A classification of LED large screen signal transmission
1, wireless transmission, by using the wireless signal to the frequency of different categories, such as long wave, medium wave, short wave, microwave, etc. Cell phone signal is a kind of wireless access mode, now a lot of use of mobile GSM frequency work at 900 MHZ, commonly known as 900 million. TV signals is much more different species, such as cable TV: ordinary transmission of analog signals, digital television is the transmission of digital signal; Satellite TV signals are digital signals.
2, cable transmission, and can be divided into analog signals, digital signals transmission, digital optical signal transmission.
B, LED large screen signal transmission project: in addition to the signal attenuation, is another contributing factor to affect the signal transmission of signal reflection. Impedance mismatches and impedance discontinuity leads to the formation of a RS - 485 bus signal is the reflection of the two main reasons. Impedance mismatch, impedance mismatch is mainly 485 chip and the impedance mismatch between communications lines. Cause reflection because in communications lines free, the communication signal is desultorily, once such reflection signal triggered the 485 chips at the input comparator, can produce the wrong signal.Our usual solution is to RS - 485 bus line A and B with A certain value of bias resistors, then up and down, respectively, this can avoid unpredictable clutter signal. Impedance discontinuity, is with the light from one medium into another medium caused by reflection is similar. Signal cable impedance is very small, in the end of the line suddenly signal will cause reflection in a place like this. To eliminate this kind of reflection of the most commonly used method, it is a jumper at the end of the cable and the characteristic impedance of the cable termination resistors of the same size.
C, how to ensure the safety performance of outdoor led display signal transmission process: we can develop a simple and reliable RS - 485 communication protocol, when the communication distance is shorter, hours application environment interference, one-way communication can achieve project function, but most applications are not all like this ideal. So, formulate a set of perfect communication protocol is particularly important. Specific methods, to transmit data of the subcontract, through every packet data combined with data in the frame head and tail frame of packaging, which frame tail leave a byte as a checking byte.Under a machine check byte and calculated by the own PC transmit to check byte, issue instructions to the upper machine, whether to send just the packet data is then issued under a packet of data, like a pack of hair under the recurrence of until after. Through such a check retransmission mechanism, we can reduce the error probability, make communication system normal operation.
In short, the signal in the process of transmission, decreases with the increase of distance. So, in order to make sure that the outdoor led display effect, reflect the LED display screen relative to the other way of advertising communication, outdoor led display, it is particularly important to the selection of transmission medium.
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