Full color LED display screens may sometimes experience garbled code due to signal issues. How to improve the reliability and stability of signal transmission is a very important issue. The signal weakens as the distance increases during transmission. Therefore, the selection of transmission media is particularly important.
The loss of signal is mainly due to the LC low-pass filter composed of distributed capacitance and distributed inductance of the cable. The higher the communication baud rate, the greater the signal attenuation.
Therefore, when the amount of data transmitted is not very large and the transmission rate requirement is not very high, we usually use a baud rate of 9600bps.
The following precautions should be taken when using RS-485 as a long-distance data transmission line:
1. Signal attenuation
No matter what medium is used for signal transmission, attenuation will occur during the transmission process. We can consider the RS-485 transmission cable as an equivalent circuit composed of several resistors, inductors, and capacitors.
The resistance of the wire has little effect on the signal and can be ignored. The distributed capacitance C of a cable is mainly generated by two parallel wires of a twisted pair.
The loss of signal is mainly due to the LC low-pass filter composed of distributed capacitance and distributed inductance of the cable. The higher the communication baud rate, the greater the signal attenuation.
Therefore, when the amount of data transmitted is not very large and the transmission rate requirement is not very high, we usually use a baud rate of 9600 bps.
2. Signal reflection in communication lines
In addition to signal attenuation, another factor that affects signal transmission is signal reflection. Impedance mismatch and impedance discontinuity are the two main reasons for signal reflection on the RS-485 bus.
① Impedance mismatch refers to the impedance mismatch between the 485 chip and the communication line. The reason for reflection is that when the communication line is idle, the entire communication line signal is disorderly. Once such reflected signals trigger the comparator at the input end of the 485 chip, an incorrect 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 pull them up and down respectively, so that unpredictable and chaotic signals will not appear.
② Impedance discontinuity, as the name suggests, is similar to the reflection caused by light entering one medium from another.
The above is a specific analysis of the reliability and stability of signal transmission on full color LED display screens, hoping to be helpful to you.
