Because of its simplicity, reliability, and flexibility, DMX512 quickly became the primary way to connect controllers (such as lighting consoles) to dimmers, fog machines, smart lights, and other special effects devices, has been developed to a way that the console with a standard digital interface control the dimmer .DMX512 surpasses the analog system, but it is not a complete replacement for the analog system.

        DMX512 USES eia-485 differential signaling on its physical layer, combined with a variable size, packet-based communication protocol.DMX512 does not include automatic error checking and correction, so it is not an appropriate control for dangerous applications, such as pyrotechnic or stage-controlled movements.The wrong trigger may be caused by electromagnetic interference, electrostatic discharge, improper cable termination, excessive cable length, or poor cable quality.

                     

         According to the standard definition and in order to distinguish the traditional auto 3-core cannon, the 5-core cannon is defined. However, in recent years, the 3-cor cannon is also increasingly used in DMX512 devices.The 5 pin line sequence is as follows:

                                                                                          

          Note: different from the traditional audio interface, Pin2 and Pin3 have opposite positive and negative values, and since Pin 4 and Pin 5 are spare links, that is currently undefined, they can only be connected to Pin1~3.

DMX512 special cable and maximum transmission distance

          DMX512 controller transmits differential serial data at 250kbit/s. In theory, the maximum length of a bus link can reach 1200 meters (3900FT), but this does not mean that the maximum length of a cable can be used is 1200 meters, Add a repeater and it goes up to 1200 meters ,the farther the transmission distance, the higher requirement for wire, can be on the premise of guarantee the characteristic impedance of 120 Ω bold cable.

          3 core cannon and 5 core interface can use 2 core with shielded twisted-pair cable, and cable must meet the characteristic impedance of 120 Ω, and characteristic impedance is the most important,  Mismatched characteristic impedance can distort digital signal waveform and increase error code.

          Many engineers use ordinary microphone cable or RVVP 2 x 0.752 link, and the two cables are low impedance, impedance is almost 50 ~ 70 Ω,  can not meet the standard demand120 Ω, makes greatly increase the reflex, shorten the transmission distance, especially after more than 50 meters, Error signals that are unpredictable and uncorrectable, irregular, completely or intermittently uncontrolled may occur, and even suddenly stop running.Use the mic line or RVVP line, even in the increase of conductor cross-sectional area can not increase the characteristic impedance, that is, even the thicker line can not extend the transmission distance, so be sure to use the professional DMX512 control line.

                     

           It needs to be reminded that the appearance and outside diameter of this wire are very close to the microphone cable. Be sure to look at the logo "DMX512" on the surface when using it on site, and do not use it wrongly.Be sure to pay attention to electrical indicators such as the characteristic impedance of the cable.The characteristic impedance is invisible to the untrained eye.

DMX512 Link and termination resistance

        DMX512 no more than 32 cell loads (single device connections) on a single bus network.If more than 32 cell loads need to communicate using the allocator, extend the parallel network.The load link USES RS485 chrysanthemum lotus, that is, all the loads are in series.

                      

           What need reminds is, the last set of load need to link a 120 Ω end resistance,End resistance can be used with 120 Ω impedance card head, also can use the small resistance element connected to the carnon of pin2 and pin3. Usually, there is no terminal resistance, and some systems can operate normally.However, there is no guarantee that the system will always operate normally without flickering, pausing, random or non-specified lighting effects.

Summary points:
1. Be sure to use a professional DMX512 control line
2. The load does not exceed 32 sets.
3. The final group be sure to use 120 ? end resistance load.