Browse Prior Art Database

Optical Reading Wand

IP.com Disclosure Number: IPCOM000089775D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Laurer, GJ: AUTHOR

Abstract

Wands used for reading optically coded bar data are frequently adversely affected by ambient light. Generally, this light fluctuates in brightness at 120 Hz or, alternatively, is constant. In addition, the power of the light is distributed widely over the color spectrum from approximately 4000 angstroms to greater than 10,000 angstroms. Since this light is received by the photodetector in the wand along with the data signal, noise is introduced into the system.

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Optical Reading Wand

Wands used for reading optically coded bar data are frequently adversely affected by ambient light. Generally, this light fluctuates in brightness at 120 Hz or, alternatively, is constant. In addition, the power of the light is distributed widely over the color spectrum from approximately 4000 angstroms to greater than 10,000 angstroms. Since this light is received by the photodetector in the wand along with the data signal, noise is introduced into the system.

Classical solutions to this problem have not proved practical. The solution described herein alleviates the noise problem by subtracting the nondata signals contributed by the ambient light from the data plus nondata signals. A clear plastic sleeve surrounds the wand tip and is shielded from the sides. The sleeve looks at the same general area as does the tip. Ambient light is averaged and detected by a silicon detector after passing through an optical filter which passes all frequencies except that of the source illuminator, for example, 6328 or 6350 angstroms. A portion of the output of this detector is fed to one input of a differential amplifier while the data signal is fed to the other input. Thus, the nondata signal is nulled.

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