How to classify the LED display?

LED Display Control System (LED Display Control System) is a system that controls the correct display of LED large screens according to user needs. The online version is also known as the LED information release control system, which can control each LED terminal through the cloud system. The stand-alone version is also known as an LED display controller and LED display control card. It is the core component of the LED display. It is mainly responsible for converting external video input signals or onboard multimedia files into digital signals that are easy to identify on the LED large screen. , so as to light up the LED large screen equipment, which is similar to the graphics card in the home PC, the difference is that the display in the PC is CRT/LCD, etc., and the display in this system is the LED large screen. The access signal mode can be divided into synchronous systems and asynchronous systems.

 According to the way of display, the LED display system is divided into three categories
Graphic display system

Generally, the LED display screen that displays graphics and text is called a graphic screen. The main feature of the graphic screen is that each light-emitting device in the LED dot matrix is only on or off, and the strength cannot be controlled, which means that this type of screen has no gray-level control.

Image Display System

The image display screen is relative to the graphic display screen, which refers to those display screens with gray scales, which display more vivid pictures. The main feature of the image screen is to use limited grayscale and color modulation to display Images with less demanding color and grayscale requirements.

Video Display System

Based on the research on the skimming screen control system, the LED display screen that can receive the video signal and display the moving, clear, full-color image is called the video display screen.

According to the control method, we divide the display system into two categories
Communication Display System

The communication display screen is an asynchronous display screen. The asynchronous mode means that the LED screen itself has the ability to store and automatically play, and the edited text and non-grayscale pictures on the PC display information or the location code and picture of Chinese characters. number, etc., and various control commands are transmitted to the LED screen controller through the serial port or another network interface, call various data information pre-stored in the controller, process the received instructions into the dot matrix data required by the display screen as required, and publish to the on the display. Such screens generally have no multi-level grayscale display capability, and are mainly used to display text and simple graphic information, and can be multi-screen networked. This method must require a controller with a CPU to process the information.

The real-time mapping screen system

The real-time mapping screen is a synchronous display screen, the basic function is to realize the real-time mapping of the computer screen content of the LED display screen, including the display of Video video images with the support of the multimedia card. Take the data from the featured port of the host graphics card or the video master card to take out the data to be displayed after the graphics card has been processed, and then do certain processing to the data and send it to the LED display. This method can be realized without a controller with a CPU, or even just by making a hardware card.

The 256-level gray-scale LED display system can make the LED display screen display synchronously with the computer, and make it achieve a high-performance display effect. The 256-level grayscale LED display control consists of a multimedia card, a video controller, a long-line driver, a receiving card, and a display unit. The video controller obtains the digital display signal from the standard display interface of the multimedia card and converts it into the signal format required by the display screen. It can also obtain the control signal from the standard interface of the computer, and the user completes the control of the LED display screen through the computer software. Adjustments, and make the display screen can adapt to different specifications of multimedia cards, with a high degree of compatibility.

 From the way of communication classification
Wired communication

A communication method using tangible physical media such as cables and optical fibers as a medium. As far as the application is concerned, data transmission is generally carried out through a dedicated channel, which is expensive. It is believed that wired communication based on a public network will be more widely used in the future. Using the Internet to transmit data is also one of the main methods used by this system.

Wireless communication

The method of sending information from the monitoring center through radio waves between the LED screen controller and the monitoring center within the communication distance. This method saves system investment, shortens the construction period, and reduces the possibility of system theft. This communication method is similar to the form of a mobile phone short message using GSM, GPRS, or CDMA network for transmission, and also using broadcast towers, using FM or AM to transmit and receive signals.

Asynchronous control

LED display asynchronous control system is also called LED display offline control system or offline card. Mainly used to display all kinds of text, symbols, and graphics or animation. The screen display information is edited by the computer, and is pre-installed into the frame memory of the LED display screen through the RS232/485 serial port, and then displayed and played screen by screen, cyclically, and the display methods are colorful and varied. Its main features are simple operation, low price and wide range of use. LED display simple asynchronous control system can only display digital clock, text, and special characters. In addition to the functions of a simple control system, the biggest feature of the LED display graphic asynchronous control system is that it can control the content of the display screen by area. Support analog clock display, countdown, picture, table, and animation display. With timing switch, temperature control, humidity control, and other functions

Synchronous control

The LED display synchronization control system is mainly used to display video, graphics, notifications, etc. in real-time. Mainly used for indoor or outdoor full-color large-screen display. The LED display synchronization control system controls the working mode of the LED display is basically the same as that of the computer monitor. It maps the image on the computer monitor correspondingly in real-time at an update rate of at least 60 frames per second, usually with a multi-gray color display. Ability to achieve multimedia advertising effect. Its main features are real-time, rich expressiveness, complicated operation, and high price. A set of LED display synchronization control systems generally consists of a sending card, a receiving card, and a DVI graphics card.

LED full-color display control system
An array control system, LED full-color display control system

The “array” control system consists of the main control board, several sub-control boards, and several scanning boards installed in the display cabinet, which is equivalent to using a set of control systems in each cabinet for control. The structure fully improves the reliability and display effect of the display screen, and the effect is more obvious, which solves the problem of low frame changing frequency, insufficient gray level, and poor color uniformity when playing video on high-end LED displays. question. Appraised by the expert committee organized by the Science and Technology Bureau, the technology has reached the level of domestic leading and international similar products.

The birth of this generation of control system has improved Yuanheng Optoelectronics’ technical advantages in screen control, and further improved the processing technology of display signals.

After adopting the “array” control system, first of all, the frame changing the frequency of the display screen can be increased from about 60Hz to more than 120Hz, which is far greater than the ability of human eyes to distinguish, so that people can watch without any stroboscopic and water ripples. appears, improving the quality of the display.

Secondly, the gray level of the three primary colors of red, green, and blue on the display screen can be increased from 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.

Adopt technology
Energy saving

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 using 20mA driving current, the theoretical maximum brightness can reach 15000cd/m2, if it wants to reach the maximum actual brightness of 6000cd/m2, the “centralized control” is used. system”, according to 30% system loss, the display drive current is 11.4mA/pixel, and the maximum power supply current is 607A; if the “array control system” is used, the maximum actual brightness of 6000cd/m2 is reached, 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%.

Calculated the average power consumption is 40% of the maximum power consumption, calculated according to 10 hours of use time per day, 300 days per year, and the annual power consumption of the “centralized control system” is 160248 degrees. The annual power consumption of the “array control system” is 125,136 kWh, saving about 35,112 yuan/year (calculated at 1.0 yuan per kWh)

Single point detection

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. Using the single-point detection function of the screen, just run the corresponding program to determine the working state of the pixel, so as to repair, which greatly improves the reliability of the screen. 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.

Luminance and Chroma Correction

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, the world’s advanced monochrome luminance and chromaticity correction technology (also called: luminance and chromaticity signature technology) is used to solve the problem of color inconsistency caused by inconsistent attenuation of LEDs of different colors.

The point-by-point correction system is a comprehensive set of software and hardware systems that can measure and correct each pixel on the LED display. performance characteristics.

Technology Development Status

The back-end control of the LED display originally used a conventional control circuit. With the continuous improvement of control technology and the application of control chips, LED application-specific integrated circuits are generally used, which can control and adjust the grayscale and each pixel according to the characteristics of the LED display, which makes the display brightness and color effects have the same effect. Due to the technical level and cost and other reasons, LED control chip products are mainly in the hands of foreign countries. At the same time, there are also some manufacturers in China that develop and produce LED display control circuits, etc. However, due to performance factors, it will take time to popularize and use them.

In fact, for the LED display control system, the research of the controller is the core issue. The development of display technology provides a better display effect, and people like this information release method more and more because it greatly promotes the convenience of people’s lives, which in turn promotes the development of the controller. The content displayed is more and more abundant, which makes the controller move towards higher performance and a more flexible direction.

 In addition to the development of LED display technology itself, with the continuous progress of network technology and the need for practical applications, network-based and intelligent LED control technology has also developed a new momentum. LED displays present new challenges. Since the LED display control technology and network technology were originally independent of each other, it is necessary to combine the two to realize the network cluster control of the LED display, and develop related software and hardware that conform to the network system protocol and specification. There is a long way to go.

The core of the LED display control system is the display controller of the screen body, which is widely used in single-chip + DPS, industrial computers or embedded industrial computers, and single-chip + large-scale programmable devices. The research and development of the FPGA method will bring more development vitality to the display controller, because this method can construct a microprocessor inside it, and can integrate more off-chip devices into the chip.

Development trend

The use of optical transceivers and optical fibers as the communication medium is more advantageous than the additional lightning protection measures required for cable connection and the maintenance work caused by unreliable cables.

Based on the transmission characteristics of the network, it is convenient to remotely manage, maintain and upgrade a single LED display controller. The functions are also richer, more practical, and more secure. The cost of serial port mode will be high, and all the corresponding LED controllers cannot operate after a communication server fails.

The hardware adopts a programmable embedded platform to ensure its stability and flexibility. The hardware description language is used to construct the required 32-bit CPU, which not only ensures performance but also provides flexibility for future applications. The main frequency is at least 33M or even more than 66M. In addition, the device memory and non-volatile memory space should also be large enough (8-16M or more). While some single-chip microcomputers can also realize part of the network functions, but because of the slow speed and poor performance.

The software platform has network capabilities, needs to support TCP/IP protocol wireless communication capabilities, and supports GPRS, GSM, CDMA, or FM protocols. Operating systems are generally used and commonly used operating systems including VxWorks, uC/Oslo, Linux, WinCe, etc.

The control equipment has a network management system and supports WEB services, and the operator can use the browser to monitor and control remotely, and perform maintenance and fault diagnosis. When the communication fails, the maintenance personnel can use the notebook computer on the spot and use the network port and serial port for data extraction and diagnosis.