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Identification card with concealed coding and a simple reader module to decode it

  • US 4,538,059 A
  • Filed: 09/13/1982
  • Issued: 08/27/1985
  • Est. Priority Date: 09/16/1981
  • Status: Expired due to Term
First Claim
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1. The combination of an identification card and reading apparatus for said card, said combination comprising:

  • (a) a card provided with a concealed code which, while being invisible to the naked eye when viewed in visible light, is readable in transmission using infra-red radiation, said code being characterized by successive digits represented by transparent windows alternating with regions opaque to infra-red radiation, the said windows and opaque regions being arranged along a line parallel to one edge of the card and each window representing a binary digit of the code with one binary digit being represented by wide rectangular windows while the other binary digit is represented by significantly narrower windows;

    (b) an optoelectric reader consisting of a single source of infra-red radiation and a single infra-red detector arranged to either side of a card slot to enable the coded card to be read on passage along the slot; and

    (c) an electronic system responsive to a signal from said reader and having a first threshold detector arranged to produce a clock signal each time that the reader detects a window in the card and a second threshold detector arranged to produce a second signal to represent a binary one when a second threshold level of output from the electronic reader is passed, the absence of said second signal when a clock signal is detected indicating the presence of a binary ZERO whereby said code windows are self-clocking and the code can be scanned independently of the rate at which said card is moved along the slot.

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