The figure below shows a Resistor-Capacitor (RC) Decay circuit that conditions a capacitive sensor. The time it takes for the voltage to decay to a threshold is a function of the capacitance, CSEN. A PIC® MCU produces a single-pole step response (voltage) with an RC decay. This circuit measures the decay time where the threshold is proportional to VDD. R1 has a low-temperature coefficient to minimize temperature errors. The PIC MCU provides the switching and control needed.
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