Abstract: An optical scanner in a retail store checkout stand includes a single item detector upstream of the scanner window. Output signals from the item detector and from symbol recognition logic are used to open and close a shutter in the beam path of the scanner laser. The shutter is opened and a first time out sequence is started when the beam path is interrupted. A second, short time out sequence is restarted each time a valid symbol is recognized. A third time out sequence of intermediate length supersedes the first time out sequence when the beam path is cleared. The laser shutter is closed and the symbol is transferred to a terminal or controller upon the completion of any active time out sequence or upon recognition of a predetermined number of identical symbols, whichever comes first.

Abstract: A scanning system includes a pair of buffer memories for alternately accumulating strings of signals which may contain bar coded label data. Candidate selection logic circuits examine incoming signals to generate a candidate signal when a string of signals satisfies gross logical tests. A control counter responds to the incoming signals and to the candidate signal to select an alternate buffer memory only when the active memory is fully loaded and contains at least part of a label candidate. The contents of the fully loaded memory are transferred to a processor for further analysis while incoming signals are routed to the alternate memory.