There are two ways to control the LED brightness.
Current through the LED is a kind of change, general LED tube allows continuous working current is controlled in 20 ma, besides red leds have saturation phenomenon, other LED 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 the pulse width modulation is more suitable for digital control, so widely used in microcomputer to provide LED display content today, almost all the LED screen is controlled by pulse width modulation to grayscale.
LED control system usually consists of main control box, scanning board 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 control of the LED screen lines (
While each line (
On the LED 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 LED to the opening of the signal pulse form (
Light is 1, not bright 0)
In line with serial transmission to the corresponding LED on, 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, normally only the LED screen be gray level 16.
Another method is to scan the board serial transmission content not every LED the brightness of the switch signal instead of an 8 bit binary value.
Each LED has an own pulse width modulator to control the light 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 LED gray-scale method can easily achieve a level 256 gray scale control.