The Chinese character display is everywhere, and is widely used in car news stations, advertising screens, etc. The 16*16 LED display in this article is a combination of four 8*8 LEDs. The picture below shows the display of four 8*8 LEDs. (figure 1) Here I divide the circuit principle of the dot matrix LED display into two parts to introduce the display circuit and the display drive circuit. First, the display circuit I use a common cathode 8*8 dot matrix screen, which is relatively easy to buy on the market. The figure below is a physical map of the 8*8 dot matrix screen. (figure 2) There are two types of dot matrix screens, one is common cathode (left) and the other is common anode (right). The following figure shows two types of internal circuit principles and corresponding pin diagrams. (image 3) The display mode of the LED array is displayed line by line in the order of display coding. The display time of each line is about 4ms. Due to the persistence of human vision, it will be felt that 8 rows of LEDs are displayed at the same time. If the displayed time is too short, the brightness is not enough. If the displayed time is too long, it will feel flicker. This article uses low-level progressive scan, high-level output display signal. That is to say, the row signal is outputted to a low level, and only one row of LEDs is in a state that can be illuminated at any time, and the other rows are in an extinguished state. In order to facilitate debugging, the line signal scanning output pin and column signal display output pin of the 16*16 dot matrix screen composed of 4 8*8 are respectively led to the two sides of the display screen. The Protel schematic is as follows: (Figure 4) Si (i = 1, 2, 3, ..., 16) in the schematic shown in Fig. 4 represents the line scan signal output, and Di (i = 1, 2, 3, ..., 16) represents the column display signal output. The front and back of the physical circuit diagram are as follows: (Figure 5)
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January 23, 2020