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First of all DMX signal use differential-pair signal, RS-485. Many website said that each device have programble unique ID then we can send data to each ID by following protocol. (seem like they same way which Dynamixel motor used) But some device can connected by daisy-chain without configured ID for example, DMX LED strip which can connect and control in cascade maner also some DMX lamp don't have ID setting at all. This make me so confuse how the DMX work with daisy-chain in eletrical level.

I got more information from manufacturer. The LED chip is UCS512C4. and it got 4 pin when connected(the extra pin is labeled as ADDR). The controller is K-8000C which can write address to LED lamp some how. enter image description here

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DMX is simply many RS-485 receivers on a single bus. They all can receive every byte on the bus. Some luminaries can take multiple IDs, for example an RGB lamp could take three IDs starting from the ID set to the lamp.

DMX can be bidirectional if the controller and luminaries support it, so there can be some kind of autoconfiguration going on. The protocol is called RDM.

RGB LED strips are not DMX, each RGB LED removes bits meant for it and passes the rest of the bits on to the next RGB LED.

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  • \$\begingroup\$ RDM seem make sense. but I don't think it working on led strip doesn't it? \$\endgroup\$
    – M lab
    Commented May 8, 2021 at 18:20
  • \$\begingroup\$ If it's not a DMX light then it isn't. These daisy-chained LED strips use a protocol where one RGB led removes three bytes from the front and next bytes pass on on the next RGB pixel. \$\endgroup\$
    – Justme
    Commented May 8, 2021 at 18:30
  • \$\begingroup\$ I've added more information about led chip. \$\endgroup\$
    – M lab
    Commented May 13, 2021 at 11:57
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Question

How come DMX is so confusing? Is DMX for servo motors the same thing as DMX for RGB LED strips?

Answer

Yes, DMX is indeed confusing. First of all, there are very roughly two kinds of DMX's:

  1. Dynamixel's DMX or LewanSoul's serial bus servos use simplex UART or RS485 to daisy chained servos. Each servo can send and receive signals, so two wires are used for each daisy chain of servos.

  2. DMX WS2812B LED controllers, and only one send wire is need to communicate with all LEDs in each daisy chain. For WS2812B RGB LED strips, one wire is needed for each strip. So say, for three R, G, B strips, four wires: R, G, B, COM are required.

You might like to watch the video in Ref 1 to get a rough idea of the LED DMX controller and how to control the LEDs. For more details of the real DMX controllers, you can skim the 50+ pages of the catalog listed in the reference below.

References

(1) How to Control LED Tape With DMX - Worship Leader Hangout, 2018aug07 144,494 views

(2) LED DMX Controller Catalog (54 pages!) - AliEXpress

(3) DMX512 (Digital communication networks standard used to control stage lighting and effects) - Wikipedia

(3) K-8000C Manual

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    \$\begingroup\$ I've added more information about led chip. \$\endgroup\$
    – M lab
    Commented May 13, 2021 at 11:57
  • \$\begingroup\$ (1) I found the user guide and included the link in my reference list. (2) The user guide is very brief, so you need to set up the controller, connect the led strip and do trials and errors to figure out how to use it. \$\endgroup\$
    – tlfong01
    Commented May 13, 2021 at 14:32

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