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May 27,2021| LED Knowledge
LED Gray can also be called LED brightness. Gray scale is also called midtone (Half-tone) , Mainly used to transfer pictures, respectively 16 level, 32 level, 64 Level three methods, it uses matrix processing to process the pixels of the file into 16 , 32 , 64 Hierarchical levels to make the transmitted pictures clearer. Whether it’s a monochrome, two-color, or three-color screen, to display images or animations, you need to LED The luminous gray scale is adjusted, and the fineness of the adjustment is what we usually call the gray scale.
There are two kinds of controls LED Gray scale method: one is to change the current flowing, the other is pulse width modulation. 1. Change flow LED 的current. general LED The tube allows continuous working current in 20 About milliampere, except for red LED In addition to saturation, other LED The gray scale is basically proportional to the current flowing ; Another method is to use the visual inertia of the human eye and use pulse width modulation to achieve grayscale control, that is, to periodically change the light pulse width ( Duty cycle ) , As long as the period of repeated lighting is short enough ( That is, the refresh rate is high enough ) , The human eye can't feel the luminous pixels shaking.
Because pulse width modulation is more suitable for digital control, it is generally used to provide LED Show content today, almost all LED The screen adopts pulse width modulation to control the gray level. LED The control system is usually composed 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 screen pixel from the computer's display card, and then redistributes it to several scanning boards, each of which is responsible for control LED Several lines on the screen ( Column ) , And each line ( Column ) on LED The display control signal is transmitted serially.
There are currently two ways to serially transmit display control signals:
1. One is to centrally control the gray scale of each pixel on the scanning board, and the scanning board decomposes the gray value of each row of pixels from the control box. ( Pulse width modulation ) , And then add each line LED The turn-on signal is in pulse form ( Light up as 1 , Does not light up as 0) Serially transmitted to the corresponding line by line LED To control whether it is lit. This method uses fewer devices, but the amount of serially transmitted data is larger, because in a repeated lighting cycle, each pixel is 16 Needed in grayscale 16 Pulses in 256 Needed in grayscale 256 Pulses, due to the device’s operating frequency limitation, generally only LED Screen to do 16 Grayscale.
2. One is pulse width modulation. The content of the serial transmission of the scan board is not every LED Switch signal but a 8 Bit binary gray value. Each LED Each has its own pulse width modulator to control the lighting time. In this way, in a repeated lighting cycle, each pixel is 16 Only need 4 Pulses, 256 Only need 8 This pulse greatly reduces the frequency of serial transmission. Decentralized control LED The gray-scale method can be easily implemented 256 Grayscale control.