LTECH DMX Decoder

[Peter]

Just taken delivery of a DMX 8 channel decoder / driver

I can see I need to set the channel which appears straightforward, however the DMX bus is a RJ45 connection which wasn't what I was expecting.

Looked on the internet and it appears that the wiring for DMX 512 over Cat cable is the T568B standard

https://www.medialon.com/support/faq/how-to-convey-dmx512-over-rj45/

But clearly the Loxone Bus is just two wires (DMX - and DMX +)

I'm surmising from the link (above) that I need to wire orange and orange white (primary data links) to the Loxone DMX bus?

There is of course no way to wire the resistor into a RJ45 connector!!

Grateful if one of you guys can confirm my summary is correct.

Edit: 

It's now also occurred to me that I don't know how to add this driver in the Config file.

I can click on the DMX Extension which gives me the option to add a DMX advice but how do I add a 8 channel driver? 

I intend to use 4 of the channels for RGBW spots and the remaining four for a RGBW LED tape.

[Duncan]

firstly dmx is 3 wires, the plus, minus and earth/common

many dmx devices use rj45 and its usually clear on the case or documentation which pins are used, but its usually
pin 1 positive orange/white
pin 2 negative orange
pins 7/8 earth/common. brown/white and brown

to wire in a termination resistor, simply cut the plug and a short length of cable from a standard cat45 network cable and solder the resistor between pins 1 and 2 (orange/white and orange)

you dont need any 'drivers' for dmx, only to add the dmx devices to your config

for your install, click on the dmx extension then add a dmx from the top menu - select rgb and w which will add a 4 channel device, then you just need to manually set the address to the start address of your 8 channel device

next add another rgb and w device, but set the address in loxone to the start address of your device + 4

[Peter]

Hi Duncan

Thank you for the explanation.

Assuming my own thoughts were correct I had got as far as wiring the orange / white and orange to the DMX bus and using a RJ45 on the other end to connect to the decoder (without a resistor).

Also wired the RGBW spots to the first four channels (and the +)

Did exactly as you said for the config file (except the second part for the next four channels).

Set the channel to 13 which is my next available channel (on the decoder and in the config file)

However the decoder is continually flashing blue, which suggests an error. I'm not certain but I don't think the lack of a termination resistor would stop the decoder working at all, but ready to be corrected.

[Duncan]

the terminator resistor wouldnt result in an error within the dmx decoder, and many times the system will work without anyway unless you are running huge lengths such as 500m plus of cable.

does the decoder work? the blue flashing light indicates its getting dmx messages i think - ill check with my ltech decoders to see

just checked - my decoders have a green led by the side of the address selector switches that flashes around twice per second when they are receiving a dmx signal

[Peter]

Hi Duncan
Haven't had a chance to work on the lights today but will do so tomorrow and report back.
Thank you for the info.

[Peter]

Everything now working, thank you.
One final wrinkle though
The decoder is powered by a separate supply from the Mini server. When I power off the server the downlighters default is to illuminate, I expected the opposite.

[Simon Still]

What was the problem?  One of the things I don't like about DMX is the lack of any real diagnostics - if it doesn't work it's hard to work out what the issue is.

On your 'default to on' lights - why would you have the miniserver powered down once installed?  Could you use the miniserver to control power to the decoder power supply? 

[Peter]

Simon, to be honest I'm not entirely sure what the problem was. With the exception of not fitted big the termination resistor I'd already done what Duncan subsequently suggested. I can only think I'd made a Config file error, but I don't recall making any changes.

I'd powered down the mini server to fit some Tree stuff and noticed the lights were on. The power supply for the decoder is independently wired from the server as it's in the loft (to eliminate voltage drop issues)

[DavidL]

DMX devices can be set to do various things when they loose DMX data.

In your instance, I suspect you had the lights on before you powered down the miniserver. Once powered down, and no DMX data was being sent, the DMX decoder is most likely falling back to last state on DMX loss. 

You could prove this by powering your miniserver back up, setting the lights to off, and then turning the miniserver back off again (or unplugging the DMX cable).

If they still come on, then you might have a decoder thats been set to turn all outputs on to full on DMX loss as a safety measure.

David