| 摘要 |
A false bar code inhibitor circuit includes a detector, a signal restore circuit, a comparator, a software controller, and a high impedance clamp circuit. Basically, the detector circuit detects the first transition from either high to low reflectivity or low to high reflectivity. The transition triggers the signal restore circuit which is set for a time constant which is longer than the longest possible time needed to encounter another transition during a valid bar code read. Each time a transition is encountered, the signal restore circuit is triggered. The externally adjustable comparator circuit compares the output from the signal restore circuit against a limit, which can be adjusted by the software controller. The output of the comparator drives a clamp which controls when the bar code digitizer can pass an output. With the software controller, the output of the comparator can be controlled allowing for control over the digitizer output. With the false bar code inhibitor a false bar generated at the start of a bar code scan can be masked. The inhibitor circuit also creates a "window" which is used to mask out valid bar code from a signal. Additionally, the inhibitor circuit allows for external control for adjusting threshold levels and for external control over the bar code digitizer output.
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