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This paper proposes a simple and low-cost interface circuit for capacitive sensors that is insensitive to the parasitic conductance (Gx) 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 Gx. Experimental results show an error due to the parasitic conductance of 0.4 % for Gx=100 nS and 3 % for Gx=450 nS, which are more than ten times smaller than those obtained without the improvements proposed herein.