Method and Apparatus For Sensing the Force With Which a Button is Pressed

Abstract

An example method includes measuring a capacitance of an actuator and a conductive element when, responsive to a force applied to the actuator, the actuator is coupled to a reference voltage and deformed such that surface area of the actuator proximate to the conductive element increases. The example method includes determining the force applied to the actuator based on the measured capacitance.

What is claimed is: 
     
         1 - 20 . (canceled) 
     
     
         21 . A method comprising:
 measuring a capacitance of an actuator and a conductive element when, responsive to a force applied to the actuator, the actuator:
 couples to a reference voltage; and 
 deforms such that a surface area of the actuator in proximity to the conductive element increases; and 
   determining the force applied to the actuator based on the measured capacitance.   
     
     
         22 . The method of  claim 21 , wherein the measuring of the capacitance includes measuring the capacitance that increases as the surface area of the actuator in proximity to the conductive element increases. 
     
     
         23 . The method of  claim 22 , wherein the measuring of the capacitance includes measuring a maximum capacitance when the surface area of the actuator in proximity to the conductive element is a maximum surface area. 
     
     
         24 . The method of  claim 23 , wherein the determining of the force applied to the actuator, based on the measured capacitance, includes determining a maximum force when the measured capacitance is the maximum capacitance. 
     
     
         25 . The method of  claim 21 , wherein the measuring of the capacitance includes measuring the capacitance when the actuator is deformed in contact with an insulator covering the conductive element and the actuator is coupled with the reference voltage through contact with an uninsulated portion of another conductive element. 
     
     
         26 . The method of  claim 21 , wherein the measuring of the capacitance includes using a relaxation oscillator to measure the capacitance. 
     
     
         27 . The method of  claim 21 , wherein the determining of the force applied to the actuator based on the measured capacitance includes determining the force based on a digital representation of the measured capacitance. 
     
     
         28 . A device comprising:
 a first conductive element coupled with a reference voltage;   a second conductive element covered by an insulator;   an actuator having a conductive surface, wherein responsive to a force applied to the actuator, the actuator configured to:
 couple with the reference voltage through the first conductive element; and 
 deform in contact with the insulator, wherein the deformation of the actuator increases a surface area of the actuator in proximity to the second conductive element; and 
   a circuit configured to measure a capacitance of the second conductive element and the actuator, the circuit including a processing element configured to determine the force applied to the actuator, based on the measured capacitance.   
     
     
         29 . The device of  claim 28 , wherein the capacitance of the second conductive element and the actuator increases as the surface area of the actuator in proximity to the second conductive element increases. 
     
     
         30 . The device of  claim 29 , wherein the surface area of the actuator in proximity to the second conductive element is a maximum surface area when the force applied to the actuator is at a maximum force. 
     
     
         31 . The device of  claim 28 , wherein the actuator is configured to couple with the reference voltage through the first conductive element by contact between the conductive surface of the actuator and an uninsulated portion of the first conductive element. 
     
     
         32 . The device of  claim 31 , wherein the contact between the conductive surface of the actuator and the uninsulated portion of the first conductive element is made prior to the deformation of the actuator in contact with the insulator. 
     
     
         33 . The device of  claim 28 , wherein the reference voltage is a ground voltage. 
     
     
         34 . The device of  claim 28 , wherein the first conductive element is located approximately below a center axis of the actuator, and the second conductive element surrounds the first conductive element. 
     
     
         35 . The device of  claim 28 , wherein the circuit includes a relaxation oscillator to measure a capacitance of the second conductive element and the actuator. 
     
     
         36 . The device of  claim 28 , wherein the processing element is configured to determine the force applied to the actuator, based on a digital representation of the measured capacitance. 
     
     
         37 . A system comprising:
 a printed circuit board comprising:
 a conductive layer covered by an insulating layer; 
 a contact coupled to a ground; 
   a conductive actuator, wherein responsive to a force applied to the conductive actuator, the conductive actuator configured to:
 couple to the ground through the contact; and 
 deform into the insulating layer, wherein the deformation of the conductive actuator increases a surface area of the conductive actuator over the insulating layer and the conductive layer; 
   a measurement device configured to measure a capacitance of the conductive layer and the electrically grounded conductive actuator; and   one or more processors configured to determine the force applied to the electrically grounded conductive actuator, based on the measured capacitance.   
     
     
         38 . The system of  claim 37 , wherein responsive to the force applied to the conductive actuator, the conductive actuator is configured to couple to the ground through an exposed portion of the contact that is not insulated. 
     
     
         39 . The system of the  claim 37 , wherein the conductive layer and the insulating layer at least partially surround the contact. 
     
     
         40 . The system of  claim 37 , wherein the contact is located approximately below a center axis of the conductive actuator.