KR900000857Y1 - Light detecting circuit of bar code scanner - Google Patents

Abstract

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Description

Optical detection circuit of barcode scanner

1 is a block diagram of the present invention.

2 is a concrete circuit diagram of FIG.

3 is an illustration of a barcode lead

4 is an operational waveform diagram of each part of FIG.

* Explanation of symbols for main parts of the drawings

10: light detector 20: amplifier

30: status signal generator 40: pulse generator

The present invention relates to a pen type bar code scanner (Pen type bar code scanncr) circuit, in particular to respond to variations in the input signal according to the shape of the bar code, the light of the barcode scanner that can generate a digital pulse signal according to the width of the bar code black and white It relates to a detection circuit.

In general, a bar code refers to displaying product information such as a price of a product, a manufacturer, etc. on a product in black bars and white bars.

Therefore, in the barcode scanner, the state must be converted into a logic signal without changing the line width ratio of the monochrome pattern.

In this case, a circuit is needed to change the logic between the black and white bars. Such a circuit is called a barcode photodetector circuit.

In this case, the photodetector circuit changes the photodetector signal into a digital signal compared with the threshold signal. However, there is a possibility that the photodetector uses a fixed threshold signal to cause a deformation of the output signal.

In other words, when the fixed threshold signal is used, there is a problem in that the barcode is different from the barcode information due to the difference in density between black and white bars during the printing of the barcode, and the barcode information due to the external environment during scanning.

Accordingly, an object of the present invention is to provide a circuit capable of accurately determining the signals of the black bar and the customer bar by detecting a threshold voltage corresponding to the positive peak and the negative peak of the light detection signal.

It is still another object of the present invention to provide a circuit that can check a signal state of a white bar and a black bar and process an error signal when a difference below a predetermined voltage occurs to prevent the generation of false information.

1 is a block diagram according to the present invention. A light detector 10 for scanning light with a bar code and converting a signal detected according to black and white bars into an electrical signal; An amplifier 20 for amplifying the output of the photo detector 10; Generate a positive peak and negative peak signal according to the output of the amplifier 20. And a state signal generator 30 generating a threshold signal corresponding to the middle of the two peak signals, and simultaneously generating a control signal in which the positive peak signal is voltage-dropped to a predetermined magnitude. Comparing the output of the amplifier and the threshold signal to generate a digital signal according to the black and white logic circuit of the barcode. And a pulse generator 40 for comparing the error control signal and the negative peak signal to cut off the output of the digital conversion signal at a predetermined voltage difference or less.

Based on the above-described configuration will be described the present invention in detail.

When the barcode is read, the amount of reflected light of the black bar and the white bar is greater in the white bar, and the light detector 10 converts the change according to the amount of reflected light of the black bar and the white bar into an electrical signal.

Then, the amplifier 20 amplifies the detected weak signal.

At this time, the output waveform of the amplifier 20 changes the reflected light amount due to a difference in black and white concentration that may occur during the printing of the barcode or an external influence when the barcode is read in the photodetector 10 so that the negative peak and the positive peak voltage change. Or a change in the DC voltage level of the signal.

At this time, the state signal generator 30 detects the negative peak voltage and the positive peak voltage according to the change of the input level, and generates a threshold signal as an intermediate value between the two signals.

The positive peak voltage is dropped to a predetermined magnitude to generate an error control signal.

Then, the field generating unit 40 compares the output of the amplifying unit 20 with the threshold hold signal to determine the output signal as "high" and "low".

In addition, when the voltage difference between the positive peak voltage and the negative voltage becomes less than or equal to the predetermined voltage by comparing the negative peak and the error control signal, an error is likely to occur, so the output is prohibited.

2 is a concrete circuit diagram of FIG. Resistance (R1). An optical detector 10 composed of a light emitting diode LD1 and a photodiode PDl, an amplifier 20 composed of a resistor R2, a capacitor C1 and an operational amplifier OP1, and a comparator OP2-OP3 ) And a state signal generator 30 comprising a diode (D1-D4), a capacitor (C2-C3) and a resistor (R3-R4). Comparator (OP4-OP5). Resistance (R5-R6). It consists of the pulse generator 40 comprised from the Zener diodes ZD1-ZD2 and the latch F1.

3 is a diagram illustrating detecting a barcode through the light emitting diode LD1 and the photodiode PDl.

4 is an operation waveform diagram of each part of FIG. 2, where (W) is a form diagram of a barcode printed on a product, (X) is an output of the photodiode PD2, and (Y) is a photodiode of the photodiode PD2. (Y) is the output of the operational amplifier OP1, PPS is the positive peak signal of the operational amplifier OP2, NPS is the negative peak signal of the operational amplifier OP3, and THS is the positive peak and negative peak signal. This is the threshold signal, which is the intermediate value of, and is the output of the (Z) null latch F1.

The detailed circuit diagram according to the present invention by the above configuration will be described in detail with reference to FIGS. 3 and 4.

When the power supply VCC is applied to the light emitting diode LDl through the resistor Rl, the light emitting diode LDl emits light and is received by the photodiode PDl according to the amount of light reflected from the barcode.

At this time, since the bias voltage is not applied to the photodiode PDl, it is possible to maintain a proportional relationship between the light reception amount and the output until the minute light amount is not affected by the dark current.

However, when the photodiode PDl reads the barcode as shown in FIG. 3, when the peripheral illumination suddenly changes or a change in the external environment occurs, the amount of received light may change or the DC voltage level of the signal may change.

That is, when the external environment is changed during the barcode read as shown in FIG. 4 (W), the light reception amount of the photodiode PDl is changed, and the output of the operational amplifier OP1 changes the DC level of the signal as shown in FIG. 4 (X). Can be.

As described above, when the barcode is continuously detected by the light emitting diode ⒧ D1 and the photodiode PDl as shown in FIG. 4 (X), the operational amplifier OP1 inverts the signal as shown in FIG. 4 (Y). Let it be.

In this case, when the modified photodetection signal is compared with the fixed threshold signal as shown in FIG. 4, a digitally converted signal is generated in a form different from the original barcode.

Therefore, the present invention detects the positive peak signal (hereinafter referred to as PPS) and the negative peak signal (hereinafter referred to as NPS) of the signal outputting the operational amplifier OP1 and then the positive peak signal PPS. The intermediate value of the negative peak signal NPS is used as a threshold signal (hereinafter referred to as THS).

First, looking at the detection peak of the positive peak signal PPS, the signal of the "high" level outputting the operational amplifier OP1 is charged to the capacitor C2 through the comparator OP2 and the diode D1.

At this time, when the output of the operational amplifier OP1 is smaller than the charging voltage of the capacitor C2, a "low" signal is output from the comparator OP2, so that the capacitor C2 maintains a positive peak voltage as shown in FIG. do.

In addition, looking at the detection process of the negative peak signal NPS, the signal of the "low" level outputting the operational amplifier OP1 is applied to the non-inverting terminal of the comparator OP3, where the comparator OP3 outputs the "low" signal. Thus, the voltage charged in the capacitor C3 starts to be discharged through the diode D2.

At this time, when the output of the operational amplifier OP1 is greater than the charging voltage of the capacitor C3, the discharge of the capacitor C3 is terminated by the comparator OP3 and the diode D2 to maintain the negative peak voltage as in the NPS of FIG. Done.

Therefore, a threshold signal THS, which is a voltage of 1/2 of the positive peak signal PPS and the negative peak signal NPS, is generated between the resistors R3-R4, which is shown in FIG. Likewise, the signal corresponds to the output of the photodiode PD1 changed by the external environment.

At this time, the comparator (○ P4) compares the output of the operational slave amplifier OP1 and the threshold hold signal THS as shown in FIG. 4 (Y) to generate a logic signal according to the black and white of the barcode, the threshold hold signal THS Since is adjusted according to external influences, it is possible to extract the exact boundary of black and white.

In addition, the positive peak signal PPS is dropped by about 1.4V through the diode D3.D4 and applied to the non-inverting terminal of the comparator OP5.

Then, the comparator OP5 outputs a "low" signal when the negative peak signal NPS input to the inverting terminal is larger than the positive peak signal PPS dropped by about 1.4V.

This is to make the currently detected signal valid only when the positive peak signal PPS and the negative peak signal NPS differ by 1.4 V or more.

Therefore, the 1.4V dropped positive peak signal is a signal for detecting an error occurrence.

The output of the comparator OP4 is converted to a TTL level through the zener diode ZDl, and then converted to a bar code decoder through a latch F1, and then a bar code decoder Bar through a latch F1. Code Decoder).

At this time, the latch Fl is enabled when the comparator OP5 outputs the "high" signal (if the difference between the PPS and the NPS is 1.4 V or more) to supply the output of the comparator (○ P4) to the barcode decoder, In case of signal (when PPS and NPS are below 1.4V), error is large and is disabled.

As described above, in the process of generating the pulse output according to the width of the barcode from the light detection of the bar code scanner, the black and white concentration difference of the barcode that may be caused by the poor printing or storage condition and the external environment are caused. As a result, even if the level of the barcode detection signal changes, it can be converted into a digital signal accurately, and it is possible to detect whether or not an error occurs due to the difference between the black and white levels, and thus to cleanly detect the product information recorded by the barcode. have.

Claims (1)

Light of a barcode scanner having a light detector 10 for scanning light with a barcode and converting a signal detected according to black and white bars into an electrical signal, and an amplifier 20 for amplifying the output of the light detector 10. In the detection circuit, a positive peak PPS and a negative peak signal NPS according to the output of the amplifier 20 are generated, and a threshold signal THS corresponding to the middle of the two peak signals is generated. At the same time, a bar code is obtained by comparing the output of the amplifier signal with the state signal generator 30 generating the error control signal in which the positive peak signal is lowered to a predetermined magnitude, the output of the amplifier 20 and the threshold hold signal THS. And a pulse generator 40 for generating a digital signal according to the black-and-white logic conversion and blocking the output of the digital conversion signal when the error control signal and the negative peak signal (NPS) are compared to be less than a predetermined voltage difference. to Light detection circuit of the bar code scanner.