| 摘要 |
<p>A bar code reader (10) comprises two photodetectors (44, 48) disposed a fixed distance apart. Independent circuitry (56, 58; 66, 68) is connected to each photodetector to provide first and second digital signals when the photodetectors detect an edge in a bar code. As the reader (10) is scanned across the code the signals are timed and are compared in a central processing unit (76) to calculate the scanning velocity, from which the absolute spacing of the bars is determined.</p> |
