreasing 
             
             
                 
                 
               voltage) 
             
             
                 
               76c 
               trace reference 
             
             
                 
                 
               region (charge 
             
             
                 
                 
               sample cycles) 
             
             
                 
               76d 
               trace reference 
             
             
                 
                 
               region 
             
             
                 
                 
               (decreasing 
             
             
                 
                 
               voltage) 
             
             
                 
               76e 
               trace reference 
             
             
                 
                 
               region 
             
             
                 
                 
               (decreasing or 
             
             
                 
                 
               steady voltage) 
             
             
                 
               76f 
               trace reference 
             
             
                 
                 
               region 
             
             
                 
                 
               (increasing 
             
             
                 
                 
               voltage) 
             
             
                 
               76n 
               trace reference 
             
             
                 
                 
               region (cycling 
             
             
                 
                 
               on and off twice) 
             
             
                 
               77 
               bottom trace 
             
             
                 
               78 
               open status 
             
             
                 
               80 
               closed status