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Decoding Logic for a Three Slit Delta Distance Bar Code Scanner

IP.com Disclosure Number: IPCOM000081496D
Original Publication Date: 1974-Jun-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Crouse, WG: AUTHOR [+2]

Abstract

Described is a simple logic circuit for decoding a delta distance bar code, which is scanned by a three-aperture scanner. The bar code has alternating areas or bars of different reflectivity. The bars have two widths. Individual characters or groups of characters are provided with an initial known reference bar. The first bit of a binary code is encoded in the second bar. If the bit to be encoded is a "1", the second bar is made equal to the reference bar. If the second bit is a "0", the second bar is made different (either smaller or larger depending on the size selected for the reference) than the first bar. This bar is now used as a reference for the next or second bit to be encoded. The process continues until all bits are encoded.

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Decoding Logic for a Three Slit Delta Distance Bar Code Scanner

Described is a simple logic circuit for decoding a delta distance bar code, which is scanned by a three-aperture scanner. The bar code has alternating areas or bars of different reflectivity. The bars have two widths. Individual characters or groups of characters are provided with an initial known reference bar. The first bit of a binary code is encoded in the second bar. If the bit to be encoded is a "1", the second bar is made equal to the reference bar. If the second bit is a "0", the second bar is made different (either smaller or larger depending on the size selected for the reference) than the first bar. This bar is now used as a reference for the next or second bit to be encoded. The process continues until all bits are encoded.

A typical scanner for a minimal 8/16 mil bar width is illustrated in Fig. 1 and includes a "C" slit, a "B" slit spaced approximately 2O mils from the "C" slit and an "A" slit spaced 8 mils from the "B" slit. The figure also includes a typical bar code adjacent the scanner and scan is illustrated by an arrow.

Decoding consists of counting the positive and negative transitions seen by slits A and B, and sampling the counters at both the positive and negative transitions seen by slit C. One embodiment is illustrated in Fig. 2, in which one binary flip-flop counter 10 is used to count the positive transitions of slits A and B, and another binary flip-flop counter 11 is used to count the negative transitions of these slits. AND gates 12 and 13 under control of the positive and negative C slit transitions, respectively, are used to sample the flip-flops. The outp...