First, the classification of LED large screen signal transmission:
Wireless transmission: mainly rely on the frequency of wireless signal operation to classify, such as long wave, medium wave, short wave, microwave, etc.
The mobile phone signal is a wireless access method, and the mobile phone GSM operating frequency that is currently used in large quantities is 900 MHz, commonly known as 900 megabytes. There are many types of TV signals, such as cable TV: ordinary transmission of analog signals, digital television transmission of digital signals; television signals on satellites are digital signals.
Second, LED large screen 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 main causes of signal reflection on the RS-485 bus. Impedance mismatch, impedance mismatch is mainly the impedance mismatch between 485 chip and communication line. The reason for the reflection is that when the communication line is idle, the entire communication line signal is disordered. Once such a reflected signal triggers the comparator at the input of the 485 chip, an erroneous signal is generated. Our usual solution is to add a certain resistance to the A and B lines of the RS-485 bus, and then pull them up and down separately to avoid unpredictable clutter. The impedance is discontinuous and is similar to the reflection caused when light enters another medium from one medium. The signal suddenly encounters a small cable impedance at the end of the transmission line, and the signal will cause reflections in this place. The most common way to eliminate this reflection is to connect a terminating resistor of the same magnitude as the cable's characteristic impedance at the end of the cable.
Third, how to ensure the security performance of LED large-screen signal transmission process: We can develop a simple and reliable RS-485 communication protocol, when the communication distance is short, the application environment interference is small, one-way communication can realize the project function, but most applications The environment is not always such an ideal. Therefore, it is particularly important to develop a comprehensive communication protocol.
The specific method: the data is sub-packetized, and the data is packed by adding the frame header and the frame tail to each packet of data, wherein one byte is reserved as a check byte at the end of the frame. The lower computer compares the check byte calculated by itself with the check byte transmitted by the host computer, thereby issuing an instruction to the host computer, whether to resend the data of the packet or send the next packet of data. After the package is sent, send another packet until it is finished. Through such a verification retransmission mechanism, we can reduce the probability of error and make the communication system operate normally.
In summary, the signal weakens as the distance increases during transmission. Therefore, in order to ensure the playback effect of the LED display, reflecting the LED display relative to other advertising modes, the selection of the transmission medium of the LED display is particularly important.
