Remote control unit
A remote control system adapted to selectively advance one or more selector switches including a source of optical signal disposed in proximity with a first photo cell, a portable return reflector or retroreflector and means for selectively masking the reflector. The signal developed across the first photo cell is referenced against a second photo cell, such second photo cell being located away from the associated source such that only background signals impinge thereon. In a further embodiment, a plurality of first photo cells are combined with the second photo cell, each such first photo cell being selectively filtered to sense discrete signal frequencies or polarities and a plurality of return reflectors or retroreflectors, selectively filtered in correspondence to the photo cell filters, are disposed for selective exposure by associated masking means.