LED displays are widely used in leisure and civilized squares, bustling commercial 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 fluency of audio and video signal transmission. The signal transmission method adopted by the LED display screen for single-screen broadcast or network simultaneous broadcast is diversified. Common LED display signals are divided into wired signals transmitted by network cables, and wireless signals such as GPRS, 3G, and 4G.
1. Classification of LED display signal transmission
1. Wireless transmission: mainly rely on different frequencies of wireless signal operations for classification, 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 nowadays is 900MHz. There are many types of TV signals, such as cable TV: generally it transmits analog signals, while digital TV transmits digital signals; the TV signals on satellites are all digital LED display signals.
2. Wired transmission: It can be 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 reasons that cause the RS-485 bus to constitute signal reflection. Impedance mismatch, the primary impedance mismatch is 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 this kind of reflection signal triggers the comparator at the input of the 485 chip, an error signal will occur.
The usual solution is to add bias resistors of a certain resistance to the A and B lines of the RS-485 bus, and then pull them high and low separately, which can prevent unpredictable messy signals. Impedance is not connected, which is similar to the reflection caused when light enters another medium from one medium. The signal suddenly encounters a very small cable impedance at the end of the transmission line, and the signal will cause reflection in this place. The most common way to eliminate this kind of reflection is to bridge the end of the cable with a terminal resistor of the same size as the characteristic impedance of the cable.
Third, how to ensure the safety function of the LED display signal transmission process
We can draw up a simple and reliable RS-485 communication protocol. When the communication interval is short and the use environment is less disturbed, the one-way communication can complete the project function, but most use environments are not so ideal. Therefore, it is particularly important to draw up a complete communication protocol. The specific method is to transmit the data in packets, and pack the data by adding the header and end of each packet of data, during which one byte is left 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 from the upper computer, and then announces the command to the upper computer, whether it is to send the data just now from the beginning or to send the next packet of data. In this way, one package will be sent and then the next package will be sent until it stops. Through such a verification and retransmission mechanism, we can reduce the probability of errors and make the communication system work normally.
In short, the signal in the transmission process, with the increase of the interval and weaken. Therefore, in order to ensure the playback effect of the LED display screen, the selection of the transmission medium of the LED display screen is particularly important for the performance of the LED display screen compared to other advertising communication methods.
