With the LED display technology continues to mature, led large screen requirements are getting higher and higher, from monochrome to full color. Here are two kinds of LED large screen of the two control methods:
One is to change the current flowing through the LED, ordinary LED tube to allow continuous task current in 20 mA or so, in addition to red LED saturation phenomenon, the rest of the LED brightness is basically proportional to the flow of current; but this adjustment method Simple, but with the LED large screen requirements gradually improve, but also more and more suited to fast and accurate modulation, the following accepted a commonly used modulation method;
Another method is the pulse width modulation (PWM), the use of the human eye can feel the frequency of change, with the pulse width modulation method to achieve gray-scale control, that is, periodically change the optical pulse width (ie, duty cycle) Just this repeated light cycle is short enough (ie, the refresh frequency is high enough), the human eye is not feeling the luminous pixels in the trembling. As the pulse width modulation is more suitable for digital control, so get a lot of use. The common way is to use the computer to provide LED display. Almost all of the current LED screen is the use of pulse width modulation to control the gray level.
LED control system generally by the main control box, scanning board and display control installation of three major components. The main control box from the computer graphics card to obtain a screen pixel color brightness data, and then re-deployed to a number of scanning plates, each scanning board as a control LED screen on a number of rows (columns), and each row (column) LED display and control signals are transmitted in a serial manner. There are two kinds of serial transmission display control signal way: one is to scan the board to control the gray point of each pixel, the scan board from the control box of the pixels of the line to stop the brightness of the synthesis (ie, pulse width modulation) And then the line of the old LED signal to pulse mode (lighted to 1, not bright 0) by line serial transmission to the corresponding LED, to control whether it can light up. This method uses fewer devices, but the amount of serial transmission of data is large, because in a repeated light cycle, each pixel in 16 grayscale requires 16 pulses, 256 levels of gray demand 256 pulses, due to device task frequency restrictions, the general can only make LED screen 16 gray scale.
Another way is to scan the board in a serial transmission mode instead of each LED's switching signal but an 8-bit binary luminance value. Each LED has its own pulse width modulator to control the lighting time. In this way, in a repeated light cycle, each pixel in the 16-level gray-scale request only 4 pulses, 256 gray-scale only 8 pulses, greatly increased the serial transmission frequency. With this aggregation control LED gray scale method can be very convenient to achieve 256 levels of gray control.