LED large screen signal transmission method
1. Classification of LED large screen signal transmission:
(1) Wireless transmission: It is mainly classified according to the different frequencies of wireless signals, such as long wave, medium wave, short wave, microwave, etc. Mobile phone signal is a kind of wireless access method, and the GSM working frequency of the mobile phone that is widely used now is 900MHz, commonly known as 900M. There are many types of TV signals, such as cable TV: ordinary ones transmit analog signals, while digital TV transmits digital signals; TV signals on satellites are all digital signals.
(2) Wired transmission: It can be divided into analog signal transmission, digital electrical signal transmission, and digital optical signal transmission.
2. LED large screen signal transmission project: In addition to signal attenuation, another factor affecting signal transmission is signal reflection. Impedance mismatch and impedance discontinuity are the two main 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, the signal of the entire communication line is disordered. Once such a reflection signal triggers the comparator at the input end of the 485 chip, an erroneous signal will be generated. Our 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 avoid unpredictable cluttered signals. Impedance discontinuity is similar to the reflection caused by light passing 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 reflections at this place. The most common method to eliminate this reflection is to connect a terminating resistor of the same size as the characteristic impedance of the cable across the end of the cable.
3. How to ensure the safety performance of the LED large screen signal transmission process: we can formulate a simple and reliable RS-485 communication protocol. When the communication distance is short and the application environment interference is small, one-way communication can realize the project function, but most applications The environment is not all this ideal. Therefore, it is particularly important to develop a complete set of communication protocols. The specific method is that the data is transmitted in packets, and the data is packaged by adding the frame header and the frame tail to the data of each packet, and one byte is left at the frame end 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 send an instruction to the upper computer, whether to resend the packet of data just now or to send the next packet of data, that’s it After one package is sent, the next package will be sent until it runs out. Through such a check retransmission mechanism, we can reduce the probability of errors and make the communication system operate normally.
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