Identification system

Abstract

A reader identifies information, such as the identity of an object at a transponder, provided in binary form by the transponder. The reader initially generates a pulse which activates the transponder into transmitting a series of signals, such as by magnetic induction, to the reader. Upon each count of a particular number of signals in the reader, the reader generates an additional pulse which causes the transponder to transmit a new series of signals to the reader. The generation of the pulses by the reader may occur through the charge and discharge of energy in a storage member such as a capacitance. The series of signals produced by the transponder may have either a first frequency or a second frequency. The signals may be generated in each sequence at the first and second frequencies in an order dependent upon (a) the binary code identifying the object at the transponder and (b) the polarity of the pulse produced by the transponder in such sequence. The reader then identifies the information by demodulating the signals received by it at the first and second frequencies. The reader is able to interrupt at any time the generation of the sequence of signals at the transponder when it does not receive the signals transmitted by the transponder. The reader then operates on a free running basis to generate pulses of opposite polarity at a relatively low frequency.