A control for use upon a solid panel, devoid of control shaft apertures, allows data entry by rotational positioning of a human member, such as one's finger, about a pattern of a plurality of interdigitated electrodes formed upon an interior surface of the panel. The position of the member varies the...http://www.google.de/patents/US4264903?utm_source=gb-gplus-sharePatent US4264903 - Capacitive touch control and display
