JP3048811B2 - Automatic contrast adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly to an automatic contrast adjusting device capable of automatically adjusting the contrast of a liquid crystal display screen.

[0002]

2. Description of the Related Art Many information processing apparatuses such as personal computers employ a liquid crystal display (hereinafter, referred to as an LCD) as a display from the viewpoint of miniaturization and power saving. This LCD is generally provided with a contrast volume, which can be manually operated to adjust the contrast to a desired state.

However, since the display density of an LCD is generally high at low temperatures and whitish at high temperatures, in the above-described apparatus, the contrast must be adjusted by operating the volume according to the temperature rise accompanying use. Must.

[0004]

In order to solve such a problem, there has been proposed an apparatus in which the contrast is automatically adjusted according to the temperature. However, there is an individual difference in the question of whether or not the contrast is appropriate. When the contrast is adjusted according to a specific adjustment rule (that is, the temperature-driving voltage characteristic), the contrast is not necessarily optimized for all users. It cannot be adjusted. In addition, the LCD itself has some characteristic variations in manufacturing, and there is a problem that the contrast differs between LCDs even with the same driving voltage, and there is no means that can solve this. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide an automatic contrast adjusting device which can provide an optimum LCD contrast for each user's eyes.

[0006]

According to the present invention, in a liquid crystal display device for displaying various information with a contrast corresponding to a given drive voltage, a storage means for storing a characteristic table in which operating temperatures are associated with drive voltages. An operation switch for inputting and setting a drive voltage of the liquid crystal display device; a characteristic correction unit for correcting the content of the characteristic table based on the drive voltage set by the operation switch; and a temperature of the liquid crystal display device. And a liquid crystal driving means for reading out a corresponding driving voltage from the characteristic table based on the temperature data obtained by the temperature measuring means and applying the driving voltage to a liquid crystal display device, The correction means sets the correction amount of the drive voltage set by the operation switch at the temperature t to ΔVt, and is a positive integer that changes as 1, 2,. The correction amounts of the drive voltage at a low temperature (t-n-1) different by a predetermined amount and a high temperature (t + n + 1) different by a predetermined amount in accordance with the change of the number n are defined as ΔVt-n-1 and ΔVt + n + 1, respectively. , A as a constant,
ΔVt-n-1 = ΔVt + n + 1 = ΔVt + n−a / ΔVt = ΔVt
It is characterized in that the characteristic table is modified so as to satisfy -na / ΔVt.

It is preferable that the characteristic correction means corrects the characteristic until the characteristic after the correction crosses the characteristic before the correction.

Preferably, the characteristic correction means stores a constant a, and the value of a can be changed.

[0009]

According to the present invention, the content of the characteristic table is corrected in accordance with the adjustment amount manually input by the contrast switch, and thereafter, the contrast of the liquid crystal panel is automatically adjusted based on the characteristic table. In particular, since the characteristic around the temperature at which the adjustment amount is input is changed using the above equation, the contrast adjustment according to the magnitude of the constant a is performed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows an automatic contrast adjusting device and a liquid crystal display panel according to an embodiment of the present invention. In this figure, the LCD panel 11 is provided with four control terminals VDD, VEE, VSS and V0, respectively (+ 5V), (+ 38V), GND, and liquid crystal drive voltage (2
(6 V to 38 V). Then, various information is displayed with a contrast corresponding to the liquid crystal drive voltage V0. Also, on the side of the LCD panel 11,
A thermistor 12 having one end grounded and the other end connected to a power supply VCC via a resistor 13 is fixedly installed. The resistance value of the thermistor 12 decreases and increases in accordance with the rise and fall of the temperature of the installation site, and the potential VT at one end 15 (hereinafter referred to as a sensor voltage VT) increases as shown in FIG. It is to decrease with the. The sensor voltage VT is converted to a digital value by an analog / digital (A / D) converter 22 in the contrast control unit 21.
The data is input to a central processing unit (CPU) 23.

A dip switch 40 for outputting information indicating an LCD type such as STN monochrome / STN color.
The LCD type information 16 is read by the CPU 23 as 2-bit information at the first startup after manufacturing.

A read only memory (ROM) 24 and a writable and readable memory (R) 24
AM) 25 is provided. In the former, a characteristic table indicating the basic characteristics of the temperature versus the liquid crystal drive voltage V0 as shown in FIG. 3 is stored for each LCD type. This characteristic table actually associates the sensor voltage VT corresponding to the temperature data with the PWM (pulse width modulation) value corresponding to the liquid crystal drive voltage, and is provided in the RAM 25 or outside as necessary. Electrically rewritable memory (EEPRO)
M) 31.

The CPU 23 refers to a characteristic table in the RAM 25 based on the sensor voltage VT from the thermistor 12 and reads and outputs a corresponding PWM value. This PWM
The value is a PW of 1 KHz output from the CPU 23.
The count number CH during the high level period of the M pulse 33 (FIG. 4
(A)), and the CH decreases as the sensor voltage VT decreases (that is, the temperature rises). One cycle of the PWM pulse 33 is 250
Corresponding to the count, the count number CH is shown in FIG.
As shown in (b) and (c), values of “60” to “249” can be taken.

The PWM pulse 33 from the CPU 23 is converted to an analog voltage by a digital / analog (D / A) converter 32, and the analog adder 34 outputs the liquid crystal drive voltage M.
LCD is added to the reference voltage (+ 26V) which is the IN value.
It is supplied to the panel 11 as a liquid crystal drive voltage V0.

Also, contrast switches 38 and 39 are connected to the contrast control section 21 via an encoder 37, and these are manually and individually depressed one by one or continuously, as shown in FIG. , CPU23
The liquid crystal drive voltage V0 can be changed by changing the duty ratio of the PWM pulse 33 from the LCD. Here, the contrast switch 38 is used when increasing the liquid crystal driving voltage V0 to decrease the contrast, and the contrast switch 39 is used when decreasing the liquid crystal driving voltage V0 to increase the contrast.

The operation of the automatic contrast adjusting device having the above configuration will be described with reference to FIGS.

First, when a power switch (not shown) is turned on, the first start-up after manufacturing (step S101 in FIG. 5).
Y), the CPU 23 fetches the LCD type information 16 to determine the type of the LCD (step S102), reads the corresponding LCD characteristic table from the ROM 24, and
Write to EPROM 31 and RAM 25 (step S
103). On the other hand, when it is not the first activation (step S101; N), the characteristic table in the EEPROM 31 is read and written in the RAM 25 (step S10).
7).

The ROM 24 stores the revision number (revision) together with the default value of the characteristic table, and these are written in the EEPROM 31. Therefore, RO
By determining whether or not the M and the revision of the EEPROM 31 match, it is possible to determine whether or not it is the first activation after manufacturing.

Next, the CPU 23 takes in the sensor voltage VT from the thermistor 12, performs A / D conversion, and sets this value as a variable X (step S104). Then, based on the value of the variable X, the corresponding PWM value is read out by referring to the characteristic table of the RAM 25, and the PWM determined by this value is read out.
The pulse 33 is output (step S105). This PW
The M pulse 33 is converted into an analog voltage by the D / A converter 32, and the reference voltage (+ 26V) is added by the adder 34 to become the liquid crystal driving voltage V0 of the LCD panel 11.

Next, the CPU 23 sets "0" to the counter C and the accumulation variable Y (step S11 in FIG. 6).
1) In accordance with the following steps S113 to S118, a total of 16 pieces of temperature data (sensor voltage VT) are fetched four times per second for four seconds, and the average is obtained. That is, first, it is checked whether or not the contrast switch 38 or 39 has been pressed (step S112).
If not pressed (N; same), one sensor voltage V
T is fetched and A / D converted to obtain a digital value T (step S113). Then, the digital value T is added to the accumulation variable Y (step S114), and the counter C
Does not reach "15" (step S115; N),
C is incremented (step S116), and the process returns to step S112. Hereinafter, this processing is performed when the counter C is "1
Until 5 ″ is reached (Step S115; Y), a total of a total of 16 data is obtained, and an average value A thereof is obtained (Step S117).

Next, the average value A thus obtained is compared with the variable X (previous PWM value), and when A is larger than X (step S118; Y, step S119;
N), X is incremented by "1", and when A is equal to X (step S118; Y, step S119;
Y), X is not changed. On the other hand, when A is smaller than X (step S118; N), the magnitude of A is compared with that of (X-3), and the value of X is changed according to the result. That is, if A is smaller than (X-3) (step S121; Y), X is decremented by "1"; otherwise (step S121; N), the value of X is not changed. Then, the CPU 23 refers to the characteristic table of the RAM 25 based on the value of the
The M value is read, and a PWM pulse 33 determined by this value is output (step S105).

Such processing (steps S118 to S1)
By performing 22), even when the difference between the previous temperature data and the current temperature data greatly fluctuates, the value of the variable X (sensor voltage VT) when referring to the characteristic table changes by one. The liquid crystal drive voltage V0 also changes by the minimum step. In particular, when the temperature rises and the sensor voltage VT decreases, the liquid crystal drive voltage V0 is kept unchanged unless the sensor voltage VT decreases by 3 or more. Thereby, it is possible to effectively suppress the fluctuation of the contrast due to the automatic adjustment when the temperature fluctuation is large. In the above example, the value of the sensor voltage VT, which is the temperature data, is corrected. However, the PWM value obtained by referring to the characteristic table may be corrected by incrementing or decrementing. Of course, the effect can be obtained.

When the depression of the contrast switch is detected in step S112 (step S112; Y in FIG. 6), a manual input value from the contrast switch is fetched (step S131 in FIG. 7), and based on this value, Correct the PWM value at step (step S1)
32). Specifically, as shown in FIG. 4D, every time the contrast switch 38 is pressed once, the count number CH of the PWM pulse 33 in the high level period is incremented by one, and the liquid crystal drive voltage V0 increases. Then L
The display on the CD panel 11 becomes light. Conversely, each time the contrast switch 39 is pressed once, the count number CH is decremented by one, the liquid crystal drive voltage V0 decreases, and the display on the LCD panel 11 becomes darker. When the contrast switch is continuously pressed, the CPU 2
In step 3, polling is performed at a constant period until the depression of the contrast switch 38 or 39 is completed (step S133; Y), and the count number CH is incremented by 1 for the initial 4th count and 2 for the 8th count. The count is changed by counts, and thereafter by 4 counts.

Next, upon detecting that the contrast switch 38 or 39 has been released (step S133; Y), the CPU 23 resets the timer (step S13).
4) If the switch is not pressed again before elapse of 5 seconds thereafter (step S135; N, step S136;
N, step S135; Y), based on the PWM value obtained in step S132, the characteristic table in the RAM 25 is corrected (the correction method will be described later) (step S138), and this is written in the EEPROM 31 (step S138). S139), and returns to step S111.
On the other hand, if the switch is pressed again within 5 seconds after detecting the contrast switch off (step S13)
6; Y), reset the timer (step S13)
7), and return to step S111.

According to such processing, even when the contrast switch is operated by trial and error and the manual adjustment is performed, the characteristic table is corrected only when the final contrast state is reached. This is advantageous in that the life of an EEPROM having a limited number of times can be extended.

Next, referring to FIG.
A method of modifying the characteristic table in 138 will be described.

Now, the initial characteristic table is shown by a solid line 4 in FIG.
It is assumed that the characteristic shown in FIG. 1 is represented, and the current temperature is t. Here, assuming that the liquid crystal drive voltage V0 is reduced by .DELTA.Vt by operating the contrast switch 39, the temperatures (t-n-1) and (t +
The correction amount ΔV of the liquid crystal driving voltage in (n + 1) is calculated from the following equation (1). Here, n = 0, 1, 2,....

ΔVt−n−1 = ΔVt + n + 1 = ΔVt + n−a / ΔVt (1) where “a” is a temperature range to be corrected, that is, correction at a certain temperature is another A constant indicating the degree of effect on the temperature range, which is written in the EEPROM,
Settings can be changed.

In the equation (1), n is changed from 0 to 1,
The temperature (t-n-
The correction amount ΔVt-n-1 of the liquid crystal driving voltage in 1) and the correction amount ΔVt + n + of the liquid crystal driving voltage at the temperature (t + n + 1)
Calculating 1 gives, for example,

N = 0: ΔVt−1 = ΔVt + 1 = ΔVt−a / ΔVt (2) n = 1: ΔVt−2 = ΔVt + 2 = ΔVt + 1−a / ΔVt (3) n = 2 : ΔVt−3 = ΔVt + 3 = ΔVt + 2−a / ΔVt (4) Then, the characteristic curve data of (temperature vs. drive voltage) in the characteristic table is converted into the above equation (2), (3), etc. The processing is sequentially changed to the data obtained from, and such processing is performed until a new characteristic curve intersects the original characteristic curve. This allows
When the user changes the liquid crystal driving voltage by .DELTA.Vt by operating a switch at a certain temperature t, not only the liquid crystal driving voltage correction amounts (.DELTA.Vt-1, .DELTA.Vt + 1) on both sides but also the liquid crystal driving voltage.
Further, the amount of voltage correction around it is also changed.

As can be seen from equation (1), if a is made very large, the influence on other temperature zones of the table is reduced. On the other hand, when a is reduced, the influence is exerted over a wide temperature range. For example, when a = 0 is extremely set, the characteristic curve is shifted in parallel.

By performing the above-described characteristic table correction processing, new characteristic data, for example, as shown by a broken line 42 in FIG. 8, can be obtained. By performing such a manual adjustment at several temperatures, the original characteristic table is sequentially modified in a learning function into a characteristic table that matches the characteristics of the liquid crystal panel and is suitable for the user. Will be done.

As is apparent from the above equation, when the value ΔVt to be manually adjusted is large, the influence of the adjustment at one temperature on the other temperature zone becomes large, and when it is small, the adjustment at one temperature is small. The effect is small.

[0035]

As described above, according to the first aspect of the present invention, the contents of the characteristic table are modified according to the adjustment amount manually input by the contrast switch, and thereafter, the contents of the characteristic table are modified based on this characteristic table. The contrast of the LCD panel is automatically adjusted. Thereby, even if there is a characteristic variation between individual liquid crystal display panels and individual differences of users,
There is an effect that optimal contrast adjustment can be automatically performed according to the user's preference. In particular, it is possible to arbitrarily set the degree of the effect of the correction at a certain temperature on the amount of correction in another temperature zone according to the value of the constant a.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an automatic contrast adjusting device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing temperature characteristics of the thermistor in FIG.

FIG. 3 is a characteristic diagram showing contents of a characteristic table stored in a ROM in FIG. 1;

FIG. 4 is an explanatory diagram showing a waveform of a PWM pulse output from a CPU in FIG. 1;

FIG. 5 shows a CP in the automatic contrast adjusting device of FIG. 1;
9 is a flowchart showing the processing contents of U.

FIG. 6 shows a CP in the automatic contrast adjusting device of FIG. 1;
9 is a flowchart showing the processing contents of U.

FIG. 7 shows a CP in the automatic contrast adjusting device of FIG. 1;
9 is a flowchart showing the processing contents of U.

FIG. 8 is an explanatory diagram for explaining a method of modifying a characteristic table.

[Explanation of symbols]

 Reference Signs List 11 LCD panel 12 Thermistor 21 Contrast control unit 23 CPU 24 ROM 25 RAM 31 EEPROM 38, 39 Contrast switch

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/36 G02F 1/133 575 G02F 1/133 580

Claims (3)

(57) [Claims] 1. An automatic contrast adjusting device used in a liquid crystal display device for displaying various information with a contrast according to a given driving voltage, wherein a characteristic table in which operating temperatures are associated with driving voltages is stored. Storage means; an operation switch for inputting and setting a drive voltage of the liquid crystal display device; a characteristic correction means for correcting the contents of the characteristic table based on the drive voltage set by the operation switch; and the liquid crystal display device Temperature measuring means for measuring the temperature of the liquid crystal display, and a liquid crystal driving means for reading a corresponding driving voltage from the characteristic table based on the temperature data obtained by the temperature measuring means, and applying the read driving voltage to the liquid crystal display device The characteristic correction means sets the correction amount of the drive voltage set by the operation switch at the temperature t to ΔVt, and changes to 1, 2,. Positive integer is in response to changes in the variable n predetermined amount by different low temperatures (t-n-1) and respectively the amount of correction of the drive voltage in a predetermined amount by different high temperatures (t + n + 1) Δ for
Where Vt-n-1 and ΔVt + n + 1, and a is a constant, ΔVt-n-1 = ΔVt + n + 1 = ΔVt + n−a / ΔV
An automatic contrast adjusting device, wherein a characteristic table is corrected so as to satisfy t = ΔVt-na · ΔVt. 2. The automatic contrast adjusting apparatus according to claim 1, wherein the characteristic correcting unit corrects the characteristic until the characteristic after the modification crosses the characteristic before the modification. 3. The automatic contrast adjusting device according to claim 1, wherein the characteristic correcting means stores a constant a, and the value of the constant a can be changed.