JPH0577113B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a barcode detection device used in POS, logistics, production management, etc.

Prior Art FIG. 3A shows a specific circuit of a conventional floating binarization circuit.

Analog signal A is input to the inverting input of comparator 1. In addition, analog signal A charges and discharges capacitor 4 through diode 3, and threshold value B
(peak hold circuit). The threshold value B is input to the non-inverting input D of the comparator 1. Threshold B is passed through diode 3, so it is smaller than analog signal A by the dead zone of the diode (approximately
The signal change is delayed by 0.6V). Therefore, when the analog signal A changes from the peak by the dead zone, the analog signal A and the threshold value B intersect, and the output of the comparator 1 changes. The output of comparator 1 is pulled up to the power supply of the digital section for input to the CPU, RAM, etc. Therefore, the binary signal C changes depending on the digital power supply voltage level. When the binary signal C changes, hysteresis is applied to the non-inverting input D through the hysteresis resistor 5 to prevent the binary signal C from vibrating. FIG. 3B shows signal waveforms of the above circuit.

Such a binarization method is generally called a floating binarization method.

Problems to be Solved by the Invention However, strictly speaking, the binary signal C does not change at the point where the analog signal A and the threshold value B intersect, but when the analog signal A and the non-inverting input D intersect. The binarized signal C changes depending on the location. In addition, the non-inverting input D is the binary signal C
Since hysteresis is applied, the potential is slightly higher than the threshold value B of the binarized signal C.
Therefore, when the analog signal A is between the digital voltage and ground, the threshold value B and the non-inverting input D have the relationship as shown in Figure 4, and accurate binarization can be performed. For example, when the analog signal is at a higher potential than the digital voltage as shown in Figure 5, the relationship between the non-inverting input D and the threshold value B is as shown in Figure 5, the non-inverting input D is always at a lower potential than the threshold value B. Therefore, the high level of the binary signal C appears narrower and the low level appears thicker.

Further, since the potential of the threshold value B is connected to the binarized signal C through the hysteresis resistor, it approaches the potential of the binarized signal C when the diode is off. Figure 6 shows the waveform when looking at a barcode with poor space reflectivity, but the slope of analog signal A at the start margin is gentle, and the slope is such that threshold value B approaches binary signal C. Because the threshold value B and the binary signal C do not intersect, the start margin/first bar cannot be detected.

Also, as shown in Figure 7, when the diode is turned on from the off state, a rush current flows into the capacitor, causing the analog signal A to oscillate and the binary signal C.
affect.

Means for Solving the Problems In order to solve the above problems, the barcode detection device of the present invention includes a peak hold circuit that peak-holds an analog signal obtained by reading a barcode, and a peak hold circuit that peak-holds an analog signal obtained by reading a barcode. In a barcode detection device equipped with a floating binarization circuit that binarizes the analog signal using a comparator that compares the threshold value of the peak hold circuit with a threshold value of the peak hold circuit, the capacitor of the peak hold circuit is It is equipped with a means for discharging in synchronization with reading.

Function In the above configuration, by discharging the capacitor used in the floating binarization peak hold circuit in synchronization with barcode reading scanning,
The binarized signal can be lowered to low level, and the start margin and first bar can be recognized even in barcodes with spaces with poor reflectance.

Embodiment FIG. 1 shows an embodiment of the present invention.

Analog signal A is input to the inverting input of comparator 1. In addition, analog signal A is passed through inrush current prevention resistor 2 and diode 3 to capacitor 4.
is charged and discharged to generate threshold value B (peak hold circuit). The threshold value B is input to the non-inverting input D of the comparator 1. Since the threshold value B passes through the diode 3, the signal change is delayed from the analog signal A by the dead zone of the diode (approximately 0.6V). Therefore, when the analog signal A changes from the peak by the dead band, the analog signal A and the threshold value B
cross, and the output of comparator 1 changes.
Since the output of the comparator 1 is pulled up to the power supply of the comparator 1, the binary signal C changes depending on the power supply voltage level of the comparator 1. When the binary signal C changes, hysteresis is applied to the non-inverting input D through the hysteresis resistor 5 to prevent the binary signal C from vibrating.

Further, the discharging section 6 discharges the capacitor 4 in response to the synchronization signal E synchronized with the barcode reading scan, and the binary signal C is brought to a low level.

Incidentally, FIG. 2 shows signal waveforms of the main parts of the above circuit.

Effects of the Invention As described above, the present invention lowers the binary signal to a low level by discharging the capacitor used in the peak hold circuit for floating binary conversion in synchronization with barcode reading scanning. This allows the start margin and first bar to be recognized even in barcodes with spaces with poor reflectivity.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the main part of a barcode detection device showing an embodiment of the present invention, Fig. 2 is a signal waveform diagram of the main part, Fig. 3A is a conventional circuit diagram, and Fig. 3B is the same. Signal waveform diagrams of main parts, FIGS. 4 to 7 are various signal waveform diagrams in conventional circuits. 1... Comparator, 2... Inrush current protection resistor, 3... Diode, 4... Capacitor, 5...
...Hysteresis resistance, 6...Discharge section.

Claims (1)

[Claims] 1. Using a peak hold circuit that peak-holds an analog signal obtained by reading a barcode, and a comparator that compares the analog signal with a threshold value of the peak hold circuit, the analog signal is A barcode detection device comprising a floating binarization circuit for converting values into a value, the barcode detection device comprising means for discharging a capacitor of the peak hold circuit in synchronization with barcode reading.