JPH0253190A - Bar code detector - Google Patents

Abstract

PURPOSE:To allow an analog signal to be always between the high level and low level of a binarization signal and to execute exact binarization by obtaining a signal to load hysteresis to the peak holding circuit output of a floating binarization circuit from the power source voltage of a comparator. CONSTITUTION:An analog signal A executes the charge/discharge of a capacitor 4 and generates a comparing reference value B. The comparing reference value B is inputted to a non-inverting input D of a comparator 1. Since the comparing reference value B is passed through a diode 2, the change of a signal is delayed to the analog signal A only by the dead zone part of the diode. Thus, when the analog signal A is changed from a peak by the dead zone part, the analog signal A and the comparing reference value B are across and the output of the comparator 1 is switched. Since the output of the comparator 1 is pulled up by the power source of the comparator 1, a binarization signal C is switched at the power source voltage level of the comparator 1. When the binarization signal C is switched, the hysteresis is loaded through a resistor 5 for hysteresis to the non-inverting input D and the binarization signal C is prevented from being oscillated.

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, and the like.

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

The analog signal M is input to the inverting input of comparator 1. Further, the analog signal M charges and discharges a capacitor 3 through a diode 2, and generates a comparison reference value B (peak hold circuit). The comparison reference value B is input to the non-inverting input of the comparator 1. Comparison reference value B is diode 2
Because it passes through the analog signal, the change in the signal is delayed by the dead zone of the diode (approximately 0.6 V). Therefore, when the analog signal M changes from the peak to the dead zone, the analog signal M intersects with the comparison reference value B, and the output of the comparator 1 changes. The output of comparator 1 is CPU
- Pulled up to the power supply of the digital section for input to 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 through the hysteresis resistor 4.
prevents it from vibrating. FIG. 3(b) 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, analog signal signals and threshold values B
The binary signal C does not change at the point where the analog signal M and the non-inverting input intersect, but the binary signal C changes at the point where the analog signal M and the non-inverting input intersect. Further, since the non-inverting input is hysteretized by the binarized signal C, it takes a potential slightly higher than the comparison reference value B than the binarized signal C.

Therefore, when the analog signal M is between the digital voltage and the ground, the threshold value B and the non-inverting input have a relationship as shown in Figure 4, and accurate binarization can be performed. For example, as shown in Figure 6, when the analog signal is at a higher potential than the digital voltage, the relationship between the non-inverting input and the comparison reference value B is as shown in Figure 6. Since the signal C is at a low potential, the high level of the binary signal C appears narrower and the low level appears thicker.

Further, since the potential of the comparison reference value B is connected to the binary signal C through the hysteresis resistor, it approaches the potential of the binary signal C when the diode is off. Figure 6 shows the waveform when looking at a barcode with poor space reflectance, but the slope of the analog signal at the star margin is gentle, and the comparison reference value B is the binary signal C.
Since the slope approaching , is steeper, the comparison reference value B and the binarized signal C no longer intersect, and the start margin/first bar cannot be detected.

Further, when the diode is turned on from an off state as shown in FIG. 7, an inrush power flows into the capacitor, causing the analog signal C to oscillate and affecting the binary signal C.

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 barcode reading scanning;
In a barcode detection device equipped with a floating binarization circuit that binarizes the analog signal using a comparator that compares the previous analog signal with a comparison reference value of the previous peak hold circuit, the output of the first half comparator is It is equipped with a pull-up circuit to the power supply of the comparator.

Further, another barcode detection device of the present invention is characterized in that the peak
The apparatus is equipped with means for discharging the capacitor of the hold circuit in synchronization with barcode reading and scanning.

Furthermore, another bar code detection device of the present invention is constructed by connecting a resistor in series to the circuit for charging and discharging the capacitor of the peak hold circuit.

Effect In the above configuration, the first peak of the floating binarization circuit is
By taking a signal that applies hysteresis to the hold circuit output (comparison reference value) from the power supply voltage of the first comparator, the analog signal can always be accurately binarized between the high level and the low level of the binarized signal.

In addition, by discharging the capacitor used in the peak hold circuit for floating binarization in synchronization with barcode reading scanning, the binarized signal can be lowered to a low level, and the reflected Even in barcodes with poor spacing, the start margin and first bar can be recognized.

Furthermore, by inserting an inrush current prevention resistor in series with the circuit that charges and discharges the capacitor used in the peak hold circuit of the floating binarization, inrush current flowing into the capacitor can be prevented, resulting in oscillation of the analog signal. can be prevented.

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

The analog signal M is input to the inverting input of comparator 1. Further, the analog signal M charges and discharges a capacitor 4 through an inrush current prevention resistor 2 and a diode 3 to generate a comparison reference value B (peak hold circuit). The comparison reference value B is input to the non-inverting input of the comparator 1. Since the comparison reference value B passes through the diode 2, the change in the signal is delayed from the analog signal M by the dead zone of the diode (approximately o, eV). Therefore, when the analog signal M changes from the peak to the dead zone, the analog signal M and the reference value B are compared.
intersect, and the output of comparator 1 changes. Since the output of comparator 1 is pulled up to the power supply of comparator 1, the binary signal C changes depending on the power supply voltage level of comparator 1.

Thereafter, input to the CPU and RAM is performed through a level converter. When the binary signal C changes, hysteresis is applied to the non-inverting input through the hysteresis resistor 6 to prevent the binary signal C from vibrating.

Further, the discharge section 6 discharges the capacitor 4 according to the synchronization signal K that is synchronized with the barcode reading scan, and the binary signal C becomes 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 provides that the analog signal is always It is between the high level and low level of the binarized signal, allowing accurate binarization.

In addition, by discharging the capacitor used in the early peak hold circuit of floating binarization in mI in synchronization with barcode reading scanning, the binarized signal can be lowered to a low level, and the reflected Even in barcodes with poor spacing, the start margin and first bar can be recognized.

Furthermore, by inserting a rush current prevention resistor in series with the circuit that charges and discharges the capacitor used in the peak hold circuit of the floating binarization, oscillation of the analog signal can be prevented, which can prevent rush current flowing into the capacitor. can do.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a 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, and Fig. 3 ((
A) is a conventional circuit diagram, Fig. 3 (rumored is a signal waveform diagram of the same main part, and Figs. 4 to 7 are various signal waveform diagrams in the conventional circuit. 1...Comparator, 2...Inrush current protection resistor, 3...Diode, 4...
・Capacitor, 6...Hysteresis resistor, 8.
...discharge section. Name of agent: Patent attorney Shigetaka Awano and 1 other person
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Claims (3)

[Claims] (1) Using a peak hold circuit that peak-holds the analog signal obtained by barcode reading and scanning, and a comparator that compares the previous analog signal with a comparison reference value of the previous peak hold circuit, the analog signal is A barcode detection device equipped with a floating binarization circuit for binarizing, which includes a circuit that pulls up the output of a first comparator to a power source of the first comparator. (2) Using a peak hold circuit that peak-holds the analog signal obtained by barcode reading and scanning, and a comparator that compares the previous analog signal with the comparison reference value of the previous peak hold circuit, the analog signal is A barcode detection device comprising a floating binarization circuit for binarizing, the barcode detection device comprising means for discharging a capacitor of the peak hold circuit in synchronization with barcode reading scanning. (3) Using a peak hold circuit that peak-holds the analog signal obtained by barcode reading scanning and a comparator that compares the previous analog signal with a comparison reference value of the previous peak hold circuit, the analog signal is A barcode detection device comprising a floating binarization circuit for converting into values, wherein a resistor is connected in series to a circuit for charging and discharging a capacitor of the peak hold circuit.