DMX Terminations

DMX512 employs RS-485 differential signaling at its physical layer.  DMX512 uses a unidirectional simplex communication protocol.

the following is a paraphase from Wiki:  DMX512 is a bus network that works upto 1,200 metres long, provided you don’t have  more than 32 receivers on a single bus. If more than 32 recivers are needed in a single universe,  it can be expanded across parallel buses using DMX splitters. DMX wiring  consists of a shielded twisted pair, with a characteristic impedance of 120 Ohms, with a termination resistor at the end of the cable furthest from the controller to absorb signal reflections.    Go read some more here.

Wiki also has a realy good graphic Simple DMX Network Bus

Traditionally the christmas lights fraternity add DMX terminators to each controller withe link pack to select the terminator if it the the last one on the bus.  I have added thenm to most of my designs too. For example X10 on my 8Ch DC Controller.

But here’s the rub.  I never fit the link packs.  I too lasy. and then I forget which one has the terminator installer.  So I so a for more visual termintator.

These terminators are a cinch to make and are pretty reliable too. the cost is super good.  the last lot cost me 6.5 cents each.

Material:

  • RJ 455 plug
  • 120 ohm 1/4W Resistor (1/8 W also work)
  • scrap Cat 5 wire insulation
  • hot glue ( optional)

Proceedure:

  • Bent one end of the resistor lead back over the body of the resistor.
  • Place the resistor on the outside of the body with the two leads alnign with the pins.  You want the body of the resistor to be just an the end of the pins.  Trim the leads.  I trim mine to XXmm.
  • Add some scrap Cat5 wire insulation to the resistors leads before inserting hte resistor in the connector housing and crimping.
  • Once your done, your can add a blob of hot glue or silastic the seal the end.

Just a coupleo of notes:

  1. 1/8W and 1/4W resistors are small and have 0.4mm diameters leads which is a tad smaller than Cat5 (0.51mm)  the body is also small enough to fit inside the connector housing
  2. There are two types of connectors dependant on your cable type, solid or stranded cable.  Try and purchase some connectors suitable for solid wire for this project.
DMX_Term5 DMX_Term4 DMX_Term3 DMX_Term2 DMX_Term1

 

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