LED display screens are widely used in industrial and mining enterprises, schools, shopping malls, shops, public places, etc. for graphic display, advertising, information release. This paper designs a display composed of four 16×16 dot matrix LED modules, which is controlled by a single-chip microcomputer to smoothly display any number of characters or graphic symbols. This circuit can be cascaded and extended by any number of 16×16. A display consisting of a dot matrix LED module.
1 circuit design
The control circuit is composed of AT89C51 single-chip controller. The display screen consists of four 16×16 dot matrix LED modules. Each 16×16 dot matrix LED module consists of four 8×8 dot matrix LED modules. Users can expand and expand according to their needs. Any number of 16×16 dot matrix LED modules. 8 × 8 dot matrix LED module structure shown in Figure 1, a total of 8 rows and 8 columns, each LED placed at the intersection of the row and column lines, a total of 64 LEDs. When a column is high and a certain behavior is low, the corresponding LED is lit.
The P3.0 pin of the MCU is serially connected to the serial data input terminal of the shift register 74LS164 (U10), 8 74LS164 (U10~U17) are cascaded, and the P3.1 pin is connected to 8 74LSl64 clock pulse input terminals. 8 74LS164 are connected to 8 latches 74LS373 (U18~U25), and the data output terminals of 8 latches are connected to the row lines of 4 16×16 dot matrix LED modules, each 16×16 dot matrix LED module. The line is independently controlled. P1. O is connected to 8 74LS164 (U2 ~ U9) clock pulse input terminal, P1.1 is connected to U2, U4, U6, U8 serial data input terminal, every two 74LSl64 (U2 and U3, U4 and U5, U6 and U7 , U8 and U9) cascade; U2 ~ U9 parallel data output termination of 64 16 × 16 dot matrix LED module 64 column lines. P1.2 is connected to the clear terminal of all 74LSl64, and P1.3 is connected to the latch control terminal of the latch. The designed circuit is shown in Figure 2.
2 Working principle
This circuit uses the serial communication port to work in mode 0, while using P1. O and P1.1 analog serial outputs for smooth display of LED display characters. Since the LED module is a 16×16 dot matrix, the character dot matrix is ​​also a 16×16 dot matrix, that is, each character is composed of 32 bytes or 16 words of data, and each word data determines that each column of LEDs is lit. Happening. The 16×16 dot matrix character data is obtained by the character dot matrix extraction software.
First, the single-chip microcomputer P1.1 serially outputs a binary bit "1", and sends a high level to the first column of four 16×16 dot matrix LED modules via four groups of 74LSl64, followed by P3. O serial output of the first column data of four 16 × 16 dot matrix LED modules, that is, the row data of Y1, Y17, Y33, Y49 columns, which are latched by 74LS373 and sent to the line of the LED display screen. The LED corresponding to the first column of the LED module lights up. The row data of each column is 1 word data, 4 columns have 4 word data, and the address of the first byte of each word data in the character dot matrix data table is different by 32. At this time, each LED module displays the first character of each character. 1 column. Then P1.1 serial output one bit "0", after 4 sets of 74LS164 shift, send a high level to the second column of 4 LED modules, and then by P3. O serial output 4 rows of 16 × 16 dot matrix LED module data, that is, Y2, Y18, Y34, Y50 column row data, after 74LS373 latched and sent to the LED display line, each time The LED corresponding to the second column of the LED module is lit, that is, the second column of each character is displayed. In this cycle, the LEDs corresponding to each column of each LED module are sequentially illuminated until the 16th column of each LED module is lit, that is, the columns of each character are sequentially displayed. As long as the time of each column alternately displayed is appropriate, using the visual persistence characteristic of the human eye, it appears that the 16 columns of LEDs are simultaneously lit, that is, the entire character appears to be displayed at the same time. Then, the display is sequentially scanned from the first column to the 16 columns, and this is repeated a plurality of times to ensure that the displayed characters have sufficient brightness.
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