How to ensure that the LED display signal is stable and the reasons for garbled codes

The LED display screen in use suddenly appeared garbled due to signal problems. If it was at a major opening ceremony, the loss would be irreparable. Therefore, how to improve the reliability and stability of signal transmission has become an issue that engineers have to face. In the transmission process, the signal weakens as the distance increases. Therefore, the choice of transmission medium is particularly important. The following matters should be noted when using RS-485 as a long-distance data transmission line. 1. The attenuation of the LED display signal is not difficult to understand, no matter what kind of medium is used to transmit the signal, it will be attenuated during the transmission process. We can regard 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 the cable is mainly produced by two parallel wires of the twisted pair. The signal loss is mainly due to the LC low-pass filter composed of the distributed capacitance and distributed inductance of the cable. The higher the communication baud rate, the greater the signal attenuation. Therefore, when the amount of transmitted data is not very large and the transmission rate requirement is not very high, usually we use a baud rate of 9 600 bps. 2. Signal reflection in the communication line of the led display In addition to signal attenuation, another factor that affects signal transmission is signal reflection. Impedance mismatch and impedance discontinuity are the two main reasons that cause signal reflections on the RS-485 bus. 1. 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 messy. Once this kind of reflection signal triggers the comparator at the input of the 485 chip, an error signal will be generated. Our usual solution is to add bias resistors with a certain resistance to the A and B lines of the RS-485 bus, and pull them up and down respectively, so that there will be no unpredictable messy signals. 2. Impedance is discontinuous. As the name suggests, it is similar to the reflection caused by light entering another medium from one medium. The signal suddenly meets the cable impedance at the end of the transmission line with little or no cable impedance, and the signal will cause reflection at this place. The most common method to eliminate this kind of reflection is to bridge the end of the cable with a terminal resistor of the same size as the characteristic impedance of the cable to make the impedance of the cable continuous. Since the signal transmission on the cable is bidirectional, a terminal resistor of the same size should also be connected across the other end of the communication cable. 3. The influence of the distributed capacitance of the led display screen on the transmission performance of the RS-485 bus. The RS-485 transmission cable is usually a twisted pair, and capacitance is generated between the two parallel wires of the twisted pair. At the same time, a similarly small capacitance also exists between the cable and the ground. Since the signal transmitted on the RS-485 bus is composed of countless '1' and '0' bits, when encountering special bytes such as 0x01, the level '0' makes the distributed capacitors have sufficient time to charge. And when the level '1' suddenly comes, the charge accumulated by the capacitor cannot be discharged in a short time, which results in the deformation of the signal bit, which affects the quality of the entire data transmission. 4. The LED display screen develops a simple and reliable RS-485 communication protocol. When the communication distance is short and the application environment interference is small, we sometimes only need simple one-way communication to achieve all the functions of the project, but most of the application environment Not so ideal. Whether the integrated wiring in the early stage of the project is professional (such as keeping a certain distance between the signal line and the power line), the indecisability of the communication distance, the degree of interference around the communication line, whether the communication line uses twisted-pair shielded wire, etc., these factors are all for the system Normal communication has a great impact. Therefore, it is particularly important to develop a complete communication protocol. Using an LED display will inevitably encounter garbled characters, so how to troubleshoot the problem after the garbled characters appear on the LED display? 1. Software or control card problem. The garbled phenomenon may be that the LED display parameters are not set properly. At this time, you need to determine the scan configuration problem, usually 1/4 scan; if it is not a software problem, check whether there is a problem with the control card; if there is no problem after these tests If so, you can contact the service provider to solve it. 2. The problem of the cable. In the case of troubleshooting the power supply problem, test whether the power supply of the defective module is normal (if the abnormal first block is dark and bright 80% is a power supply problem). 3. Water leakage and water ingress. First of all, garbled characters are mostly related to the display of water leaks. Due to improper rain and waterproof measures, water is likely to enter after rain, causing short circuits on the circuit board, and garbled characters. If this happens, it is recommended to contact the supplier or repair factory immediately for repair. 4. Data transmission problem. The control circuit of the computer output to the LED display is faulty. Check the power supply and signal input part of the display. If the control system board is damaged, the data line interface is damaged, or the data line is damaged or connected reversely, it will cause the display screen garbled phenomenon. Garbled is a common problem of LED display. Don't worry about this type of problem. Carefully investigate the above possible causes. If the problem is not resolved, please contact the LED display manufacturer for after-sales service as soon as possible.