Abstract: A recognition and identification key comprising a substrate formed from an electrically insulating material, a first sheet of conductive material formed on a first surface of the substrate in a looping pattern so as to provide an inductive element, and a capacitive element coupled to the first sheet such that the elements are resonant at a first frequency, at least one of the inductive and capacitive elements capable of being changed such that the key is resonant at a second frequency, and a method of adapting the resonant frequency.

Abstract: An electronic recognition and identification system for recognizing and identifying any one of a family of electrically-coded external objects. The system comprises internal electronics including a pulse widening circuit which enables the system to be responsive to each of the codes of the family of external objects.

Abstract: An electronic recognition and identification system for identifying one of a plurality of electrically coded keys, each having at least one tuned electrical circuit which is resonant at at least one of a plurality of predetermined frequencies. The system comprises a sweep oscillator for generating an alternating current signal. The alternating current signal has a frequency which varies with time over a range of frequencies including the plurality of predetermined frequencies. A condition pulse generating network is connected to the oscillator and produces a condition pulse when one of the keys is proximate thereto and when the frequency of the alternating current signal passes through its predetermined frequency. A plurality of reference pulse generating circuits are selectively connected to the oscillator by a sequential multiplexer.