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Digital bar code slot reader with threshold comparison of the differentiated bar code signal

  • US 4,740,675 A
  • Filed: 04/10/1986
  • Issued: 04/26/1988
  • Est. Priority Date: 04/10/1986
  • Status: Expired due to Term
First Claim
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1. Apparatus for digitizing a reflectance signal obtained from scanning a bar code, comprising:

  • a differentiator responsive to the reflectance signal from the bar code to produce a first signal proportional to the slope of the reflectance signal;

    a peak detector responsive to the first signal to produce a second signal proportional to the peak amplitude of the first signal;

    means for inverting the second signal to produce a third signal;

    a positive threshold comparator responsive to the first signal and to the second signal to produce a first digital output signal when the amplitude of the first signal goes above the amplitude of the second signal;

    a negative threshold comparator responsive to the first signal and to the third signal to produce a second digital output signal when the amplitude of the first signal goes below the amplitude of the third signal; and

    means for combining the first and second digital output signals to produce a third digital output signal corresponding to the input reflectance signal.

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