Leds is how to realize the display function

What is a LED?

In some semiconductor materials into the PN junction with the minority carriers will take extra compound majority carrier in the form of light energy of the energy released, which directly convert light energy. PN junction, minority carriers with reverse voltage to infuse, reason not to shine. This kind of use between electroluminescent principle called leds made diodes, appellative LED.

The LED emitting light colors and the luminous efficiency and production of material and process related LED, is now widely used there are red, green, blue 3 kinds. Because the LED lower voltages (1.5-3V), can active luminous and have certain brightness, brightness and can adjust voltage (or current), impact resistance, resistance and its vibration and long service life (100,000 hours), so in large display device, at present there is no other way showing the way and LED display dash.

The red and green LED put together as a pixel LCD display that made double color screen; or The red, green, blue three LED tube put together as a pixel display called three color screen or a full color. Make indoor the LED screen size of pixels was an average of two - 10 millimeter, often use put several can produce different gezer LED tube core encapsulation as a body, outdoor LED screen size of pixels for 12 - more than 26 mm, each pixel by several various monochromatic LED, common finished says pixel cone, double-color pixel canister generally by three red 2 green composition, three color pixel in 2 red cone of green 1. 1 Abram

No matter use leds make monochrome, double color or three color screen display image needs to each the LED constitutes a pixel luminous intensity must can adjust, the regulation of fine degree of gray level is the screen. Gray level higher, more exquisite displayed image, colour also abounded more, the corresponding display and control system is also more complicated. General 256 levels, color shade of images, and already very downy transition at level 16, color shade of color image is very obvious. The transition boundaries So, color LED the current were required to make the grade 256 gray.

Second, control the methods: LED luminance

There are two kinds of control method of LED brightness. One is to change the current flows through LED, general LED tube allows continuous working current in 20 ma or so, besides red leds have saturated phenomenon outside, other LED luminance basically flows through the current with proportional; Another method is to use the visual inert, eye with pulse width modulation method to achieve the gray control, also is cyclical change a light pulse width (namely 390v), as long as this repeat lit cycle short enough (namely refresh frequency is high enough), eye is feel glowing pixel in the wobbling. Due to the pulse width modulation is more suitable for digital control, so in widespread use of the microcomputer to provide LED display content today, almost all the LED screen are using pulse width modulation to control gray level.

The control system is usually LED master box, scanning plate and display control device three major components. Master box from the computer display adapters for a screen pixels in carded brightness data, then re-assigned to several pieces of scanning board, each scan responsible for controlling the LED screen on board several row (column), and each row (column) on the LED display control signal is transmitted by serial manner. There are two serial transmission display and control signals by means of: one kind is scanning board centralized control each pixel grayscale, scanning the board will come from control box in all pixel luminance values decomposition (namely pulse width modulation), then will all LED to the opening of pulse signal for 1, form (light bright 0) rows with serial mode to the corresponding LED, control its whether lighted. This way, using device serial transmission is less, but large quantities of data, because in a repeat lit cycle, each pixel in the 16th level gray need 16 pulse, under the 256 levels need below 256 pulse gray-scale devices working frequency, because restriction, general only makes the LED screen do 16 level gray.

Another method is the content of the serial transmission scanning board isn't each LED switch signals but an 8 bit binary brightness values. Each LED all have an own pulse width omdulatros to control the light of time. So, in a repeat lit cycle, each pixel grayscale only in the 16th grade four pulses, 256 need only 8 gray level under impulsive, and greatly reduce the serial transmission frequencies. Using this method of distributed control LED gray can be easily realized 256 level gray control.