What Are DMX Splitters?

DMX512 protocol is a data dimming protocol proposed by the United States Stage Lighting Association (USITT), which gives a protocol standard for communication between lighting controllers and lighting equipment. Since it was proposed in 1990, the full name of the protocol It is USITTDMX512 (1990). The proposed protocol provides a good standard for controlling lighting equipment using digital signals. ^[1]

DMX512 is a digital dimming protocol. It can be used to digitally control dimmers and other control equipment in stages, theaters, studios and other places. It is suitable for more and more master-slave control systems. With the multi-point bus structure, there is no blockage of the information path, and the connection is simple and the reliability is high.

Although the lighting control system has been developed into a networked control system, the DMX512 signal system is still the most widely used system. Even for a large networked light control system, the control end still uses a large number of DMX512 signal control methods.

The DMX512 protocol is applicable to a point-to-multipoint master-slave control network system. According to the requirements of DMX512 data transmission rate and the characteristics of decentralized control network, the design of the physical layer uses RS-485 bus transceivers, and the bus uses a pair of twisted pairs to connect the dimmer and the dimmer.

With the application and popularization of digital technology and computer technology, computer dimmers have appeared, and D54, AVAB, CMX, PMX, EMX and other analog and digital communication protocols have appeared. Since the above protocol standards are the respective protocol standards of each manufacturer, their compatibility is not good, and there is a problem with the mutual use of equipment. Later, in order to solve the problem of equipment commonality of various manufacturers, the United States Institute for Theatre Technology (USITT) formulated the DMX512 protocol in the early 1980s. The DMX512 protocol is a Digital Multiplex (DMX) protocol. After the agreement was made, after modification, USITT standardized the DMX512 protocol in 1990 and formed DMX512-1990. At present, almost all manufacturers of lighting and stage equipment support this control protocol. As a widely used digital lighting data protocol, DMX512-1990 has also become an international standard for lighting control.

The unification of the DMX512 protocol enables equipment from various manufacturers to be connected to each other, which greatly improves compatibility. At the same time, because the DMX512 protocol uses a serial method to transmit digital signals, only one signal line is required between the console and the device, which greatly simplifies the connection line between the console and the device ^[2]

The DMX512 protocol has certain requirements for the data transmission rate. The typical transmission rate is 250kbps. The duration of each corresponding bit is 4us, and the duration of each data frame is 44us. The protocol also specifies each DMX512 data packet. Supports up to 512 frames of data at a time. The format of the DMX512 packet is shown in Figure 1 below.

Compared with other protocols, the DMX512 protocol has the following characteristics:

(1) The signal is transmitted based on the differential voltage.

There are several issues that need attention when using DMX512 signals.

It is very useful to carry a portable DMX512 signal tester at any time. It can check errors in the system at any time, quickly find problem areas, and troubleshoot in time to ensure the normal operation of the lighting control system.

The use of qualified signal lines can greatly reduce the troubles in the work. According to the requirements of the DMX512 protocol standard, the twisted-pair shielded wires that meet the specifications are used to make the signal lines. Audio cables must not be used instead. The correct connection of the cylindrical plug core wire also needs attention. In actual work, many failures are caused by problems such as broken signal lines, desoldering of signal line connectors, and incorrect connection of wire numbers. Therefore, check the continuity of the signal line and the phase of the core wire before use. , Can achieve the effect of doing more with less.

When using a three-core DMX512 cylindrical plug, especially when using a five-to-three or three-to-five signal adapter, be sure to pay special attention to the equipment s technical requirements for signal phase and correct the wrong signal connection in time. line.

Check the ground connection of the controlled device and the DMX512 cylindrical plug. According to the DMX512 standard, both the 1st core of the cylindrical plug and the 1st line of the controlled device are not allowed to be connected to the shell. Only the 1st DMX512 output port of the console is allowed. The wire is connected to its chassis. Therefore, after connecting the signal line of the control system, use a tester or a multimeter to check whether there is a shell connection problem on the 1st line. Once it is found, it should be eliminated immediately. Otherwise, the signal system may be damaged due to the accidental electrification of the equipment case.

When controlling different types of scanners on the same console, the equipment of each manufacturer will be different, and it is easy to cause problems when mixed. Therefore, it is best to install isolation amplifiers between them to separate different types of scanners. Computer lights are used in isolation. In addition, it is also important to install isolation amplifiers between equipment from different companies when renting scanners or other equipment from other companies.

Pay attention to separate the power supply of the computer light from the power supply of other electrical equipment (such as silicon boxes and high-power lamps) in the studio or the performance venue, otherwise it is very easy to cause the computer to be overloaded by other electrical equipment. Damage to the lamp.

Remember to add a 120 terminal resistor at the end of the signal connection line. According to the requirements of the DMX512 signal protocol, the terminal resistor must be connected at the end of each string of signal chain to form a "closed loop" of the control loop. Therefore, in practice In work, prepare a few more terminating resistors.

Pay attention to the unit load of DMX512 system, so that the unit load of each output port cannot exceed 32, and if necessary, add a signal distributor. In addition, according to our experience, the length of the signal line from the console or distributor to the end-controlled equipment must be less than 200m to have a good control effect.

Pay attention to the correct setting of the address code, especially when using scanners, you must be clear about the number of channels and the setting method of the address code. Some scanners (such as HIGHEND in the United States and SGM in Italy) have their special features. Special attention should be paid to the setting method of the address code.

When laying DMX512 signal cables, try to avoid laying them close to the power cables and light cables in parallel and as close as possible to reduce the interference of the power supply and dimming silicon box on the control signals ^[3] .