LED display control system (LED Display Control System), also known as an LED display controller, LED display control card. It is the core component of the LED display. It is mainly responsible for receiving the picture and video display information from the computer serial port or DVI interface, placing it in the frame memory, and generating serial display data that can be recognized by the LED display according to the partition drive mode. and scan control timing.
Through the analysis of the dot matrix module and the control circuit, the components of the LED display screen are determined; through the analysis of the single chip microcomputer and the intelligent control module, the composition structure and scanning driving mode of the LED display screen are determined to realize the display of the LED display screen.
According to the application of the LED display control system, the architecture and workflow of the LED graphic displays are designed. Among them, the software system and the wireless transmission control hardware main system use serial communication to complete the program download and realize the transmission of text information.
1 Overall analysis of LED display control system
LED display system composition LED graphic display system consists of the software control system, wireless transmission system, equipment main controller, LED display dot matrix, power supply, and other parts.
System working process: The main tasks of the software control system are graphic editing, font extraction, and saving, image preview, and file transmission; the wireless transmission system mainly completes the transmission of file information from the PC to the LED display, and the LED dot matrix in the hardware control system is mainly used. The task is to complete the information display through current control, drive the LED dot matrix row and column through the control of the scanning driving mode of the single chip, realize the driving of the device and finally realize the received graphic and text display function.
2 Analysis and design of computer software modules
The software module is divided into an editing part and a control communication part. The editing part realizes the editing function of graphic files, and the communication part completes the transmission of files to the single-chip memory module through RS-232C serial communication. The communication part will be introduced in detail in Chapter 3. The system design adopts the Windows operating system, and the text editing window is opened. The pixels in the client area are the same as those of the actual LED dot matrix display. The functions are similar to Word document editing tools, including editing modules, drawing modules, text editing modules, and color control. module, display effect loading module, preview module, and an information download module.
2.1 Editing modules
1) In addition to the self-generated cut, copy, and paste functions of Windows, the system has added the functions of undo and repeat.
first. Select the undo function to realize the step-by-step cancellation function of the previous editing work. Then, select the repeat function to realize the most recent operation command of the previous editing work.
2) Drawing: Graphic drawing functions including lines, rectangles, ellipses, circles, etc.
3) Text editing: including text editing of various fonts, shapes, font sizes, effects, and colors, and adding text editing at specified locations according to the special purpose of the application.
First, select the text function, the font selection box will pop up, and you can select the text of various fonts for editing. After that, call up the specific text position editing dialog box, enter the text and the abscissa, and ordinate the required display position.
4) Color control module: Due to the specific characteristics of the application field, three colors of red, green, and yellow are mainly used, which can realize color control.
2.2 Add effect module: By adding display effect and single-screen transmission of multi-screen files in transmission communication, the functions of the control system are improved.
1) Normal effect, statically display the information on the screen.
2) The scrolling effect can realize the scrolling display of information from left to right and can be interspersed with static information.
3) Single-screen information transmission to realize the saving of edited information to be transmitted.
4) Multi-screen information transmission, realizes the edited and saved single-screen information is merged and saved into one file, which greatly reduces the cumbersomeness of file transmission.
2.3 Image preview module: realize the preview function of font information before file transfer, can preview any form of font information saved before the transfer, and directly integrate it into the toolbar file open function key button.
1) Display effect, through the preview before file transfer, you can adjust the order of static and scrolling display effects.
2) Display time, display the time interval between different screen display information.
3 LED display control technology
With the development and use of the fifth-generation “array” control system, the birth of this generation of control system has improved Yuanheng Optoelectronics’ technical advantages in screen control, and further improved the display signal processing technology. After using the “array” control system.
First of all, the frame-changing frequency of the display screen can be increased from the current 60Hz to above 120Hz, which is far greater than the resolution capability of human eyes, so that people can watch without any stroboscopic and water ripples, which improves the display quality.
Secondly, the gray level of the three primary colors of red, green, and blue on the display screen can be increased from the current 256 to 1024, which makes the color more vivid, the color reproduction better, and the displayed image more realistic.
Finally, the LDVS signal is used for transmission, which minimizes the loss of the signal, synchronizes the display content of the entire display, and improves the consistency of the display.
3.1 Energy-saving and consumption-reducing technologies
Due to the use of an array control system, it can effectively reduce the loss of display screen brightness caused by the control system used to generate grayscale. According to comparative calculations, the system loss of the traditional “centralized control system” is between 30% and 40%. , the system loss of the “array control system” is between 8% and 10%. The reduction of the control system loss is conducive to improving the brightness of the display screen or reducing the current of the display screen under the same brightness conditions, so as to achieve The effect of energy saving and consumption reduction. In the centralized control system, due to the large control range, in order to maintain a certain refresh rate, it is necessary to reduce the number of scans and reduce the brightness to form grayscale; due to the small control range of the array control system, the number of scans can be greatly increased, and the loss of brightness will follow. become smaller. The scan times of the array system can reach more than 136 fields, while the centralized type can reach up to 42 fields.
According to the principle of brightness loss, the calculation table is compared as follows: a 200-square-meter outdoor full-color display with 3906 dots/square meter, if a driving current of 20mA is used, the theoretical maximum brightness can reach 15000cd/m2, if it wants to reach 6000cd/m2 The maximum actual brightness of the display screen is 11.4mA/pixel, and the maximum power supply current is 607A; if the “array control system” is used, it can reach 6000cd/ The maximum actual brightness of m2, according to 10% system loss, the display drive current is 8.89mA/pixel, the maximum current is 474A, and the energy saving rate is 21.9%. The average power consumption is 40% of the maximum power consumption, every day Calculated according to 10 hours of use time and 300 days per year, the annual power consumption of the “centralized control system” is 160,248 kWh. The annual power consumption of the “array control system” is 125,136 kWh, saving about 35,112 yuan per year (calculated at 1.0 yuan per kWh)
3.2 Single-point detection technology
In order to improve the reliability of the screen and increase the convenience of maintenance, Yuanheng Optoelectronics has developed a single-point detection technology for the display. Usually, the detection of LED pixels before the LED display leaves the factory is through visual inspection (that is, the human eye sees whether it emits light according to the debugging program). Not high either. Now our company uses the single-point detection function of the screen body and only needs to run the corresponding program to judge the working state of the pixel, so as to repair it, which greatly improves the reliability of the screen body. At the same time, with the continuous development of LED display technology, super-large LED screens have emerged in the market. This type of screen is generally installed at a high position and has a long viewing distance, which brings inconvenience to the detection work of the display screen. The judgment of each pixel point can only be based on human judgment. After using the single-point detection function, the maintenance personnel can easily find the coordinates of the fault point and replace them quickly.
3.3 Single-point luminance and chromaticity correction technology
The problem of brightness and chromaticity uniformity of LED display screens has always been a major problem for the industry. It can only be improved by subdividing and filtering the LED color coordinates. As people’s requirements for LED displays are getting higher and higher, only subdivision and screening of LED color coordinates can no longer satisfy people’s critical eyes. It is achievable to comprehensively correct the display to improve chromaticity uniformity. of. First, the brightness and chromaticity at a certain level are inconsistent due to the differences in the LEDs themselves (for example: using the same current to light up two green LEDs in the same production batch, the brightness may vary by 30%, and the wavelength may There will be 10-15nm variation). Secondly, after a period of use, the blue LED will dim the most and the red will be the least, but the biggest problem is that the LED will dim differently after a period of time. Therefore, even if the consistency of the LED screen is perfect in the factory, as the LED dims, the consistency will be lost, and the inconsistency of the LED screen will be significantly discovered after three years of non-stop use. To this end, Yuanheng Optoelectronics uses the world’s advanced monochrome luminance and chromaticity correction technology (also known as luminance and chromaticity signature technology) to solve the problem of color inconsistency caused by inconsistent attenuation of LEDs of different colors.
In terms of display technology, LCD is a display screen composed of liquid crystals, and LED is a display screen composed of light-emitting diodes. Each pixel unit in the LED digital display is a light-emitting diode, and the monochrome LED display is generally a red light-emitting diode.
In recent years, domestic LED display technology has been further developed. my country’s LED display has occupied 80% of the global market. However, the development of LED displays is not in my country. To this end, LED manufacturers in the industry will actively develop and improve LED technology. The overall design of the LED display software control system determines the system operation process and completes the system software control function. According to the specific equipment communication requirements, serial port communication technology is adopted. By introducing the relevant knowledge of port communication and serial port communication protocol, the communication between the control system and the hardware equipment part is realized, and the text information transmission function of the LED display screen is completed. The technical control of LED displays is an important guarantee to determining the quality of the product.