Patent ID: 8089461

Claim:
A system comprising: a capacitance measurement circuit that includes only one capacitance sensor, wherein the capacitance sensor comprises a first conductive strip positioned adjacent to an interior surface of a casing of a device, beneath an area of an external surface of the casing touched by a user, wherein the conductive strip forms a capacitor, a capacitance of which is increased when the user touches the exterior surface of the casing; a switch coupled to the capacitor, the switch to alternately couple the capacitor to a voltage source to charge the capacitor and to a ground supply to discharge the capacitor; a detector circuit coupled to the capacitor, the detector circuit to determine when the capacitor reaches a pre-set charge and when the capacitor is fully discharged; a control circuit coupled to the detector circuit, the control circuit responsive to the detector circuit to alter a position of the switch, wherein the position is altered when the capacitor reaches the pre-set charge and when the capacitor is fully discharged; a counter coupled to the control circuit, the counter to count a number of times the position of the switch is altered in a pre-established period of time and compare the number of times the position of the switch is altered to a pre-established count value; and a signal generator circuit coupled to the counter, the signal generator circuit to generate a signal to wake the device from a sleep state if the number of times the position of the switch is altered does not match the pre-established count value during the pre-established period of time.