A control device provides a variable control signal to electrical apparatus and has a control member, such as a stylus or a turnable or slidable member, that is manipulated to vary the signal. Photoelectric sensors detect and track movement of the control member. The control member is disposed at the...http://www.google.com/patents/US20020060670?utm_source=gb-gplus-sharePatent US20020060670 - Circuit control devices utilizing electronic display screen light
