| 摘要 |
PURPOSE:To read the bar code accurately independently of its type and precision, by changing the threshold of a adetecting circuit in accordance with the magnitude of the bar code read signal. CONSTITUTION:A light projected from a light emitter PD is reflected by a bar code string BC and is converted photoelectrically in a photodetector PT to obtain a sense signal. This signal is amplified in an amplifier AMP and is inputted to a comparator CMP. Threshold data SLDa-SLDh outputted from a programmable controller CPU are sent to a D/A converter DAC, and a threshold signal SL is sent from the converter DAC to the comparator CMP. Thus, sense data SD in the threshold SL is given to the CPU. Consequently, the CPU changes these thresholds to receive sense data SD and performs the read control based on level change |
