Bar code reader with comparison of bar widths and signal transitions

Abstract

In a bar code reading device in which an image of a bar code is Converted into an information signal having transitions corresponding to bar data in the bar code, a first counter counts the numbers of pulses of a clock signal provided by a reference clock corresponding to the periods between transitions of the information signal. The pulse counts are stored in a first memory. A second counter counts the number of transitions in the information signal and stores the number of transitions in a second memory. Since the procedure carried out by the second counter can occur in a very short time, the number of bar data can correctly be counted even if the bar code has defective bar data formed by misprinting. Accordingly, an ALU is able to decide whether or not the bar code is recognized correctly through a comparison of the number of periods between transitions stored in the first memory and the number of transitions stored in the second memory. Thus, incorrect bar code reading operations can be prevented.