DMX Questions

[david.elsbury]

Hi there

Install questions again, if you don't mind. Thanks :P

 

1. I have already decided that DMX will be run to each bar via a DMX splitter for ease of adding movers and scrollers and such.

Assuming I'm using an opto-isolated splitter (which I will) is is neccesary to terminate each line when not in use? So at each socket on the bar, do I need to have a terminator? I can see these getting lost/ not put back etc. What will happen (if anything) to my data?

 

2. If I leave the dimmers on all the time (will be) and I turn the desk off, there is a possibility of random data coming down the line and some channels turning on by themselves. Experienced that one. What can I do to stop this happening? A custom built box that, when the desk is off, shorts the data to ground on the DMX lines to the dimmer? I would prefer not to leave the desk on if I can help it, wear and tear and all that.

 

Thank you

David

[dbuckley]

If there is no terminator on a bar line then data on the line after the split may be garboiled, but it doesnt matter as there are no fixtures there. What cant happen is corruption to "leak" back through the splitter, so all OK.

 

If you want to keep your DMX512 line silent, short the A and B (+ and -) lines together, but not to ground - ground has nothing to do with DMX512 data.

 

What would also work and is less messy is a termination resistor at the desk end. A RS485 circuit (which is what DMX512 is) should have a terminator at both ends, but as one end is always driven it is often omitted. Measure the desk when off across the A and B lines with an ohmmeter, if it's not about 120 ohms then add a resistor into the plug that goes in the desk.

 

Speaking of opto-isolated DMX splitters, £58.78+VAT buys you a 4 way isolated splitter, something of a bargain, unless you know better? I parted money for one of these, and it does exactly what it says on the box.

[peter]

If you do require on-bar termination, what about attaching the terminator to the bar with some sort of safety bond, crimped around the bar? That way, the terminator can't walk, and is always close to the socket. When de-rigging the fixtures, just replug the terminator and you'll keep a clean feed.