Solid state optical reader with bi-directional protocol

摘要

An apparatus for reading an optical bar code on a transparent film uses a linear array of light sources and a linear, solid-state sensor located parallel with array. LED's are energized selectively in groups to avoid overlapping shadows on the sensor. A novel algorithm is used to reconstruct the shadowgraphs or image segments by searching for a transition (mark/space edge in the bar code) in an overlap zone at the boundary of adjacent segments on the sensor. Conventional techniques are then used to decode the reconstructed electronic image of the bar code. The apparatus is particularly useful in an electronic presentation system wherein the numeric value of the bar code is an image reference number (IRN) which is used to access a host computer and display a graphic image associated with the IRN. A novel bi-directional protocol is also presented for providing communications between the optical reader and the host computer. The protocol directs the host computer to download all IRN's for a given presentation to the reader. The reader can then locally determine if a bar code on a card corresponds to a valid IRN in the current presentation. The protocol may be adapted to download certain display control information and send associated control signals to the host computer based on keyboard input at the reader.