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large giant LED screen brightness control method?
There are two ways to control the brightness of the LED. One is to change the current flowing through the LED. Generally, the LED tube allows the continuous working current to be around 20 mA. In addition to the saturation of the red LED, the brightness of the other LEDs is basically the same as the current flowing. Proportional; another method is to use the visual inertia of the human eye, using pulse width modulation to achieve gray control, that is, periodically changing the optical 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 does not feel that the illuminating pixels are shaking. Since pulse width modulation is more suitable for digital control, today, in general, the use of microcomputers to provide LED display content, almost all LED screens are Pulse width modulation is used to control the gray level.
LED control system usually consists of three main parts: main control box, scanning board and display control device. The main control box obtains the brightness data of each layer of pixels from the display card of the computer, and then re-allocates it to several scanning boards. The block scanning board is responsible for controlling several rows (columns) on the p6 outdoor LED screen, and the display control signals of the LEDs in each row (column) are transmitted in a serial manner. Currently there are two ways of serially transmitting display control signals: The gray level of each pixel is controlled centrally on the scanning board, and the scanning board decomposes the brightness values ​​of the pixels in each row from the control box (ie, pulse width modulation), and then turns on the ON signals of the LEDs of each row in a pulse form (lighting is 1 , does not light to 0) serially transmitted to the corresponding LED by line, control whether it is lit. This way uses less devices, but the amount of data transmitted serially is larger, because in a repeated lighting In the period, each pixel needs 16 pulses in 16 gray levels, and 256 pulses in 256 gray levels. Due to the limitation of the operating frequency of the device, the score LED screen can only achieve 16 gray levels.
 
Another method is that the serial transmission of the scan board is not the switching signal of each LED but an 8-bit binary brightness value. Each LED has its own pulse width modulator to control the lighting time. In a cycle of repeated lighting, each pixel requires only 4 pulses in 16 gray levels, and only 8 pulses in 256 gray levels, which greatly reduces the serial transmission frequency. The gray scale method can easily realize 256 gray scale control.
 
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