There are two ways to control the LED display brightness.
Current through the LED display is a kind of change, general LED display tube allows continuous working current is controlled in 20 ma, in addition to the red LED display have saturation phenomenon, other LED display brightness basically proportional to the flow of electric current;
Another method is to use human eye visual inertia, using pulse width modulation method to realize gray scale control, which is periodic change light pulse width (
The duty ratio)
Cycle is short enough, as long as the repeated light (
The refresh rate is high enough)
, the human eye is feeling less than glowing pixels in jitter.
Due to pulse width modulation is more suitable for digital control, so in general microcomputer is used to provide the LED display shows the content of today, almost all of the LED display screen is adopts PWM to control the gray scale level.
LED display control system generally consists of main control box, scan and display control device is composed of three parts.
Main box from computer display card to get a screen pixel brightness of of all kinds of data, and then reassigned to a number of scanning board, scanning each one is responsible for the control of LED display screen lines,
While each line (
On the LED display screen display control signal is transmitted in serial mode.
There are two types of serial transmission display control signal way: one kind is centralized control each pixel gray scanning board, scanning board will come from the control box of the brightness values of all pixels decomposition (
The pulse width modulation)
And then all the opening of the LED display signal in pulse form (
Light is 1, not bright 0)
In line with serial transmission to the corresponding LED display screen, control whether the light.
This way using the device is less, but the serial transmission data volume is bigger, because in a repeated cycle of light, each pixel under the gray level 16 need 16 pulse, under the gray level 256 to 256 pulses, because the device operating frequency restricted, generally only to do gray level 16 LED display screen.
Another method is to scan the board serial transmission not every LED display the contents of the brightness of the switch signal instead of an 8 bit binary value.
Each LED display has a pulse width modulator to control the lighting time.
Thus, in a repetitive cycle of light, each pixel point under the gray level 16 only need four pulse, under the gray level 256 just eight pulse, greatly reduces the frequency of serial transmission.
With this kind of decentralized control full color LED display
method of gray level 256 gray scale control can be easily.
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