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 .