At present, the LED display has a breakthrough in both color and size, and the color can achieve full color coverage, and the size can also be made into hundreds of square meters, and the display dimension can be comprehensively improved.
1, the classification of LED display
1.1 Classification by usage environment
According to the use environment can be divided into indoor led display and outdoor led display . The indoor led display features large viewing angle, moderate screen brightness, high density, light weight and suitable for close-up viewing. The outdoor LED display features high color mixing distance, high screen brightness, waterproof and UV resistance.
1.2 Sort by display function
Press the display can be divided into graphic led display screen, video LED display, digital display. The characteristics of the graphic LED display screen can display pictures and text information, and can be displayed offline. The video LED display features 2D or 3D video information such as live broadcast, video, video, etc.; digital display device It is a 7-segment digital tube, mainly used for displaying digital electronic screens, electronic clocks, and so on.
1.3 Sort by display color
According to the display color, it can be divided into single primary color display, dual primary color display, and full color display. The single primary color led display is composed of a color LED and the like, and can only display one color; the double primary color led display is composed of red and green two color led lights , and the 256-level dual primary color LED display screen can display up to a large number of colors. 65,536 kinds; full-color display is composed of red, green and blue LEDs, and the 256-level full-color LED display can display up to 16,777,216 colors.
1.4 Classification by display
According to the display mode, it can be divided into page turning display, horizontal scrolling, static and vertical scrolling, and the like.
1.5 Classification by control
According to the control method, it can be divided into synchronous mode and asynchronous mode. The synchronous display mode is equivalent to using the LED display as a monitor of the computer, and realizes the display capability of multi-gradation by pointing the mapped computer image on the corresponding monitor; the asynchronous display mode utilizes the storage function and the automatic play function of the LED display itself. When the edited text and picture are transferred to the LED display on the computer, it will be played automatically. This method is generally only used to display text information due to the lack of multi-gradation display capability.
2, LED display design
2.1 LED display design principles
The principles that LED displays should consider include: reliability, compatibility, usability, cost performance, and more. The effect of reliability is that the software and hardware of the whole system can run stably, ensuring no leakage and smooth progress in daily information display. Compatibility mainly means that the system can normally access the computer and various video signals. The network content is displayed normally; the practicability mainly refers to the requirements that can be applied to various conditions and can satisfy the display information of graphic information, video, and official documents.
2.2 LED display design
2.2.1 Design of the display driver circuit
The display driver circuit is generally located behind the display screen to form a PUB board. The display driver circuit controls the information that needs to be displayed, and can be displayed to the display screen according to certain timings and rules; and the corresponding driving current and level are provided for the LEDs on the board, so that the display screen can display data, patterns, videos, and the like as desired. Text and other content.
The design of the display driver circuit is to use "row lighting, column scanning", that is, placing LEDs on the dot matrix module at the intersection of the column lines and the row lines.
The connection form between the modules is determined by the scanning method, and the scanning mode is divided into 1/16, 1/8, 1/4, 1/2, 1/1, and the like. The meaning of 1/16 is to refresh one line at a time, one scan period is 16, one control signal needs ABCD four; 1/8 is one line at a time, one scan period is 8, the control signal needs ABC; one analogy can get 1/4, 1/2, 1/1 scan period and control signal. 1/16 scan brightness is higher than 1/8, so 1/4 scan is generally used under intense illumination, and 1/16 scan is generally used indoors.
Selecting the driver circuit chip is also a very important task. The driver circuit chip can be generally divided into a power amplifier chip, a decoding chip, a row driver tube, an LED driver chip, and the like. The principle of selecting a power amplifier chip is to strengthen the control signal that is too low due to too many series connection of the dot matrix display module. The amplification power is generally 74HC245; the principle of selecting the decoding chip is: serial transmission is required. The signal is decoded to transmit the lighting signal to the display template, generally selecting 74HC138; the principle of selecting the action drive is to select the action drive capable of withstanding the large current of the display line, generally 4953; the principle of selecting the LED drive chip is to select A suitable LED driver chip provides enough current and matching level for the LED. The model selection is generally 8-bit 74HC595, 16-bit A6282 or TB62726.
The design principle of the PCB board is to install matching soldering holes on the front side of the PCB board, which is a combination of the PCB board and the display screen.
2.2.2 Design of the display panel
The display panel is further spliced ​​by a plurality of independent dot matrix display modules, and each dot matrix display module is composed of a plurality of light emitting points. In the monochrome dot matrix display module, each light emitting point is generally Corresponding to a light-emitting diode; in the color dot matrix display module, each light-emitting point is more complicated in composition, and can be composed of light-emitting diodes with different colors. After lighting different LEDs, the light-emitting points will be different. The color, the light point is the pixel point, the higher the pixel means the more pixels of the display panel, the higher the display resolution.
In the room, the display generally adopts 8*8 display module, and the other is that the pixel density is 64 pixels; in the outdoor, the dot matrix display module used in the display is not fixed, and the material is relatively flexible, generally speaking, It can be customized according to the needs of the user, and can also choose the appropriate brightness and color that the designer needs.
2.2.3 Control Computer
The core of the display system is the control of the computer. The designer controls the computer and transmits the digital, image, text, video and other information that he wants to display to the display circuit, and can provide control ideas. The control signals sent by the control computer generally have an EN enable signal, a CLK clock signal, an STB latch signal, an RI data signal, and an ABCD line signal.
The EN enable signal can control the signal on the whole screen, or blank the display, and adjust the appropriate duty cycle by changing the EN enable signal;
The STB latch signal transmits the data in the register to the latch and then illuminates the data through the driver circuit. However, since the driver circuit is controlled by the enable signal, the premise of lighting must be that the flat configuration is on. State, the latched signal also needs to be coordinated with the clock signal to display a neat image;
The RI data signal can provide the transmission data needed for display. The working principle is to coordinate with the clock signal, and then transfer the data to the display point that you want to display. When the data is not equal, the corresponding color display will be abnormal;
The ABCD line signal exists in the dynamic scanning stage. The meaning of ABCD is four binary, the ABCD signal four-way line signal is 16 lines, the ABC three-way line signal is 8 lines, and so on.
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