LINETX Technology's DMX RDM light control system is mainly composed of DMX main control equipment, DMX decoding driving equipment, bus and amplification equipment, power supply equipment, etc. The DMX main controller sends DMX light effect data and manages the DMX equipment through the RDM protocol; the DMX decoder receives the DMX data sent by the main controller and decodes and drives the corresponding lighting fixture. The connection diagram of the system is as follows:
Because the DMX bus is a shared bus, there is a limitation on the ability to mount the bus. When there are too many devices mounted on the DMX bus, or when the DMX bus transmission distance is too long, the DMX signal will be significantly attenuated and the AB line signal amplitude If it is lowered, it will cause DMX communication failure after exceeding a certain threshold.
So under what circumstances do you need to use a bus amplifier to amplify the bus signal before transmitting it? Because the driving ability of the main control equipment is different, or the bus length and the material of the bus wire used during construction are different, there is no requirement for a fixed number of devices to add a bus amplifier. According to experience, LINETX Technology DMX main controller is used. In the case of a shielded twisted-pair DMX bus with a diameter of 1.0, the maximum number of DMX decoding devices to be mounted is 256. It is recommended that 100 meters / 128 devices be added with a DMX bus amplifier.
It should also be noted that LINETX decoding DMX equipment supports RDM commands, so if RDM needs to be supported, the DMX amplifier needs to support bidirectional transmission function, otherwise the RDM function of DMX will be limited.
What is an isolated DMX bus interface? The isolated DMX bus physically isolates the entire DMX bus from the local system through optical or magnetic coupling technology and isolated power technology. Isolated DMX interface will effectively isolate the interference signal on the bus, and although the cost of the isolated DMX interface is higher than that of the non-isolated DMX interface, the isolated DMX bus will effectively prevent the The high voltage on the bus is connected to the equipment side, posing a threat to equipment and personal safety.
Another important role of the isolated DMX interface is that because the reference potential of the isolated interface is what we call "floating", this avoids different common-mode voltage differences between the access points to ground, which can cause interference with DMX communications, even due to The common-mode potential difference to ground is too large and the equipment is burned.
All in all, the isolated DMX interface is more secure, has better anti-interference performance, and the cost is higher. Whether to use the isolated DMX interface depends on the actual situation of the project.
The so-called DMX bus terminal resistance is a matching method to reduce the reflected wave of the signal according to the transmission line theory. When high-frequency signals are transmitted, the signal wavelength is shorter than the transmission line, and the signal will form reflected waves at the end of the transmission line, which will interfere with the signal. For stable transmission, add a terminating resistor at the end of the transmission line to avoid signal reflection and echo.
In fact, in most cases, it is not necessary to add a terminating resistor. Because the transmission speed of DMX is 250kbps, when the transmission distance is less than about 300 meters, not adding a terminating resistor will not significantly affect the signal transmission. Need to add a termination resistor of about 120 ohms.
Yes, LINETX's multi-point drive equipment can be centrally installed in the cabinet for easy management and maintenance, as shown below: