LED display screen is widely used in civilization leisure square, prosperous trade base, commercial street, railway stations, subway, shopping malls and other places.
Because of its use in the field of diversity, complexity, the audio and video signal transmission is stable, reliable, fluency is also put forward higher requirements.
Single played or network broadcast LED display signal using the transmission way of diversification.
Common LED display signal into the wired signal transmission cable, GPRS, 3 g and 4 g wireless signal.
A, 1, the classification of the LED display signal transmission wireless transmission: first rely on wireless signal to the frequency of different, such as long wave, medium wave, short wave, microwave, etc.
Cell phone signal is a kind of wireless access method, a lot of use of mobile phones in 900 MHZ GSM operation frequency.
Television signals varieties more, such as cable television: general transmission of analog signals, digital television is the transmission of digital signal;
Satellite TV signals are digital LED display.
2, cable transmission, and can be divided into analog signals, digital signals transmission, digital optical signal transmission.
Second, large LED display signal transmission project in addition to the signal attenuation, affect another element of the signal transmission is that the signal reflection.
Impedance mismatches and impedance does not have to be RS -
A 485 bus signal reflection of two primary reasons.
Impedance mismatch, the impedance mismatch between primary is 485 chip and communications lines of impedance mismatch.
Lead to reflection because in communications lines free, all communications lines signal at sixes and sevens, once such reflection signal triggered the 485 chip contrast at the input device, signal fault occurs.
The usual solution is to RS -
485 bus line A and B plus must value bias resistors, then up and down, separation can not prevent the unpredictable clutter signal.
Impedance is not string, is with the light from one medium into another medium as a result of reflection is similar.
Signal in the cable impedance is very small, but at the end of a transmission line and signal in the local will lead to reflection.
To eliminate the reflection of the most commonly used method, is at the end of the cable a jumper and the characteristic impedance of the cable termination resistors of the same range.
Three, how to guarantee the safety of LED display signal transmission process function we can draw up a brief RS - secure
485 communication protocol, when the communication interval shorter, using environmental trouble hour, one-way communication function will be able to complete the project, but most of the use of the environment are not all so this ideal.
So, to formulate a set of perfect communication protocol is particularly important.
Specific measures, to transmit data of the subcontract, after every packet data, plus the frame head and tail frame to the data package, meantime tail frame for a byte as a checking byte.
Under a machine after their accounting check byte as compared with PC transmit to check byte, announced to the upper machine instructions, is from the beginning to send just a packet of data under the data packet is then distributed, so under a pack of a pack after again, until the stop.
After such a check retransmission mechanism, we can reduce the probability of error, make communication system normal operation.
In short, in the process of transmission signal, with the increase of interval.
So, in order to assure the playback effect of LED display, LED display performance relative to other advertising communication way, LED display of the transmission medium selection is particularly important.