A system (10) for detecting the state of a switch device (60) includes a driver circuit (40) having an output (42) operative to provide a driver output signal. An indicator (44) is electrically connected between the driver circuit (40) and the switch device (60). The indicator (44) is activated in response...http://www.google.es/patents/US6140622?utm_source=gb-gplus-sharePatente US6140622 - System for detecting the state of a switch device
