Dot Matrix LED Display System
LED dot matrix display create a simple, easy to install, are widely used in various public places, such as motor vehicle stop, and advertising, as well as bulletin boards and so on screen. In this paper, can be used in an office outside of the bulletin boards and so on of the LED dot matrix display design. Notice the content can be updated at any time, to date real-time display of temperature and time, and with automatic brightness adjustment function. Taking into account the necessary components of Tesco, the design uses 8 × 8 matrix of LED modules, composed of 16 × 64 LED dot-matrix, indicating the Chinese to be determined, as well as the number of characters.
Part of a dot-matrix display
Program I: serial manner. In this way can be displayed at the same time 4 16 × l6 lattice eight characters or 16 × 8 dot matrix characters, characters or numbers. Each dot matrix display unit 16 by the 8 × 8 dot matrix LED display module, the selection signal decoder 74HC138, driver 74HC245, data 74HC595 shift register and drive line components, as shown in Figure 1. Display unit can receive controller (the main control circuit board) or on a display unit of the data module transmission down information and command information, and information and to order the data without any changes of information to send to the next level, show modules, it can be expanded to display more display units, used to display more content.
Figure 1 shows the logical structure of serial diagram
This program for the dot matrix display system, the more commonly used, the more commonly used devices, readily available. But it is a fatal drawback, and that is to refresh fast enough. If you want to drive 64 dot matrix display, GM will be more difficult for single-chip microcomputer 51, there a serious stagnation of the scintillation phenomenon. In addition, in order to achieve a text about the movement and speed adjustment and other functions will be to bring about more difficulties in software design.
Option II: parallel manner. Can latch chips to expand the IO port to control the LED matrix of 64 out the purpose of line. Programs use 74HC573 latch 16 to form a double buffer register 8, the drive LED dot matrix line out of the 8 groups, with 4 / 16 of the 74HC595 decoder 16 dot matrix LED scanning line. In each line to send data to the LED dot-matrix before the first data sent to the first class, respectively, 8 74HC573, and then the second-class delivery 8 74HC573 lock pulse, data points together with the output to the LED array, This approach avoids the data of the line sync problem. As a result of parallel data transmission speed faster than serial, so flashing characters solved the problem is, the text is also relatively easy to move around the control. To sum up, the final choice of the design of the program.
Display control part 2
Program I: stand-alone mode. The adoption of a single-chip microcomputer to control all functions, including dot-matrix LED display shows set, model set, the time to read, temperature testing, as well as with the host computer's communications. Control only a single-chip dot matrix display can be reduced so that the circuit and software design is also easy to implement. However, all features will be integrated, a single chip AT89S52 is not enough processing power. At this point, the microcontroller CPU has been significantly less than internal resources, will lead to poor system, not better performance.
Option II: master-slave mode. The use of the work of master-slave single-chip microcomputer to control the entire system. Which is used to control a single-chip LED dot matrix display, a single chip for the expansion of the keyboard, serial communication with the host computer, temperature measurement, the time to read and so on. Relative stand-alone work, the work of master-slave model with greater capacity and a clear division of labor, the pace of implementation has been greatly improved. Although the hardware circuit and software design requirements of a number of relatively high, but also to the main issues from the single-chip communications. However, in order to better achieve the performance indicators, the design of such programs.
Hardware circuit design
Circuit design of the system's overall hardware block diagram shown in Figure 2.
Figure 2 LED dot matrix display system block diagram
1 system master circuit
Master circuit system shown in Figure 3, the smallest is a single-chip system, plus expansion slot with a number of functional circuits, using the keyboard scan to determine the work and the completion of the relevant operation mode. Also includes a time chip circuit and temperature detection circuit, as well as with the host computer RS-232 interface circuit.
Figure 3 master circuit
The design of the DS1302 is a small trickle charge current of the circuit capacity, the main feature is the use of serial data transmission, power-down protection for the programmable power supply to provide charging functionality, and can turn off the charging function. DS18B20 is first-line digital temperature sensor; temperature measurement range of -55 ℃ ~ +125 ℃; temperature measurement resolution of up to 0.0625 ℃; its work in the remote power supply can be introduced, but also can be generated parasitic power; multiple DS18B20 can Parallel to the three or two online, CPU port line can be only one of many DS18B20 communications, less occupied port microprocessor can save a lot of wire and logic circuits. The above features make it ideally suited for long-range multi-point temperature detection system.
2 dot-matrix driver and control circuit
The circuit is mainly sent to the output of single-chip dot matrix data, through the expansion of latch chip I0 mouth to control the LED matrix of 64 line-side out. With this design is 74HC573 latch 16 to form a double buffer register 8, the drive LED dot matrix line out of the 8 groups, with 4 / 16 of the 74HC595 decoder 16 dot matrix LED scanning line. In each line to send data to the LED dot-matrix before the first data sent to the first class, respectively, 8 74HC573, and then the second-grade 8 lock 74HC573 send a pulse, the data sent to the LED dot-matrix all out.
The design of the software process shown in Figure 4.
Figure 4 LED dot matrix display software process
Circuit simulation and testing
1 dot matrix display simulation and debugging
Proteus7.2 is a commonly used single-chip simulation software, in many instances with the actual circuit simulation is very similar. In order to ensure that the actual circuit, as far as possible to achieve the desired effect, reducing, for many circuit modules of the simulation program. On the dot matrix display with the corresponding procedures to deal with design, with the use of Proteus and Keil uvision2 simulation, aimed at improving the whole system to improve the hardware and software solutions to improve system efficiency and stability.
In the dot matrix display their choice of the program, modify the program through continuous connection with the serial circuit and found it difficult to achieve subtitles serially shifted to right of the function to adjust the speed of mobile subtitles nor convenient. After analysis, decided to test parallel manner, the result is not found in this way the complexity of the circuit and program design to bring a lot of convenience to facilitate the realization of subtitles in particular about the speed of mobile and mobile settings. Circuit simulation of the system shown in Figure 5.
Figure 5 Proteus simulation circuit
2 machine test
The compiler-generated code to the HEX file to download flash in single-chip, all connected modules, LED dot matrix display will be the function of the realization of each test.
Required by the design of the display of Chinese characters, letters and numbers have been achieved, and can control the text and the speed of moving around. At the same time, temperature and time can be real-time display date and with the success of PC-line communications. Whole system's hardware production is simple and difficult is the software design. The system uses a parallel manner, and the use of master-slave single-chip microcomputer to control the entire system, so that software can be reduced in the preparation of the difficulty of achieving the function easily.
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