LED Display
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Because the LED illumination color and the luminous efficiency with manufacture LED the material with the craft related, at present widely uses has red, green, the blue three kinds. Because LED working voltage low (only 1.5-3V), can shine on own initiative, and has certain brightness, brightness can use the voltage (or electric current) adjusts, itself bears the impact, the anti-vibration, the life long (100,000 hours), therefore in the large-scale graphic display device, still did not have other display mode and the LED display mode at present is a worthy opponent. Puts red and green LED in the same place takes a picture element manufacture the demonstration curtain to be called the bi-color screen or the colored screen; Red, green, the blue three kind of LED tube puts in the same place takes a picture element the demonstration curtain to be called the tricolor screen or the entire color screen. Manufactures the indoor LED screen's picture element size is 2-10 millimeters generally, uses frequently several kinds can produce the different primary color LED tube core to seal many a body, the outdoor LED screen's picture element size is 12-26 millimeters, each picture element is composed of certain each kind of single color LED, the common end product calls the picture element tube, the bi-color picture element tube by 3 red 2 is composed green generally, the tricolor picture element tube with 2 red 1 green 1 composes blue. Regardless of manufactures the single color, the bi-color or the tricolor screen with LED, wants the display image to need to constitute the picture element each LED illumination brightness to be able to adjust, its adjustment's fine degree demonstrates curtain's gray scale equivalent. The gray scale equivalent is higher, the demonstration image is more exquisite, the color is also richer, the corresponding display control system is also more complex. Generally 256 step gray scale image, color transition already very gentle, but 16 step gray scale's color image, the color transition demarcation line is very obvious. Therefore, the colored LED screen current requests to make above 256 step gray scales. Two kinds control the LED brightness the method. One kind is the change winds through LED the electric current, generally the LED tube permission continuous working electric current about 20 milliamperes, has the saturated phenomenon besides red LED, other LED brightness basically with the electric current which winds through becomes the proportion; Another method is uses the human eye the eye persistence, realizes the gray scale control with the pulse-duration modulation method, is also the periodic change light pulse width (i.e. dutyfactor), so long as this redundant lightens the cycle is short (i.e. refurbishing frequency to be high enough) enough, the human eye is cannot feel the illumination picture element in the vibration. Because the pulse-duration modulation suits in several controls, therefore is using the computer to provide LED demonstration content generally today, the nearly all LED screen uses the pulse-duration modulation to control the gray scale equivalent. The LED control system usually by the master control box, the scanning disc and obviously controls installs three major part is composed. The master control box gains a screen picture element assorted brightness material from computer's indicator, then redistributes for certain scanning discs, each scanning disc is responsible to control on LED screen's certain lines (row), but each line (row) on LED obviously controls the signal to use the way transmission in series. At present has two transmission display control signal way in series: One kind will be on the scanning disc a common control various picture elements gray scale, the scanning disc will come from control box's each line of picture element luminance value to carry on the decomposition (i.e. pulse-duration modulation), then (will lighten each line of LED clear signal take the pulse mode as 1, not bright will be 0) transmits on corresponding LED according to the line with the way in series, will control it whether to lighten. This way use component are few, but transmission's material quantity in series is big, because in cycle which, in repeatedly lightens, each picture element needs 16 pulses under 16 step gray scales, needs 256 pulses under 256 step gray scales, as a result of the component operating frequency limit, can only cause the LED screen generally to achieve 16 step gray scales. Another method is the scanning disc transmission content in series is not each LED switch signal, but is a 8 element binary place luminance value. Each LED has an own PDM keyer to control lightens the time. Thus, in the cycle which in repeatedly lightens, each picture element only needs 4 pulses under 16 step gray scales, under 256 step gray scales only needs 8 pulses, cut the transmission frequency greatly in series. Controls the LED gray scale with this kind of dispersion the method to be possible to realize 256 step gray scale control very conveniently.