LED has now penetrated into all walks of life. On the road, we can see the warm reminder signs on the LED display of the road. At the door of the store, we can see the advertising signs of the LED display used by the store. It can be said that the LED display has reached the limitless Therefore, it is essential for us to master some common sense of LED display. Let's follow our LED display manufacturer---Shenzhen YONGS Co., Ltd. to understand the control method of LED display brightness.
There are two ways to control LED brightness. One is to 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 brightness of other LEDs is basically proportional to the current flowing through; the other method is to use The visual inertia of the human eye, using the pulse width 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 The eye cannot perceive the shaking of the light-emitting pixels. Because pulse width modulation is more suitable for digital control, almost all LED 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. At present, there are two ways to serially transmit display control signals: one is to centrally control the grayscale of each pixel on the scanning board, and the scanning board decomposes the brightness value of each row of pixels from the control box (ie, pulse width modulation), Then, the turn-on signals of the LEDs in each row are transmitted to the corresponding LEDs in a serial manner by row in the form of pulses (1 when they are on, 0 when they are not on) to control whether they are lit. 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.
Another method is that what the scanner board serially transmits is not the switching signal of each LED but an 8-bit binary brightness 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.
The above is the control method of the brightness of the LED display screen. When we master it, we can control the brightness of the LED display screen well, so that it can maintain the brightness we need at any time.
