Circuit design of LED display screen

发表于2021-04-29

  1. 1. Its main components.. Including AT89C51 monolithic controller and a display including 4 LED modules of 16 points X 16 points, of which each LED module is 16 points X 16 points, and each LED module has 4 LEDs. The module is 8 points X 8 points, and the user can expand any other LED modules to 16 points X 16 points as appropriate. Like its name, the 8 dot X 8 dot LED module is composed of 8 rows and 8 columns. There are light-emitting diodes at the intersection between each row and column, there are 64 in total. Suppose there is a situation where one column is high and one column is weak, then this diode will emit light. Regarding the microcontroller, the serial input of its pins should be connected with the serial data input of the shift register. Under normal circumstances, 4 16 points X 16 points will be connected with the data input ports of 8 latches. In the dot matrix, the modules of each row exist independently.


    2. Circuit system anti-interference design


    In fact, the LED display screen will also be affected by some interference elements. Therefore, related work has set up a special circuit to identify the password, that is, before each data transmission, the encrypted data part is sent to Inform the received cryptographic circuit that it is necessary to open the data transmission path and allow the single-chip data to be accepted. Due to the lack of differences in the cryptographic channels, interference signals during operation will close the single-chip data-receiving port.



    3. Design of conventional drive circuit for LED display screen


    The design of LED display drive circuit is usually divided into two categories: dynamic scan drive and static latch drive. The dynamic scanning driving method includes sharing a group of four-row, eight-row, and sixteen-row light-emitting diode column drive registers on the display screen, and these column drive registers are distributed on the line drive tube according to time. Therefore, the electrode line of each lighting space is equivalent to 1n of the total lighting time. Assuming that the refresh rate of each line exceeds 50 Hz, the visual persistence effect of human eyes can be used to see intact text or images. Conventional drive circuits are usually designed to use serial input and output general integrated circuit chips (such as 74HC595 or MC14094) as column locking, and low-power N-PN transistors such as 8050 as column control.


    4. Design of constant current drive circuit for LED display screen


    In a directional current operating range, its illumination is roughly proportional to the current passing through it, and belongs to a current control device. Therefore, as long as the current circulating in each LED light-emitting tube is constant, you can... the brightness of each LED light-emitting tube. The operating criterion of the conventional drive circuit indicates that the current cannot be controlled because its rows and columns are operating in a saturated state. For example, the fluctuation of the additional power supply voltage, the change of the pressure drop of the line scan drive tube, etc., will affect the current composition of the LED light-emitting tube, and cause its brightness to change. As long as the column drive tube changes from a saturated state to a linear amplification state, the irregularity of the screen brightness caused by these elements can be eliminated.


    This constant column current driving method can reduce the pressure of the line drive tube, and can change the DC power supply voltage without being affected by the number of times the LED tube is illuminated in a row. The brightness uniformity of the LED display is obtained by the constant current circulating in each LED light-emitting diode.