How to design Chinese characters for LED display

Time:2018-11-28 Views:164

LED screen as the leader of outdoor large screen, display performance with hd, rich color, high brightness, simple maintenance and other characteristics, favored by the market.And Chinese characters are one of the most commonly used characters.Below to show you the LED screen Chinese character design process and scheme.

LED display is a planar display screen composed of LED dot matrix module or pixel unit.It has the advantages of high luminous rate, long service life, flexible configuration, rich color and strong adaptability to indoor and outdoor environment.And widely used in public places such as buses, shops, sports venues, stations, schools, Banks, highways and other information dissemination and advertising.LED screen development is fast, this paper describes the basic principle, hardware composition and design, programming and debugging, Proteus software simulation and other basic links and related technologies based on AT89C51 microcontroller 16 x 16LED Chinese character dot matrix scrolling display.

Hardware circuit composition and working principle

This product USES AT89C51 microcontroller as the core chip circuit to achieve, mainly composed of AT89C51 chip, clock circuit, reset circuit, column scanning drive circuit (74HCl54), 16 by 16 led dot matrix 5 parts, as shown in figure 1.Among them, AT89C51 is a low-voltage, high-performance CMOS 8-bit microprocessor (commonly known as single-chip microcomputer) with a 4kB flash Programmable and Erasable Read OnlyMemory (FPEROM).The device is manufactured by ATMEL high-density non-volatile memory manufacturing technology, and the McS-5l instruction set of industrial standard is compatible with the output pin.Due to the combination of multi-functional 8-bit CPU and scintillation memory in a single chip, it can perform 1,000 write/erase cycles, and the data retention time is 10 years.It is an efficient microcontroller that provides a flexible and inexpensive solution for many embedded control systems.Therefore, AT89C51 chip is often used in the process of intelligent electronic design and production.The clock circuit is composed of 18 and 19 foot clock terminals (XTAI l and XTAL2) of AT89C5l, 12 MHz crystal oscillator X, capacitance C2 and C3, and adopts in-chip oscillation mode.The reset circuit adopts simple power-on reset circuit, which is mainly composed of resistance R, R2, capacitance C and switch K, and is connected to the RST reset input terminal of AT89C51, respectively.LED dot array display adopts a total of 256 pixels of 16 x 16 dot array, and the pin distribution of the dot array can be determined by multimeter detection of LED.

We connect the line bus to the I/0 port of the MCU, and then send the scanning code analyzed above into the bus, and we can get the Chinese characters displayed.However, if the row and column ports of LED lattice are all directly connected to 89S5 1 single-chip microcomputer, 32 I/0 ports are needed, which will cause the exhaustion of I/0 port resources, and the system has no room for expansion.Therefore, we only in the practical application of the LED lattice 16 lines directly the mouth and P2 in P0 port, as for the columns selected scanning signal is composed of 4-16 line decoder 74 hcl54 to select control, thus columns selected control only using the single chip microcomputer four I/O port, save a lot of I/O port resources, provides conditions for single chip microcomputer system expansion function.Considering the P0 mouth pull up resistors must be set, we use the 4.7 k Ω resistance as pull-up resistor.The basic process of Chinese character scanning display is as follows: after power on, due to the effect of resistance R and capacitance c1, the RST reset pin level of MCU is first high and then low, so as to achieve the reset;Later, in C, C3, X and SCM under the action of the internal clock circuit, single chip computer 89 c51 in accordance with the procedures set in P0 and P2 output interface and internal Chinese corresponding code level, to the LED dot matrix row line selection (high level), at the same time in P1.1, P1.2, P1.3, P1.4 interface output columns selected scanning signal (low level driver), so as to select the corresponding pixel LED, and use the persistence of vision characteristic of human eyes to synthesize the display of Chinese characters.Then change the table address to achieve scrolling display of Chinese characters.

2. Bitmap display principle of Chinese characters and code acquisition method of character base

We take the Chinese song font library of UCDOS as an example. Each word is displayed by a lattice of 16 rows and 16 columns.That is, each word in the national standard Chinese character database is represented by 256 dot arrays.We can think of each point as a pixel, and the glyph of each word as an image.In fact, the Chinese character screen can display not only Chinese characters, but also any graphics within 256 pixels.Such as check with 8-bit AT89C51 SCM control, because the SCM bus by 8-bit, a word needs to be split into two parts.

In order to find out the rule of Chinese character dot matrix composition, the code of Chinese character is obtained by column scanning method.Chinese characters can be divided into upper and lower parts, the upper part is composed of 8 * 16 lattice, the lower part is also composed of 8 * 16 lattice.In this example, the upper half of the first column in the upper left corner, namely P00 ~ P07 port of the 0th column, is displayed by column scanning method, and the direction is P00 to P07. When the Chinese character "I" is displayed, it is completely extinguished, and the lower half of the first column is also completely extinguished.The upper half of the second column, P06, lights up and is arranged from top to bottom: po.0, po.1, P0.2, po.3, po.4, P0.5, P0.6, P0.7.That is binary 00000010, converted to hexadecimal for 02h.After the completion of the second column of the upper half, continue to scan the second column of the lower half. For the convenience of wiring, we still designed to scan from the top down, i.e., from P27 to P20. As can be seen from figure 3, P23 of this column is bright, i.e. 00001000, while hex is 08h.According to this method, go to the third column, the fourth column..., until the scanning in the 16th column, 32 8-bit scanning codes of Chinese character "I" can be obtained:

　　00H，02H，08H，06H，28H，02H，24H，22H

　　0FCH，3FH，24H，2 1H，20H，10H，3CH，08H

　　0E2H，07H，20H，0AH，0E4H，11H，0A8H，20H

　　20H，30H，00H，00H，00H，00H，00H，00H

It can be seen from this principle that no matter what font or image is displayed on the LED screen, the scanning code can be analyzed in this way and displayed on the screen.Although the above method can make us clear the acquisition process of Chinese character dot matrix code, it is very tedious to obtain Chinese character code by manual method.For this reason, we often use the font library software to find character code, the software opens the input of Chinese characters, click "check", hex data of the Chinese character code can be automatically generated, we need the vertical data copied into the program.

It can be seen that Chinese dot matrix display generally has three kinds of scanning: dot scan, row scan and column scan.In order to meet the requirements of visual retention, the scanning frequency of the point-scanning method must be greater than 16 * 64-1 024 Hz with a period less than 1 ms.The scanning frequency of the row scanning and column scanning method must be greater than 16 * 8 -- 128 Hz, with a period less than 7.8ms. However, when driving one column or one row (8 leds) at a time, an additional driving circuit is required to increase the current, otherwise the LED brightness will be insufficient.

3 program design and debugging in Keil environment

The software program is mainly composed of start, initialization, main program and font library.

After programming, debugging and compiling in keil software, Hex files that can be run by MCU are generated.

4 Proteus software is used to simulate LED Chinese character display screen

Proteus is different from other SCM simulation software in that it can not only simulate the work of the peripheral circuit of SCM or other circuits without the participation of SCM, but also simulate the work of the CPU of SCM.Therefore, in the process of simulation and program debugging, the process and results of program running and circuit working are directly viewed from the perspective of engineering.In a sense, Proteus simulation is basically close to engineering application.This design based on AT89C51 microcontroller 16 x 16 led Chinese character scroll screen has been implemented by Proteus software simulation.

Although this design only USES a 16 * 16LED lattice, simple circuit, but has included the basic principle of LED Chinese character scroll screen circuit, basic program and Proteus software simulation, as long as the expansion of the 10 interface of microcontroller, and add some LED lattice and related chips, can design a larger area of LED display, more pattern.Therefore, this paper has certain theoretical and practical reference value for similar designs.

Chinese character scrolling of LED screen is one of the common ways of playing. As long as the IO interface of MCU is extended, the dot matrix of LED screen can be added. With the increase of LED dot matrix, the area of screen can be automatically increased.When designing Chinese characters, we need to make the most appropriate design for the area of the display screen.