LED grayscale can also be called LED brightness. Gray level, also known as half-tone, is mainly used to transmit pictures. There are 16 levels, 32 levels, and 64 levels respectively. It uses matrix processing to process the pixels of the file into 16, 32, and 64 levels. layers to make the transmitted picture clearer. Whether it is a single-color, two-color, or full-color LED display, to display images or animations, it is necessary to adjust the grayscale of each LED that constitutes a pixel. The fineness of the adjustment is what we usually call grayscale.  

 

　　There are two ways to control the grayscale of the LED: one is to change the current flowing through it, and the other is pulse width modulation. 1. Change the current flowing through the LED. Generally, the continuous working current of the LED tube is about 20 mA. Except for the saturation phenomenon of the red LED, the grayscale of other LEDs is basically proportional to the current flowing; another method is to use the visual inertia of the human eye and use the pulse width The modulation method to achieve grayscale control, that is, to periodically change the light pulse width (ie, duty cycle), as long as the period of repeated lighting is short enough (ie, the refresh frequency is high enough), the human eye cannot feel that the light-emitting pixels are in jitter. Because pulse width modulation is more suitable for digital control, almost all LED display screens use pulse width modulation to control gray levels today when microcomputers are generally used to provide LED display content. The LED control system usually consists of three parts: the main control box, the scanning board and the display control device.  

 

　　

The main control box obtains the brightness data of each color of a screen pixel from the display card of the computer, and then redistributes it to several scanning boards, each scanning board is responsible for controlling several rows (columns) on the LED screen, and each row (column) The display control signal of the upper LED is transmitted in a serial manner.

 

There are currently two ways to serially transmit display control signals:

 

1. One is to centrally control the grayscale of each pixel on the scanning board. The scanning board decomposes the grayscale value of each row of pixels from the control box (ie, pulse width modulation), and then converts the turn-on signal of each row of LEDs in the form of pulses. (Light is 1, no light is 0) It is serially transmitted to the corresponding LED by row to control whether it is lighted or not. This method uses fewer devices, but the amount of data transmitted serially is larger, because in a cycle of repeated lighting, each pixel needs 16 pulses under 16-level grayscale and 256-level grayscale. 256 pulses, due to the limitation of the operating frequency of the device, generally only the LED screen can achieve 16-level grayscale.

 

2. One is pulse width modulation. The content of the serial transmission of the scanning board is not the switching signal of each LED but an 8-bit binary gray value. Each LED has its own PWM to control the lighting time. In this way, in a cycle of repeated lighting, each pixel only needs 4 pulses under 16-level grayscale, and only 8 pulses under 256-level grayscale, which greatly reduces the serial transmission frequency. With this method of decentralized control of LED grayscale, 256-level grayscale control can be easily realized.