David Allen Swift

US Patent:

40669106, Jan 3, 1978

Filed:

Apr 9, 1976

Appl. No.:

5/675467

Inventors:

David Merton Swift - Palo Alto CA

Assignee:

Lawrence Systems, Inc. - San Francisco CA

International Classification:

G06K 710

US Classification:

250555

Abstract:

A photoelectric data card system is disclosed in which the cards are transmissivity-coded, so that light of a particular wave length and intensity is transmitted in varying degrees of different code digit representing areas of the cards, and thus the intensity of the light emerging from each of these code digit representing areas can be photoelectrically interpreted as the value of the digit represented by that area. A laminated card for use in this system is disclosed in which the transmissivity levels of the digit representing areas are provided by halftone printing on an inner lamination of dark-pigmented plastic card stock, and the inner lamination is sealed between two white-pigmented laminations of plastic card stock, the white-pigmented laminations being pigmented to such an extent that neither the location of the digit representing areas nor the values of the digits represented can be determined by casual inspection of the card. The card reader of the disclosed system includes a light source-photosensor digit reading pair for each digit representing area to be read and an additional light source-photosensor reference pair for determining the transmissivity of a reference area of the card. In order to eliminate the reading errors arising from batch-to-batch variations in the transmissivity of available card stock materials, the reference voltage levels with which the output signals of the digit reading circuits are compared for classification as to digit value are all proportionately varied in accordance with the magnitude of the output signal from the reference pair.