Introduction to LED

LED display refers to LED digital tubes, LED dot matrix displays, etc., which are composed of light-emitting diodes. There are two commonly used types of LED light-emitting devices: digital tubes and dot matrix.

The display interface of LED display can be divided into two display modes: static display and dynamic display according to the driving method. The scanning of dynamic display can be completed by microcontroller software or special hardware. According to the way CPU transmits data to the display interface, it can be divided into two data transmission modes: parallel transmission and serial transmission.

· In static display, except for the period of changing the display data, each display is in the power-on display state, and the power-on duty cycle of each display is about 100%. The advantages of static display are stable display and high brightness; the disadvantage is that it occupies more hardware resources (such as I/O ports, drivers, etc.).

During dynamic display, N displays occupy one display data driver, and the power-on duty cycle of each display is 1/N. The advantage of dynamic display is that it saves hardware resources (such as LO port, driver, etc.); the disadvantage is that it takes up more CPU time when using software scanning, and compared with software scanning, hardware scanning will increase hardware costs. In addition, when the number of dynamic display bits is large, the brightness of the display will be affected.

The parallel transmission interface transmits display data in parallel, and its transmission speed is fast, but it occupies more I/O interfaces. The serial transmission interface transmits display data in serial mode, and its advantage is that it occupies less LO interface and has simple wiring, but its disadvantage is that the transmission speed is slow.

LED large-screen displays have been increasingly used in public places such as advertising, information release, and traffic instructions due to their eye-catching and flexible content, and have achieved good results. LED display screens are mainly divided into two categories: digital display and dot matrix display. This article only discusses dot matrix display.

In fact, no matter what the size of the display screen is, the principle is the same, so it is entirely possible to design a standardized, modular LED display screen. For different needs, you only need to randomly combine the corresponding modules.

This section introduces a modular LED display screen that can be flexibly changed in size as needed, can run independently of a computer, and can also achieve special effects such as flickering and scrolling. Since the refresh rate of the integral display screen is insufficient, flickering and other problems often occur. In this design, the display screen is divided into many small modules, thus solving the above problems.

7-segment light emitting diodes are referred to as LEDs (Light Emitting Diodes). They are a type of display device that displays segments. Seven LEDs form the seven-stroke character "8", and one LED forms a decimal point. The seven segments of the LEDs are called a, b, c, d, e, f, and g, respectively, forming the character "8". As shown in Figure (a), when a certain voltage is applied to a certain segment of the LED, some segments are lit up. If no voltage is applied, it will be dark. In order to protect each segment of the LED from damage, a current limiting resistor is required.

Figure 7 Segment LED display device