GB1445846A - Bar code scanner apparatus - Google Patents

Abstract

1445846 Bar code reading system NORAND CORP 17 July 1973 34067/73 Heading G4M [Also in Division H3] A reading system for a bar code in which bars have two possible widths each of two possible characteristics decodes bars of one of the widths and either polarity as one binary digit and the other width and either polarity as the other bit. In an optical embodiment signals from a light detector are amplified and passed through a circuit providing amplitude and level control and feeding a cross-over detector which clips the level controlled signal to remove negative levels, to square the signals and produce true and inverse pulses (Fig. 3, not shown). The true and inverted pulses feed flip-flops which via a switching delay produce pulses occurring for each cross-over point of the signal (Fig. 7a, not shown). The amplified signal from the detector is applied 67 to a peak detector (Fig. 4) where diode 69 supplies a negative rectified wave and diode 70 supplies a D.C. level 72 via capacitor 73 charged to the negative peak of the waveform. In attenuated D.C. level 72a is fed to operational amplifier 80 which also receives the signal 71 from diode 69 to produce a series of pulses corresponding 81 to the periods when the peak of the waveform from diode 69 exceeds the attenuated level from diode 70 and corresponds to the detection of wide white bars. Diode 92 rectifies the signal on line 67 to pass black bar information and pulses from a flip-flop representing squared data pulses (Q62, Fig. 7a, not shown) are fed on line 68 to charge capacitor 97 which will be charged by wide bars to a value twice that achieved for narrow bars, 99, Fig. 7b. The two signals are summed and compared with a reference 108 which is situated between the peaks of the wide and narrow bar signals regardless of variations in reflectivity of the black bars to produce pulses corresponding to the wide black bars. The white and black bar signals are fed to OR gate 86. The data signals and the cross-over pulses are fed via shift registers (Fig. 5, not shown) to a display unit and to START and STOP code detectors. A counter (Fig. 6, not shown) counts the number of bits in each digit and the number of bits in six digits which is the amount displayed. An audio alarm is produced if an error in the number of bits occurs or if a STOP code is not received. The gates in the logic circuitry are enabled when the probe is placed against the document. It is stated that a detector for magnetic markings may be used.