LED grayscale can also be called LED brightness. Grayscale is also called Half-tone, which is mainly used to transmit pictures. There are three ways of 16, 32, and 64 respectively. It uses matrix processing to process the pixels of the file into 16, 32, and 64. layer to make the transmitted picture clearer. Whether it is a single-color, two-color, or three-color screen, 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 gray level 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, LED tubes allow a continuous working current of about 20 mA. Except for the saturation phenomenon of red LEDs, the gray scale of other LEDs is basically proportional to the current flowing; another method is to use the visual inertia of the human eye to use pulse width The modulation method is used to achieve gray scale control, that is, to periodically change the light pulse width (that is, the duty cycle). As long as the cycle of repeated lighting is short enough (that is, the refresh frequency is high enough), the human eye will not feel that the light-emitting pixels are on. shake. Because pulse width modulation is more suitable for digital control, today when microcomputers are commonly used to provide LED planar interactive display content, almost all LED screens use pulse width modulation to control gray levels. The LED control system usually consists of three parts: the main control box, the scanning board and the display and 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 them to several scanning boards. Each scanning board is responsible for controlling several rows (columns) on the LED screen, and each row (column) The display and control signal of the upper LED is transmitted in a serial manner.
There are currently two ways to transmit display control signals serially:
1. One is to centrally control the gray level of each pixel on the scanning board. The scanning board decomposes the gray value of each row of pixels from the control box (that is, pulse width modulation), and then transmits the turn-on signal of each row of LEDs in the form of pulses. (Lighting is 1, non-lighting is 0) It is transmitted to the corresponding LED in serial mode by row to control whether it is on 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 at 16 gray levels, and 256 gray levels. 256 pulses, due to the limitation of the operating frequency of the device, generally can only make the LED screen achieve 16 gray levels.
2. One is pulse width modulation. The content transmitted serially by the scanning board is not the switch signal of each LED but an 8-bit binary gray value. Each LED has its own PWM to control when it is lit. In this way, in a cycle of repeated lighting, each pixel only needs 4 pulses at 16 gray levels, and only 8 pulses at 256 gray levels, which greatly reduces the serial transmission frequency. With this method of decentralized control of LED gray scale, 256-level gray scale control can be easily realized.
