LED display transmission signal parse
LED displays are widely used in leisure and civilization squares, prosperous business bases, commercial streets, railway stations, subways, shopping malls and other places. Because of the diversity and complexity of its application fields, higher requirements are also put forward for the stability, reliability and smoothness of audio and video signal transmission. The signal transmission methods of single-screen playback or network simulcasting LED display are diversified. Common LED display signals are divided into wired signals transmitted by network cables, GPRS, 3G, 4G and other wireless signals.
1. Classification of LED display signal transmission
(1) Wireless transmission: It is mainly classified according to the different frequencies of wireless signal operations, such as long wave, medium wave, short wave, microwave, etc. The mobile phone signal is a wireless access method, and the GSM operating frequency of many mobile phones used today is 900MHz. There are many types of TV signals, such as cable TV: generally, it transmits analog signals, and digital TV transmits digital signals; the TV signals on satellites are all digital signals of LED display signals.
(2) Wired transmission: It can be further divided into analog signal transmission, digital electrical signal transmission, and digital optical signal transmission.
2. LED display large signal transmission project
In addition to signal attenuation, another factor that affects signal transmission is signal reflection. Impedance mismatch and impedance discontinuity are the two primary causes of signal reflections on the RS-485 bus. Impedance mismatch, impedance mismatch is mainly the impedance mismatch between the 485 chip and the communication line. The reason for the reflection is that when the communication line is idle, all the communication line signals are messed up. Once such a reflection signal triggers the comparator at the input of the 485 chip, a faulty signal will occur.
The usual solution is to add a bias resistor with a certain resistance value to the A and B lines of the RS-485 bus, and then pull up and down respectively, which can prevent unpredictable messy signals. Impedance is not connected and is similar to the reflection caused when light passes from one medium into another. The signal suddenly encounters a small impedance of the cable at the end of the transmission line, and the signal will cause reflection in this place. The most common way to eliminate this reflection is to connect a terminating resistor with the same size as the characteristic impedance of the cable at the end of the cable.
3. How to ensure the safety function of the LED display signal transmission process
We can formulate a simple and reliable RS-485 communication protocol. When the communication interval is short and the use environment is less disturbed, one-way communication can complete the project function, but most use environments are not so ideal. Therefore, it is particularly important to formulate a complete set of communication protocols. The specific method is to transmit the data in packets, and package the data by adding the frame header and the frame tail to the data of each packet, and leave a byte at the end of the frame as a check byte. The lower computer compares the check byte calculated by itself with the check byte transmitted by the upper computer, so as to announce the command to the upper computer, whether to send the previous packet of data from the beginning or to send the next packet of data. In this way, after one package is sent, the next package will be sent until it is finished. Through such a verification and retransmission mechanism, we can reduce the probability of errors and make the communication system operate normally.
In short, in the process of transmission, the signal weakens as the interval increases. Therefore, in order to ensure the playback effect of the LED display, the selection of the transmission medium of the LED display is particularly important.