Current through the LED is a kind of change, general LED tube core 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; Also can make use of the human eye visual inertia, using pulse width modulation method to realize gray scale control, which is periodic change light pulse width, as long as the repetition of the light cycle is short enough, the human eye is feeling less than glowing pixels in jitter. Since pulse width modulation is more suitable for digital control, it is generally used for the display content of LED display by microcomputer. Almost all the LED screens are equipped with pulse width modulation to control gray level.
The other is that the content of the scan board serial transmission is not the switching signal of each LED but an 8-bit binary brightness value. Each LED has its own pulse width modulator to control the lighting time. In this way, in a cycle of repeated lighting, each pixel requires only four pulses at the level of 16 gray degrees, and only eight pulses are needed at the 256 level grayscale, greatly reducing the serial transmission frequency. The method of dispersing LED grayscale with this kind of dispersion can easily realize the 256 level grayscale control.