JP2002055642A - Drive circuit for liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit, capable of directly driving a liquid crystal display with absolute minimum of components, without enlarging an mounting area even when a microcomputer, in which a liquid crystal display controller is not incorporated is used in this circuit. SOLUTION: In this drive circuit, the main point is to combine common signals for driving liquid crystal by timing outputs of a controller and the voltage division with resistors. This driving circuit is constituted of a microcontroller, a liquid crystal unit and pairs of voltage-dividing resistors which are interposed between the microcontroller and the liquid crystal unit. The port outputs of the mirocontroller output rectangular waves, whose phases each differs by π/4 (90 deg.), by being controlled by the internal program of the controller. Then, respective liquid crystal segments of a liquid crystal display are driven by the combination of common port outputs, which are to be obtained by dividing the voltages of rectangular waves each of whose phases differs by π/4 (90 deg.) with a set of the voltage-dividing resistors and output port outputs of the controller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a liquid crystal display, and more particularly, to a liquid crystal display used in portable small devices such as various hand-held measuring devices, hand-held medical devices, and hand-held health appliances. In the driving circuit.

[0002]

2. Description of the Related Art When a liquid crystal display is driven by a microcontroller, there are usually a method of mounting the liquid crystal controller as external hardware of the microcontroller and a method of using a microcontroller having a built-in liquid crystal display controller.

[0003] In general, in order to reduce the number of parts in an electronic device, to reduce the size of the electronic device, and to reduce the cost, a one-chip microcontroller is used. Therefore, the display section of the electronic device is operated by a liquid crystal display. When this is done, a microcontroller with a built-in liquid crystal display controller is usually used. However, most microcontrollers on the market do not have a built-in liquid crystal display controller, and microcontrollers with a built-in liquid crystal display controller have few models and limited choices, which limits the degree of freedom in circuit design. was there. On the other hand, the method of mounting the liquid crystal display controller as external hardware has problems such as an increase in the number of components, an increase in mounting area, an increase in production cost, and the like.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art. Even if the microcontroller does not have a built-in liquid crystal display controller, it does not increase the mounting area and minimizes the necessary size. It is an object of the present invention to provide a drive circuit capable of directly driving a liquid crystal display with the number of components.

Further, the present invention compares a microcontroller with a built-in liquid crystal display controller having the same performance with a microcontroller without a built-in liquid crystal display microcontroller. An object is to provide a drive circuit which is expensive but is advantageous in terms of cost.

[0006]

SUMMARY OF THE INVENTION A driving circuit for a liquid crystal display according to the present invention is based on synthesizing a common signal for driving a liquid crystal by a timing output of a controller and a resistance voltage division.

Therefore, a driving circuit for a liquid crystal display according to the present invention comprises a microcontroller, a liquid crystal unit, and a set of voltage dividing resistors interposed between the microcontroller and the liquid crystal unit. The output is controlled by an internal program of the microcontroller to output rectangular waves having different phases by π / 4 (90 °).

The driving circuit for a liquid crystal display according to the present invention also drives each liquid crystal segment of the liquid crystal display by a combination of a common port output and an output port output, and outputs π / 4 (9).
0 °), a common port output can be obtained by dividing the rectangular waves having different phases by a set of voltage dividing resistors.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a drive circuit of a half-duty liquid crystal display, FIG. 2 is a diagram showing an example of connection of a seven liquid crystal segment liquid crystal display, and FIG. FIG. 4 is a diagram showing the operation timing in the connection example, and FIG. 4 is a diagram showing the timing when the numeral 3 is displayed in the connection example in FIG.

As shown in FIG. 1, a driving circuit of a half-duty liquid crystal display is a microcontroller (MC).
U) 1, a liquid crystal unit (LCD) 2, and a set of voltage dividing resistors R1 to R4 interposed between the microcontroller 1 and the liquid crystal unit 2. The port outputs P1, P2, and P3 of the microcontroller 1 are controlled by an internal program of the microcontroller to be π / 4 (9
0 °), and outputs rectangular waves having different phases. Voltage dividing resistor R
1 to R4 have the same resistance value, and R3, R1, R2, R
4 in series. The output port P1 of the microcontroller 1 is connected to the open end of the voltage dividing resistor R3, the output port P2 is connected between the voltage dividing resistors R1 and R2, and the output port P3 is connected to the open end of the voltage dividing resistor R4. .

As shown in FIG. 2, the liquid crystal unit 2 generally has seven liquid crystal segments a to g for representing numbers.
And a liquid crystal segment M for representing a decimal point. The common port COM0 of the liquid crystal unit 2 is connected to liquid crystal segments c, e, g, and M, and the common port COM1 is connected to liquid crystal segments a, b, d, and f. The common ports COM0 and COM1 are also connected between the voltage dividing resistors R3 and R1 and between the voltage dividing resistors R2 and R4, respectively. Output port P4 of microcontroller 1 is connected to liquid crystal segments a and M, output port P5 is connected to liquid crystal segments b and c, output port P6 is connected to liquid crystal segments d and g, and output port P7 is connected to liquid crystal segment e.
And f.

Output port P of microcontroller 1
1, P2 and P3 are controlled by an internal program of the microcontroller and output rectangular waves delayed in phase by π / 4 (90 °), respectively. Output ports P1, P2, P
The output of the liquid crystal unit 2 is divided by the voltage dividing resistors R1, R2, R3, and R4.
Signal. Output ports P4, P5, P6 and P7 are
An arbitrary liquid crystal segment is driven or turned off by outputting a drive signal corresponding to the common ports COM0 and COM1 in synchronization with the operation timing under the control of an internal program of the microcontroller. This relationship will be further described with reference to FIG.

FIG. 3 shows the operation timing. Since the timings T1, T2, T3, and T4 are all equal,
1 to T4 (T1 + T2 + T3 + T
4) is equal to T1 × 4. Each of the output ports P1 to P3 outputs a predetermined voltage value V or 0 V (hereinafter, this voltage value relationship is represented as "1" or "0") at the following timings. a) At timing T1, P1 is "0", P2 is "0", P3 is "1" b) At timing T2, P1 is "1", P2 is "0", P3 is "0" c) Timing T3 , P1 is “1”, P2 is “1”, P3 is “0”. D) At timing T4, P1 is “0”, P2 is “1”, and P3 is “1”.

Thus, the common ports COM0, COM0
In FIG. 1, voltage values appear in the following relationship. a) At timing T1, “0” is set to COM0,
B) At timing T2, 1 / 2V is applied to COM0 and C
OM1 is “0” c) At timing T3, COM0 is “1” and CO
At timing T4, 1 / 2V is applied to COM0, and C is set to 1 / 2V.
"1" for OM1

At this time, the common ports COM0, COM1
When all of the liquid crystal segments a to g and M connected to the LED are turned on, the output ports P4 to P4
7 outputs a) “1” at a timing T1, b) “1” at a timing T2, c) “0” at a timing T3, and d) “0” at a timing T4. On the other hand, common ports COM0, CO
When all the liquid crystal segments a to g and M connected to M1 are turned off, the output ports P4 to P7 are set to “0” at the timing T1 and “0” at the timing T2, contrary to the above. c) At timing T3, "1" d) At timing T4, "1" is output.

When only the liquid crystal segments c, e, g, and M connected to the common port COM0 are turned on, the output ports P4 to P7 are a) "1" at the timing T1 and b) "0" at the timing T2. c) At timing T3, "0" is output. d) At timing T4, "1" is output. On the other hand, when only the liquid crystal segments a, b, d, and f connected to the common port COM1 are turned on, the output ports P4 to P7 are set to “0” at the timing T1 and b) at the timing T2, contrary to the above. , "1" is output at c) timing T3, and "0" is output at d) timing T4.

FIG. 4 shows the relationship between the timing when the liquid crystal display shown in FIG. 2 displays the number "3" and the output of each port.

Among the liquid crystal segments a to d and g for displaying the number "3", the liquid crystal segments g and c are driven at the drive timing of the common port COM0, and the liquid crystal segments a and d are driven at the drive timing of the common port COM1. b and d will be driven. By outputting the following voltage values to the ports P4 to P7 at the timings T1 to T4, the liquid crystal segments a to d and g can be driven. 1) "0" at timing T1, T2
To output "1", T3 to "1", and T4 to output "0", thereby turning on the liquid crystal segment a. 2) "1" at timing T1, T2
To output "1", T3 to "0", and T4 to output "0", thereby turning on the liquid crystal segments b and c. 3) "1" at timing T1, T2
To output "1", T3 to "0", and T4 to output "0", thereby turning on the liquid crystal segments d and g. 4) "0" at timing T1, T2
To output "0", T3 to "1", and T4 to output "1", thereby turning off the liquid crystal segments e and f.

Each port P at each timing T1 to T4 for each of the other numbers and the numbers with a decimal point
The description of the output relations 4 to P7 can be easily analogized from the above description for those skilled in the art, and is omitted to avoid redundancy.

[0021]

As described above, according to the present invention, a single rectangular wave is converted to π / 4 (9
0 °), the liquid crystal display is driven by creating four rectangular waves having different phases and using them in a predetermined combination. The liquid crystal display can be directly driven with the minimum necessary number of parts without enlarging, thereby making it possible to manufacture the liquid crystal display at lower cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a drive circuit for a half-duty liquid crystal display.

FIG. 2 is a diagram showing a connection example of a seven liquid crystal segment type liquid crystal display.

FIG. 3 is a diagram illustrating operation timings in the connection example of FIG. 2;

FIG. 4 is a diagram showing timing when a numeral “3” is displayed in the connection example of FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 Microcontroller (MCU) 2 Liquid crystal unit (LCD) a to g, M Liquid crystal segment COM0, COM1 Common port P1 to P7 Output port R1 to R4 Voltage dividing resistor

Claims (2)

[Claims] 1. A microcontroller, a liquid crystal unit, and a set of voltage-dividing resistors interposed between the microcontroller and the liquid crystal unit. The port output of the microcontroller is controlled by an internal program of the microcontroller to generate π. A driving circuit for a liquid crystal display, which outputs rectangular waves having different phases every / 4 (90 °). 2. Each liquid crystal segment of the liquid crystal display is driven by a combination of a common port output and an output port output.
2. The liquid crystal display driving circuit according to claim 1, wherein the common port output is obtained by dividing a rectangular wave having a different phase by π / 4 (90 °) by the pair of voltage dividing resistors.