Electronic circuit for the detection of a capacitive variation on two distinct contact capacitors, (C1, C2), comprising means able of squaring the signals generated by a conventional pulse generator and filtered by two filters (R1, C1-R2, C2), wherein the respective capacitors (C1, C2) are the same said contact capacitors which are connected to a respective terminal to a common ground (G); said means are also able to generate respective signals formed of trains of squared pulses, to compare said two signals and to provide an output signal depending on the result of said signals comparison. Said output signal depends on the phase difference between the pulses of said two trains of squared pulses.