An active type range finder has a light-emitting element which is pulsatively driven to project light pulses on an object to be photographed. A photodetector element receives the light reflected from the object and produces a photoelectric output signal proportional to the amount of received light. A...http://www.google.co.uk/patents/US4497560?utm_source=gb-gplus-sharePatent US4497560 - Control circuit for active type range finder
