A low-cost microcontroller-based interface circuit for capacitive sensors insensitive to shunting conductance effects

This paper proposes a simple and low-cost interface circuit for capacitive sensors that is insensitive to the parasitic conductance (G(x)) of the sensor. Such a circuit relies on a previous circuit also proposed by the authors, in which the sensor is directly connected to a microcontroller without using analog circuitry between them. The novel circuit uses the same hardware, but it performs an additional measurement and executes a new calibration technique to compensate for the effects of G(x). Experimental results show an error due to the parasitic conductance of 0.4 % for G(x) = 100 nS and 3 % for G(x) = 450 nS, which are more than ten times smaller than those obtained without the improvements proposed herein.