JP2001043306A - Light quantity control method of led for bar code irradiation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the quantity of light and also control luminance within a fixed range without using a variable resistor for controlling the luminance of an LED for light source for irradiating a bar code by varying a pulse width according to a control program. SOLUTION: A CPU 3 incorporates a variable pulse width control function (PWM) and the pulse of an LED2 (12) for irradiating the bar code is driven by a PWM port 11 through a resistor R4. The CPU 3 executes a previously registered luminance control program and generates the pulse of the duty ratio of an initial setting value from the PWM port 11 and the LED2 (12) is turned on. The quantity of light emitted from a bar code reader is then measured by an illumination meter. When the quantity of light exceeds a proper value, the duty ratio is gradually reduced by pressing a prescribed key predetermined by a program. When the quantity of light is less than the proper value, it is controlled so as to be settled within the proper value by gradually increasing the duty ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pen-type handy terminal, which has a built-in bar code reader and uses a LED as a light source to control the lighting method.
This is to reduce the variation in the luminance of the ED.

[0002]

2. Description of the Related Art Conventionally, a pen-type handy terminal 60 with a built-in bar code reader is of the type shown in FIG. In this case, a visible light LED is used as an LED to be used so that a place where light emitted from the LED hits can be confirmed. A visible light LED has a large variation in luminance and cannot be used as a light source for a bar code reader unless some control is added. Normally, the circuit shown in FIG. 2 sets the drive signal 61 to high, measures the amount of light while the LED is lit with an illuminometer (not shown), and controls the current flowing through the LED 63 with the variable resistor 62 to increase the brightness. The brightness of the bar code was adjusted to a predetermined constant brightness and used as a light source for a bar code reader. However, in this variable resistance adjusting method, the variable resistor 62 is provided on the surface of the housing of the handy terminal due to the configuration of FIG.
Cannot be exposed, the variation in luminance is adjusted in advance in the state of the substrate before assembling the pen-type handy terminal 60 with a built-in barcode reader. If a problem occurs after assembling, it must be disassembled again and readjusted, which is very troublesome.

[0003]

Therefore, in the above-mentioned prior art system, the operator selects a part and corrects the variable resistance (VR1) 6 in order to correct the variation in the brightness of the LED 63.
2, it is necessary to adjust the brightness of LED1 (63) to a certain range. The parts sorting operation depends on human hands and requires a lot of man-hours, and the adjusting operation requires skilled skills, and there is a possibility that an operation error may be involved. After the adjustment with the variable resistor due to the variation in the brightness of the LED 63, it is necessary to fix it with an adhesive so as not to be changed by vibration or dropping. However, the variable resistor 62
Changes in resistance with time, the resistance value changes, or the knob of the variable resistor turns due to vibration, drop, etc., and the resistance value shifts, the light amount of the light source for the barcode reader changes, and the This may cause a decrease in the reading rate.

[0004]

In a pen-type handy terminal with a built-in barcode reader, an LED drive circuit for adjusting the light amount of a barcode irradiation LED built in the pen-type handy terminal with a built-in barcode reader is provided. The LED drive circuit uses a pulse width variable control function (PWM) built in the CPU of the pen type handy terminal with a built-in bar code reader to set a duty ratio for determining the length of the LED lighting time in the control program, and The present invention proposes a method of adjusting the light amount of a barcode irradiation LED in which a pulse width is varied by a control program.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The LED drive circuit configuration utilizes a PWM function built into a CPU. The PWM function is an abbreviation of Pulse Width Modulation, and is a function that can arbitrarily change the output of a pulse width generated from a CPU from 0 to 100%. For example, in the case of a low-brightness LED, the duty ratio (FIG. 5) is increased (to increase the ON interval) in order to extend the lighting time, and conversely, in the case of a bright-brightness LED, the duty ratio is reduced to shorten the lighting time. Is set in a small program (to shorten the ON interval).

[0006]

In other words, the pen-type handy terminal with a built-in barcode reader constructed as in the present invention adjusts the amount of light by adjusting the amount of light without using a variable resistor for adjusting the brightness of the light source LED for irradiating the barcode. Control within a certain range.

[0007]

First, an LED 2 (12) used in the pen-type handy terminal with a built-in bar code of the present invention is used to measure the range of the variation in the amount of light as shown in FIG. Generally, the commercially available LED 2 (12) emits light efficiently when a current of about 10 to 20 mA flows. In this case, since the lamp is turned on by pulse driving, the CPU 3 provided in the pen-type handy terminal body with a built-in bar code reader runs out of control, or even if the program has a bug and the duty ratio of the pulse collapses and the lamp is fully lit (duty ratio 100%), the LED 2 is turned on. (12) is set to 15 mA which does not destroy. (15m when the duty ratio is 50%
If it is set to A, even if all the LEDs 2 (12) are turned on, 30
Damage to the LED at mA is avoided. ) LED1
Then, a current of 15 mA is passed through 2 and the sample is turned on, and the luminance of 100 samples is measured with an illuminometer. Next, the range of the luminance variation is determined. The resistors used in the circuit have a general resistance accuracy of ± 5%, so they are used with ± 5%, so even if the brightness is adjusted with an accuracy of ± 5% or less. There is no point in increasing costs. The brightness of LED2 (12) was determined to be an appropriate value within ± 5% when measured with an illuminometer.

Next, a description will be given with reference to the block diagram of FIG. Reference numeral 1 denotes a flash ROM in which a program for adjusting the brightness of the LED is registered. Reference numeral 2 denotes a RAM, which responds to a command from the CPU 3.
Reference numeral 4 is a full graphic LCD as a display device
In this case, various displays are provided to an operator (not shown).
The barcode reader 5 is provided with the flash ROM 1 or RAM.
2 is a reader unit for storing information from a bar code (not shown). Reference numeral 6 denotes a key input unit, which is provided for inputting numerical values and codes that need to be input, and business selection. The calendar function 7 controls the date and time function of the main body of the handy terminal. Reference numeral 8 denotes a main battery, which supplies power for driving the above-described components. Reference numeral 9 is a sub-battery,
This is provided to support the main battery when the capacity of the main battery 8 is exhausted.

Next, a description will be given with reference to FIG. The CPU 3 has a performance of about 16 bits and has a built-in PWM function and ADC function. The light emitting circuit for irradiating the bar code has a resistor R4 for limiting the current.
Through a PWM port 11 provided in the CPU 3 via the. Barcode (not shown)
The circuit that receives the light irradiated with is a photodiode (FD1) that detects light, an amplifier (AMP1) that amplifies a signal detected by the photodiode (FD1), a low-pass filter (LPF1) that cuts high-frequency noise, and a low-pass filter. ADC for analog-to-digital conversion in order for CPU3 to read the signal passed through (LPF1)
It is composed of port 13. Next, L
An initial value of the luminance of the ED 12 is set and stored in the flash ROM 1. The LED driving frequency shown in FIG.
The duty ratio of the pulse width is set to 50% at KHz. The basis for determining the initial value of the LED driving frequency as 100 KHz and the duty ratio of the pulse width as 50% is based on the fact that a low-pass filter is generally provided after the amplifier circuit of the light receiving element (not shown) provided in the bar code reader 5. 14 is built in, and the pen-type bar code reader is a manual operation, so that a normal bar code can be read if a frequency of 5 KHz (when the bar code is read with a resolution of 0.1 mm and a scanning speed of 1 m) can pass. . 10KHz low pass filter (LPF1) to pass 5KHz signal
is necessary. 10KHz low pass filter (LPF
1) When a pulse signal having a frequency faster than 10 times the frequency of 14 passes through the low-pass filter 14, it is almost attenuated, and the signal becomes LE
The drive pulse of D2 (12) does not wrap around, and the problem is eliminated. Therefore, the driving frequency of LED2 (12) was determined to be 100 KHz.

In accordance with the operation of the circuit shown in FIG.
The procedure for correcting the variation in luminance of D2 (12) will be described. When the pen-type handy terminal 60 (see FIG. 1) is started, a brightness adjustment program registered in advance in the flash ROM 1 is executed, and an initial setting value of 100 KHz,
A pulse having a duty ratio of 50% (see FIG. 6) is generated, and the LED 2 (12) is turned on. At this time, if the amount of light emitted from the tip of the bar code reader 5 is measured by an illuminometer (not shown) and exceeds an appropriate value, a predetermined key 2 (60) of the key input unit 6 determined in advance by a program. ) To gradually reduce the duty ratio,
As shown in FIG. 5, adjustment is made so as to fall within an appropriate value as in (50% to 40%, 30%). Conversely, if the value falls below the appropriate value, the key 1 (60) of the key input unit 6 determined in advance by the program is operated to gradually increase the duty ratio (50 as shown in FIG. 6). %
60%, 70%). When the range of the LED brightness is within the appropriate value from the beginning, it is not necessary to adjust the duty ratio.

[0011]

As described above, according to the present invention, L
It is no longer necessary to adjust the variable resistor to correct the variation in the brightness of the ED, and when a problem occurs, it is no longer necessary to disperse or reassemble, thereby reducing man-hours.
At the same time, the need for a variable resistor was eliminated, and the resistance value did not change even when dropped or vibrated, stabilizing the barcode reading rate and contributing to quality improvement.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional pen-type handy terminal.

FIG. 2 A conventional LED drive circuit

FIG. 3 is a configuration diagram of a pen-type handy terminal with a built-in barcode reader.

FIG. 4 is a block diagram of a light emitting unit / light receiving unit.

FIG. 5 is an explanatory diagram of a duty ratio.

FIG. 6 is an explanatory diagram of a drive pulse and a duty ratio.

FIG. 7 is an explanatory diagram of a duty ratio when brightness is reduced.

FIG. 8 is an explanatory diagram of a duty ratio when brightness is increased.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flash ROM 2 RAM 3 CPU 4 Full graphic LCD 5 Barcode reader 6 Key input section 7 Calendar function 8 Main battery 9 Sub battery 10 Pen-type handy terminal 11 PWM port 12 LED 13 ADC port 14 Low-pass filter

Claims (1)

[Claims] 1. A pen-type handy terminal with a built-in barcode reader, wherein the barcode irradiation LE built in the pen-type handy terminal with a built-in barcode reader is provided.
In the LED driving circuit for adjusting the light amount of D,
The drive circuit uses a variable pulse width control function (PWM) built into the CPU of the pen-type handy terminal with a built-in bar code reader to set a duty ratio for determining the length of the LED lighting time in the control program, and to perform the control. A method for adjusting the light amount of a barcode irradiation LED, characterized in that a pulse width is varied by a program.