Characteristics and scanning drive scheme of LED dot matrix display screen

Combined LED dot matrix displays have appeared since the 1980s. They use light-emitting diodes as pixels. They are made of high-brightness LED core arrays, epoxy resin and plastic mold packaging. They have the characteristics of high brightness, low power consumption, few pins, large viewing angle, long life, moisture resistance, heat resistance, and corrosion resistance.

There are two types of dot matrix displays: monochrome and dual-color, which can display red, yellow, green, orange, etc. LED dot matrix has 4×4, 4×8, 5×7, 5×8, 8×8, 16×16, 24×24, 40×40, etc.; according to the number of pixels, it can be divided into dual-primary color, tri-primary color, etc. The color of the text, image and other contents displayed is different according to the different pixel colors. The single-primary color dot matrix can only display fixed colors such as red, green, yellow and other monochrome. The color of the dual-primary color and tri-primary color dot matrix display content is determined by the lighting combination of different color light-emitting diodes in the pixel. For example, yellow can be displayed when both red and green are on. If the lighting time of the diode is controlled in a pulse manner, 256 or higher grayscale display can be achieved, that is, true color display can be achieved.

The internal circuit structure and appearance specifications of several LED dot matrix displays. The structure and pins of other types of dot matrix can be obtained through experiments. When a single LED dot matrix display is used, it can not only replace the digital tube to display numbers, but also display various Chinese and Western characters and symbols. For example, a 5 x 7 dot matrix display is used to display Western letters. A 5×8 dot matrix display is used to display Chinese and Western characters, and an 8 x 8 dot matrix is ​​used to display Chinese characters and can also be used for graphic display. A large-screen display can be formed by combining multiple dot matrix displays, but this type of practical device is often controlled and driven by a microcomputer or a single-chip microcomputer.

LED dot matrix scanning drive solution

From the internal structure of the LED dot matrix display, it can be known that the device should adopt dynamic scanning drive mode. Since most LED tube cores are high-brightness type, the single LED driving current of a row or column can be selected as narrow pulse, but its average current should be limited to 20mA. The forward voltage drop of the single LED of most dot matrix displays is about 2V. However, the forward voltage drop of the single LED of the dot matrix display with a bright spot of ∮10 is about 6V.

Large-screen display systems are generally composed of small modules composed of multiple LED dot matrices in a building block manner. Each small module has its own independent control system. After being combined together, only a master controller is introduced to control the commands and data of each module. This method is simple and easy to expand and maintain.

There are two display modes for each module in the LED dot matrix display system: static and dynamic. Static display has a simple principle and is easy to control, but the hardware wiring is complex. In practical applications, dynamic display is generally used. Dynamic display works in a scanning manner, driven by a narrow pulse with a large peak value, and selects each row of the display screen from top to bottom. At the same time, a pulse signal representing graphic or text information is sent to each column. By repeating the above operation, various graphic or text information can be displayed.