Dual edge detector for bar codes
Signal processor method and apparatus
Method and apparatus for reading label bar codes
Dual threshold comparator circuit
Wave shaping circuit for electro-optical code readers Patent #: 4335301
ApplicationNo. 06/850311 filed on 04/10/1986
US Classes:235/462.27, Analog to square wave converter (e.g., digitizer, binarizer, slicer)235/436, Readout control250/568Digital information
ExaminersPrimary: Cardillo, Raymond F. Jr.
Assistant: Weinhardt, Robert A.
Attorney, Agent or Firm
International ClassG06K 7/10 (20060101)
AbstractA digital bar code slot reader provides low first bar error rates and a wide scan speed range for bar codes on laminated badges and tags, and is also capable of reading bar codes on paper. The reflectance waveform from the bar code is differentiated in order to find the regions of high slope. The differentiated signal is peak detected to find the amplitude of the slope occurring at the initial card edge. This peak detected value is used to generate thresholds to be compared to the differentiated reflectance signal during the rest of the scan. When the slope of the reflectance signal is above the positive threshold or below the negative threshold, a switching signal is produced. To compensate for the lower amplitude output of the differentiator at low scan speeds, one of the amplifiers in the circuit produces a higher gain at low frequencies than at high frequencies.