Lighting control by DMX standard
DMX-512 is based on the English name Digital Multiplexing (simply simplified multi-channel digital signal transmission over one line). It was developed by the USITT (United States Institute for Theater Technology) in 1986 and modified in 1990 (DMX512 / 1990). In 1998, USITT began efforts to modify and subsequently create an ANSI standard called “E1.11, USITT DMX512-A” or DMX512-A for short.
It was developed primarily to unify the ways of controlling light sources (dimmers). It allows us to communicate / control 512 dimmers interconnected in one loop. Over time, it began to be used not only to control dimmers, but also various devices on the scene, such as fog machines, rotating lights, etc.
The DMX-512 uses as a transmission medium a metal conductor with at least three cores going from the DMX signal source to / through its destination. The network is of the BUS type with a length of up to 1200 m with a maximum of 32 devices in one BUS (bus). The buses can be expanded using the so-called DMX splitters. STP (shielded twisted pair) with an impedance of 120 ohms is used as the metallic line. The signal carrier is 0-10VDC. The signal is unidirectional, so it has one source that sends the signal to the whole loop without feedback. There is a lack of control and correction of possible transmission errors. For this reason, the DMX standard is not recommended for use in “sensitive” applications, such as control of pyrotechnics, laser displays and the like.
The basic DMX signal is an asynchronous 250kbaud serial, 8 data bits with one start bit and two stop bits (without parity). With the start mark of the packet frame based on the RS-485 standard. The framework consists of 513 bits.
The DMX-512/1990 specifies both a standard XLR-5 type connector and a female output (OUT) and a male input (IN) signal. In the DMX512-A standard (E1.11-2008), this recommendation was supplemented by 8-pin RJ-45 connectors to protect the space required for XLR connectors. When manufacturers use XLR-3 type connectors (not standard) for DMX devices, ie the 3-pin version, which is also used for audio devices. In this case, care must be taken to ensure that the DMX signal does not enter the inputs of the audio equipment. The DMX signal usually has a higher voltage than the audio signal, so it can damage these devices.