Non-contact capacitive sensing system for use in toys

Abstract

For toys that respond to touch to trigger a particular response, an activation system utilizes a non-contact capacitive proximity sensing system that permits activation when a finger, lips or other body part is close to a sensing area in the form of a hidden flat conductor under the surface of a toy so that actual touching of the sensor is not required to activate any of the functions of the toy. Low capacitance coaxial cable buried in the toy is used to connect the sensing area to the capacitance detection circuit so that only the capacitance of the sensing area is measured. Proximity sensing activation occurs when there is an increase in capacitance at the sensing area due to the proximity of a body part, with the change in capacitance being detected through the use of an RC circuit in the feedback loop of an oscillator whose frequency decreases when sensed capacitance increases. Self-calibrating techniques involving adaptive threshold adjustment provide for fail safe sensing in all environments and across unit-to-unit component variations, with the thresholds being set each time the toy is turned on, then adjusted over time as necessary. In one embodiment, multiple sensing areas are sequentially addressed through a multiplexing circuit and all audio circuitry is turned off during sensing to prevent capacitance sensing errors.

What is claimed is:  
     
         1 . In a battery-operated toy, a system for sensing the proximity of a human body part to a sensing area at said toy for the activation of a selected toy response, comprising: 
 A non-contact capacitance sensing unit within said toy including an electrically conductive sensing pad, a proximity sensing circuit for the activation of said toy response and a means for connecting said pad to said proximity sensing circuit, whereby said pad may be buried beneath the outer covering of said toy to avoid unsightly visible activation apparatus.    
     
     
         2 . The system of  claim 1 , wherein said means for connecting said pad to said proximity sensing circuit includes a shielded conductor, whereby capacitance sensing is localized to changes in capacitance at said pad.  
     
     
         3 . The system of  claim 1 , wherein said toy includes multiple pads distributed about said toy and wherein said proximity sensing circuit includes a multiplexer for sequentially accessing said pads.  
     
     
         4 . The system of  claim 1 , and further including an automatic calibrating unit for sensing capacitances absent the proximity of a body part and for setting a corresponding capacitance threshold level, the calibrating unit being self-adaptive.  
     
     
         5 . The system of  claim 4 , wherein said proximity sensing circuit includes an RC-controlled oscillator and a counter coupled thereto, the frequency of said oscillator being inversely proportional to the capacitance associated with said pad, and wherein said automatic calibrating unit has said corresponding capacitance threshold level established by the count in said counter.  
     
     
         6 . The system of  claim 1 , wherein said selected toy response is a predetermined sound, and wherein said toy has a sound generator for generating said predetermined sound when activated by said toy, and further including means for inhibiting said proximity sensing circuit when said sound generator is activated, thereby to eliminate any false readings of capacitance due to the electrical noise of said sound generator during capacitance sensing.  
     
     
         7 . The system of  claim 4 , wherein said calibrating unit is activated when said toy is turned on to establish said capacitance threshold level.  
     
     
         8 . The system of  claim 5 , wherein said calibrating unit includes means for adaptively setting said capacitance threshold level.  
     
     
         9 . The system of  claim 8 , wherein said means for adaptively setting said capacitance threshold level includes a unit for setting said capacitance threshold level to a maximum value, means for taking a current capacitance reading, means for ascertaining if the current capacitance reading is less than said threshold and means responsive thereto for saving the current capacitance as the new threshold level.  
     
     
         10 . The system of  claim 9  and further including means for establishing if the current capacitance reading is larger than said threshold by a predetermined margin and for activating said toy response responsive thereto.  
     
     
         11 . A non-contact capacitance sensing system, comprising: 
 an electrically conductive patch;    a length of coaxial cable having a center conductor coupled to said conductive patch;    an RC-controlled oscillator coupled to said coaxial cable and having an output frequency inversely proportional to the capacitance associated with said patch;    a counter coupled to the output of said oscillator; and    a threshold circuit coupled to the output of said counter for indicating the presence of a body part adjacent to said patch when the count from said counter varies from said threshold, whereby the adjacency of said body part to said patch is sensed.    
     
     
         12 . Apparatus for triggering a predetermined response in a toy, comprising: 
 a non-contact capacitive proximity system having a conductive pad for sensing the proximity of a body part adjacent said pad; and,    a threshold circuit for generating a trigger when the proximity of a body part is sensed.    
     
     
         13 . The apparatus of  claim 12 , wherein the threshold set by said thresholding circuit is adaptively set.  
     
     
         14 . The apparatus of  claim 13 , wherein said adaptively set threshold is set when said toy is turned on.  
     
     
         15 . The apparatus of  claim 14 , wherein said adaptively set threshold is further adjusted after the original setting when said toy is turned on.  
     
     
         16 . The apparatus of  claim 15 , wherein capacitances associated with said pad are periodically monitored, with said threshold being adaptively set when sensed capacitance associated with said pad is sufficiently different from a previously established threshold.  
     
     
         17 . The apparatus of  claim 16 , wherein said threshold is reset if the current sensed capacitance is lower than that associated with said threshold, whereby a capacitance threshold that is set during the proximity of a body part is adjusted upon removal from proximity of said body part from said pad.