Finger operable control device

A finger operable control device comprising a sensor having a central electrically conductive plate, a first pair of electrically conductive plates on a first axis and spaced from opposite edges of the central plate to form a first pair of capacitors therewith having substantially equal capacitance, a second pair of electrically conductive plates on a second axis different from the first axis and spaced from opposite edges of the central plate to form a second pair of capacitors therewith having substantially equal capacitance, characterised in that opposite members of each pair of plates are driven by antiphase outputs of a quadrature-phase generator and the central plate is connected to a detector capable of sensing the magnitude and/or phase of the signal therefrom caused by capacitive imbalance induced by presence of either a finger or a finger-operable earthed object placed on or near the conductive plates when the finger or object is displaced laterally from the intersection of the two axes.