Bar code scanning system for automatically maintaining constant the

Abstract

A system for bar code reading and scanning is provided having automatic bar code signal size control. In the first embodiment of the system, a processor selects on successive scans of a bar code one of a plurality of different optical power levels from a laser diode which provides a light beam illuminating the bar code. This selection is responsive to the size of the signal from a photo-detector which receives returned light from the bar code during scanning. The signal size is detected by a signal size detecting circuit, and is measured by the processor during scanning. In a second embodiment of the system, the processor calculates an optical power level after every two consecutive scans across the bar code. The laser power level is calculated differently for alternative scans occurring in different orders (even or odd counting from the first scan). For even scans, the power is calculated based upon signal size and power level on one of the prior two scans of the bar code, while for odd numbered scans (except the first scan), the power level is in a proportionately opposite relationship to the power level on the prior scan about an average power level. In a third embodiment of the system, the processor calculates the power for the next scan after each scan across the symbol. This calculation is responsive to the power level and the detected signal size of the preceding scan. In both the second and third embodiments, the laser is set to a starting power level on the first scan of the bar code.