The LED lighting panel reports: LED is a light emitting diode, the English abbreviation for light emitting diode, abbreviated as LED. It is a display method that controls semiconductor light emitting diodes. Its approximate appearance is that many are usually It is composed of red light-emitting diodes and displays characters by turning the lights on and off. A display screen used to display various information such as text, graphics, images, animations, quotes, videos, and video signals.
As the technology of LED displays continues to mature, the requirements for large LED screens are also increasing, from monochrome to full color. The following introduces two control methods for two large LED screens:
One is to change the current flowing through the LED. Ordinary LED tubes allow the continuous task current to be around 20 mA. Except for the saturation phenomenon of the red LED, the brightness of the remaining LEDs is basically proportional to the current flowing; however, this adjustment method Simple, but with the gradual improvement of the requirements of large LED screens, it is also less and less suitable for rapid and accurate modulation. The following accepts a commonly used modulation method;
Another method is Pulse Width Modulation (PWM), which uses the changing frequency that the human eye can perceive and uses pulse width modulation to achieve grayscale control, that is, periodically changing the optical pulse width (that is, the duty cycle), As long as the period of repeated lighting is short enough (that is, the refresh frequency is high enough), the human eye cannot feel the luminous pixels shaking. Because pulse width modulation is more suitable for digital control, it has been widely used. The common method is to adopt a microcomputer to provide LED display. At present, almost all LED screens adopt pulse width modulation to control the gray level.
The control system of LED is generally composed of three parts: main control box, scanning board and display control installation. The main control box obtains the brightness data of each color of one screen pixel from the computer display card, and then re-allocates it to several scanning boards, each scanning board is used to control several rows (columns) on the LED screen, and each row (column) The display and control signals of the LED are transmitted in a serial manner. At present, there are two ways of serially transmitting display control signals: one is to collectively control the grayscale of each pixel point on the scanning board, and the brightness values ​​of each row of pixels from the control box on the scanning board are not synthesized (that is, pulse width modulation), Then, the old signals of the LEDs in each row are transmitted to the corresponding LEDs in a pulse manner (lighting is 1 and not lighting is 0) in a serial manner according to the row to control whether it can be lit. This method uses fewer devices, but the amount of serial transmission data is larger, because in a repeated lighting cycle, each pixel requires 16 pulses at 16 gray levels and 256 gray levels 256 pulses, due to the limitation of the task frequency of the device, can usually only make the LED screen achieve 16 levels of gray.
Another way is to scan the board serial transmission method is not the switch 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 this way, in a cycle of repeated lighting, each pixel point requests only 4 pulses in 16-level grayscale, and only 8 pulses in 256-level grayscale, greatly increasing the serial transmission frequency. Using this method of aggregate control of LED grayscale can easily achieve 256-level grayscale control.
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