This article takes you through how LED displays work

阅读中文   Read in English   Lire le Français    Leer Español    Leer  Español - México   Membaca Indonesia   日本語を読む   قراءة العربية

The display system consists of four parts: computer, communication, control circuit and display drive circuit

Display part:

The display screen is assembled from several rows of display boards with uniform specifications and sizes. This part consists of display module, drive circuit, power supply and so on. Due to the different color mixing distances of light-emitting pixels of different sizes, and the required brightness of different illumination environments, the correct selection of the display part plays a decisive role in the display effect.

Control section:

The data transmission of each screen must pass through a dedicated communication card. The communication card is responsible for communication with the host, and sends the instructions from the host to the display screen in sequence according to the pre-arranged display and change order. The communication card adopts serial transmission.

Host part:

The control computer is the head of the whole system, and its performance is directly related to the accuracy and speed of data processing. The computer can be connected with the display screen through a special communication line, and the programmed information can be sent to the display screen for display. If you need to change the data in special circumstances, you can continue other work. And one computer can control several graphic screens and strip screen systems.

The basic working principle of LED display is dynamic scanning. Dynamic scanning is further divided into row scanning and column scanning. The commonly used method is row scanning. The line scanning mode is further divided into 8 line scanning and 16 line scanning.

In the line scan mode, each LED dot matrix chip has a set of column drive circuits, and there must be a latch or shift register in the column drive circuit to latch the font data of the content to be displayed. In the line scan working mode, the row control pins of the same name of the same row of LED dot-matrix chips are connected in parallel on one line, a total of 8 lines, and finally connected to a row driver circuit; there must also be a row driver circuit in the row driver circuit. Latches or shift registers used to latch line scan signals.

The control process of the single-chip microcomputer to the LED display is to read first and then write. According to the arrangement order of the LED dot-matrix chips on the screen, the single-chip microcomputer first drives the latches of the first LED dot-matrix chips in the first row to write the font data read from the external data memory, and then writes the font data read from the external data memory to the second chip. , 3rd slice until the last slice of this row has finished writing the font data, the single-chip microcomputer then writes the line scan signal to the row drive latch of this row, so the first row and the 1st row are related to the font data. The diode lights up. Then the 2nd row 1st row, the 3rd row 1st row until the last row 1st row lights up. After the first row of each row is lit, delay for a period of time, and then the screen goes black, so even if the single-chip microcomputer has completed the scanning control of one line of the LED display screen.

The scanning control of the 2nd line, the 3rd line of the LED display screen by the single-chip microcomputer until the 8th line of scan control, the process is the same as the scan control process of the 1st line. The control process of all 8 lines is completed, and the LED display screen also completes the complete display of 1 frame of image.

Although according to this working method, the LED display is lit line by line, and only one line is lit each time, but as long as each line can be lit more than 50 times per second, that is, the refresh frequency is higher than 50 Hz, then due to human The visual inertia, the image displayed by the LED display is still a full-screen stable image.