Using a DMX splitter

[niclights]

Oh dear. Another disastrous off topic adventure.

 

To try and bring things back to normality, you would not terminate unused outputs, but you can put a terminator on the 'thru since it effectively marks the end of that line.

[Ynot]

He may be referring to some which from the looks of the panels have a passive Y split between phase reversed and normal. So if you need a phase reversed output you don't need an external reverser. However using both would be equivalent to using a Y split on one output, with a phase reverse on one leg, which would be a bad thing.

Having re-read that post, of course that is correct!

 

When I first read it my mind saw it as "Don't use the straight output on one side of a splitter and the reversed output from the other" which of course is fine.

Duh!! ;)

[ben.suffolk]

He may be referring to some which from the looks of the panels have a passive Y split between phase reversed and normal. So if you need a phase reversed output you don't need an external reverser. However using both would be equivalent to using a Y split on one output, with a phase reverse on one leg, which would be a bad thing.

Having re-read that post, of course that is correct!

 

You know what, its not actually correct.

 

You can split a DMX cable at the source, and only right at the source (not after any distance from the source). This is because on an RS485 bus you can have a transmitter anywhere on the bus, not just at the start of it, so putting a split at the transmitter simply puts the transmitter in the middle of the bus. What you would need to be careful of, is that the transmitter does not have a terminating resistor hard-wired into it. If it did it would mean the bus was terminated in the middle!

 

You would of course need to terminate both ends in the this case.

 

Ben

[Ynot]

He may be referring to some which from the looks of the panels have a passive Y split between phase reversed and normal. So if you need a phase reversed output you don't need an external reverser. However using both would be equivalent to using a Y split on one output, with a phase reverse on one leg, which would be a bad thing.

Having re-read that post, of course that is correct!

 

You know what, its not actually correct.

 

You can split a DMX cable at the source, and only right at the source (not after any distance from the source). This is because on an RS485 bus you can have a transmitter anywhere on the bus, not just at the start of it, so putting a split at the transmitter simply puts the transmitter in the middle of the bus. What you would need to be careful of, is that the transmitter does not have a terminating resistor hard-wired into it. If it did it would mean the bus was terminated in the middle!

Erm, what?

You're saying that you can't split a DMX line remotely from the source (ie the desk supplying the signal)???

If that is what you're saying then I'm afraid that you are wrong!!!

DMX splitters are commonplace, and are used by multitudes of users, both amateur and pro.

Where I think you may be confused is saying that these are transmitters of DMX which they are most certainly NOT. These are simply optio isolators which allow the signal to be, well, split, without significant loss of data quality.

And I doubt that many splitters (if any) will have inbuilt termination facilities...

 

Oh, and the bit I was referring to as being correct seems to have no bearing on your response...

[mark_s]

If I read it correctly, I think he was trying to say that you can passively split a DMX line in such circumstances. But I may have got the wrong end of the stick too ;)

[ben.suffolk]

If I read it correctly, I think he was trying to say that you can passively split a DMX line in such circumstances. But I may have got the wrong end of the stick too ;)

 

Yes that was what I was saying. Sorry for any confusion, I figured as the bit I quoted was talking about passive splits it was obvious.

 

Regards

 

Ben

[steventaylor]

Thanks everyone for their comments...I seem to have opened a can of worms with some conflicting ideas but I have learnt a lot, as always, from those with more knowledge than I.

 

Steve

[Tomo]

You can split a DMX cable at the source, and only right at the source (not after any distance from the source).

While Ben is technically correct as regards RS485, this doesn't apply to DMX as every DMX source has a built-in hard wired terminator as it is required by the standard.

- That said, certain DMX sources can have this termination switched off (like ETC DMX Gateways), as they are designed so they can be used as receivers (not transmitters) in the middle of a line if required.

 

The simple and definitive answer is this:

 

DMX splitters (opto-isolated or otherwise) have two kinds of outputs:

A) Multiple "Split" or "Isolated" outputs, which are DMX sources just like your lighting console, and thus all the ones you use require termination at the end of the line.

B) The single "Thru" output, which is part of the original daisy-chain from the upstream source and thus requires termination just like any other DMX-controlled fixture whether it is used or not.

 

In general, it's good practice not to use the "Thru" output to feed anything that's some distance from the splitter - so either don't use it at all or just feed another splitter in the rack with it.

This is to ensure that faults on distant things don't affect the rest of the system, so you can more easily locate problems.