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

Abstract

This paper proposes a simple and low-cost interface circuit for capacitive sensors that is insensitive to the parasitic conductance (G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> . Experimental results show an error due to the parasitic conductance of 0.4 % for G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> =100 nS and 3 % for G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> =450 nS, which are more than ten times smaller than those obtained without the improvements proposed herein.