A device for transmitting the condition of a switch comprising a first assembly consisting of a switch, a first pair of coils serially connected when the switch is closed, and a second assembly consisting of a second pair of coils, magnetically coupled to each other. A first coil of the second pair generates...http://www.google.ca/patents/US4057783?utm_source=gb-gplus-sharePatent US4057783 - Device for transmitting the condition of a switch between two parts in relative rotary movement
