Καθώς η τεχνολογία των οθονών LED συνεχίζει να ωριμάζει, οι απαιτήσεις για μεγάλες οθόνες LED γίνονται όλο και μεγαλύτερες, από μονόχρωμες έως ολόχρωμες. Οι δύο μέθοδοι ελέγχου των δύο μεγάλων οθονών LED περιγράφονται παρακάτω:
One is to change the current flowing through the LED. The ordinary LED tube allows a continuous duty current of about 20 mA. Except for the saturation phenomenon of the red LED, the brightness of the other LEDs is basically proportional to the current flowing; however, although this adjustment method is Simple, but with the gradual improvement of LED large screen requirements, it is becoming more and more unsuitable for fast and accurate modulation. The following is a commonly used modulation method;
Another method is pulse width modulation (PWM), which uses the changing frequency that the human eye can feel, and uses the pulse width modulation method to achieve grayscale control, that is, periodically changing the light pulse width (ie 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 that the light-emitting pixels are shaking. Because pulse width modulation is more suitable for digital control, it has been widely used. A common method is to use a microcomputer to provide an LED display method. At present, almost all LED screens use pulse width modulation to control the gray level.
The LED control system generally consists of three parts: the main control box, the scanning board and the display control installation. The main control box obtains the brightness data of each color of the pixels of a screen from the computer display card, and then re{{0}}distributes it to several scanning boards, each scanning board is responsible for controlling several rows (columns) on the LED screen, and each The display control signal of the LED is 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 on the scanning board, and the scanning board will stop synthesizing the brightness values of each row of pixels from the control box (ie, pulse width modulation), Then, the conservative signals of each row of LEDs are transmitted to the corresponding LEDs in a serial manner in a pulsed manner (lighting is 1, no lighting is 0) to control whether they are lit or not. This method uses fewer devices, but the amount of data transmitted serially is large, 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 device task frequency, the LED screen can only achieve 16 grayscales.
Another way is that the scan board serially transmits 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 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 increases the serial transmission frequency. With this method of collectively controlling the LED grayscale, 256-level grayscale control can be easily achieved.
