Capacitive movement sensor

A relative movement or proximity sensing system has at least one pair of electrodes 52 variations in the capacitance between which are detected to sense movement of an object in the vicinity of the electrodes. The electrodes are connected to a frequency selective circuit 54 such as an LC or RC resonant circuit which is in turn connected to a process circuit 56 which cooperates with the frequency selective circuit to form an oscillator. The oscillation frequency of the oscillator is compared in a comparator 56 with a reference frequency produced by a reference oscillator 55, the comparator having a counter, the count in which is representative of movement or proximity of the object.