1 Main composition of LED display screen (taking the more complex synchronous full-color screen as an example)
1. The metal structure frame is used to form an inner frame and carry various circuit boards such as display unit board or module and switching power supply
2. Display unit: it is the main part of LED display screen, which is composed of LED lamp and driving circuit. The indoor screen is the unit display board of various specifications, and the outdoor screen is the module box.
3. Scanning control board: the function of the circuit board is data buffer to generate various scanning signals and duty cycle gray control signals.
4. Switching power supply: change 220V AC into various DC to supply various circuits.
5. Transmission cable: the display data and various control signals generated by the main controller are transmitted to the screen body by twisted pair cable.
6. Main controller: buffer the input RGB digital video signal, transform the gray level, reorganize it, and generate various control signals.
7. Special display card and multimedia card: in addition to the basic functions of computer display card, it also outputs digital RGB signals and line, field, blanking and other signals to the main controller. In addition to the above functions, multimedia can also change the input analog video signal into digital RGB signal (i.e. video acquisition).
8. Computer and its peripherals
Figure 1 LED display system composition
2 Analysis of main functional modules
1. Video broadcast
Through multimedia video control technology and VGA synchronization technology, various forms of video information sources can be easily introduced into the computer network system, such as radio and satellite TV signals, camera video signals, VCD video signals of video recorders, computer animation information, etc. Therefore, the following functions can be realized:
Support VGA display and display various computer information, graphics and images.
Support various input modes; Support pal, NTSC and other systems.
Display color video images in real time to realize on-site broadcasting.
Broadcast radio and television, satellite television and cable television signals.
Real time playback of video signals such as TV, camera and video disc (VCR, VCD, DVD and LD).
It has the function of playing pictures and words with different proportions on the left and right at the same time
2. Computer broadcast
Graphic stunt display function: it has the functions of editing, zooming, flowing and animation.
Display various computer information, graphics, images and 2D and 3D computer animation and overlay text.
The broadcasting system is equipped with multimedia software, which can flexibly input and broadcast a variety of information.
There are a variety of Chinese fonts and fonts to choose from. At the same time, you can also input English, Spanish, French, German, Greek, Russian, Japanese and other languages.
There are many broadcast modes, such as single / multiple line translation, single / multiple line up / down, left / right pull, up / down, rotation, stepless zoom, etc.
Editing, broadcasting and instant release of notices, announcements, announcements and news, and there are a variety of fonts to choose from.
3. Network function
Equipped with standard network interface, it can be connected with other standard networks (information query system, Municipal Publicity network system, etc.).
Collect and broadcast real-time data of each database to realize remote network control.
You can access the Internet through the network system
It has a sound interface, which can be connected to audio equipment to achieve audio-visual synchronization.
4. Screen controller
The screen controller controls the display effect of its corresponding display screen. It can automatically run a continuous cycle program to obtain relevant display data according to the given program list, or it can intervene manually to produce the display effect on the screen. The pixels on the screen are directly mapped with the pixels on the corresponding area of the screen controller display.
The screen controller can manually adjust the brightness of the display screen and select the gray nonlinear correction data suitable for the current environment. The screen controller can also automatically adjust the brightness of the display screen and select different gray nonlinear correction data according to the ambient brightness through the network system.
The contrast and chroma of image display can be adjusted through the screen control machine. The screen controller transmits the information to be displayed to the video processing and control unit for video processing.
5. Video processing and control unit
The video processing and control unit completes the image processing of the display data, including:
The second level of gray nonlinear correction can be adjusted automatically or manually.
Automatic or manual stepless brightness adjustment.
The gray level control system can control the display screen to display 24 bit data of 8 bits of each primary color, that is, 256 gray levels of each primary color.
Image noise reduction processing to ensure that the image is cleaner and smoother.
Image enhancement technology, image edge enhancement technology.
Motion compensation technology, chroma adjustment function.
6. Visual processing
In the system, the brightness of each primary color of a single module can be adjusted respectively, the color balance can be adjusted, and the mosaic phenomenon can be basically eliminated. The brightness consistency of all modules and display modules is good, and the monochrome display has no visual difference.
The video processing and control unit transmits the processed display information to the communication module for long-distance transmission to the display screen.
7. Communication module
The communication module ensures that the display content of the screen control machine is accurately transmitted to the display screen for a long distance. The communication module encodes and decodes the transmitted information, and processes the long-distance transmission and reception data. The communication module transmits the display information to the data distribution and scanning unit.
The LED display screen is usually composed of the main controller, the scanning board, the display control unit and the LED display screen body. The main controller obtains the color brightness data of each pixel of a screen from the computer display card, and then assigns it to several scanning boards. Each scanning board is responsible for controlling the dry lines (columns) on the LED display screen, and each line (column) The LED display signal on the is transmitted in series through each display control unit of the bank, and each display control unit directly faces the LED display body. The work of the main controller is to convert the signal of the computer display card into the data and control signal format required by the LED display screen. The function of display control unit operation is similar to that of image display screen. It is generally composed of shift register latch with gray level control function. However, the scale of video LED display is often larger, so we should use integrated circuits with larger integration scale. The function of the scanning plate is the so-called connecting link. On the one hand, it receives the video signal of the main controller, on the other hand, it transmits the data belonging to the current level to its own display control units, and also transmits the data not belonging to the current level to the next cascade scanning plate. The differences between video signals and LED display data in space, time, sequence and other aspects need to be coordinated by a scanning board.