Hello,

of course cabling DMX in a 'Y' shape is a big no, no, but since DMX is

"just" RS485 and RS485 allows for unterminated branch lines up to 5

Meters, maybe I could use 1m or so to connect a dimmer and save some

connectors I'd need to use for daisy chaining. Couldn't I?

Or am I misreading RS485 and missing the note about "branch lines are

only allowed for up to 1200 Baud"?

bye

Christian

Hello,

of course cabling DMX in a 'Y' shape is a big no, no, but since DMX is

"just" RS485 and RS485 allows for unterminated branch lines up to 5

Meters, maybe I could use 1m or so to connect a dimmer and save some

connectors I'd need to use for daisy chaining. Couldn't I?

Or am I misreading RS485 and missing the note about "branch lines are

only allowed for up to 1200 Baud"?

bye

Christian

On Apr 19, 10:51am, Christian Marg <christian.m...@tu-­clausthal.de>

wrote:

I once opened an LSC Tour dimmer. To find the In and Out DMX

connections just wired together, and then from the In connector to a

circuit board, total lenght of cable to the circuit board was under 2

inches. I would not want to risk it in a production environment.

Mike!

That's how most dimmers do it. Nobody y splits RS485 at the chip, it

would be pointless.

As far as unterminated branch lines no longer than a certain distance, I

think the idea there is that you don't want the total combined length of

wire longer than the specification states (4000ft), or else the signal

will have degraded so much from voltage drop to be unrecognizable.

Torrance

On Fri, 25 Apr 2008 12:54:24 +0100, Torrance Bell

<starlite528@yahooo­oooooooooooooooooooo­ooooooooooo.com> wrote:

You won't get a dmx signal down 4000' of wire though, it's more than

100KHz. You don't want branch lines as the reflected signal degrades

the original. Terminating them won't help as every termination gives

you at least a 3dB drop in signal.

RS485 is unlikely to go 4000' for Baud rates higher than 19200. DMX is

250kBaud and both ends of a DMX line should be terminated. This

prevents reflections from the unterminated end interfering with the

outgoing data. It is not generally recognised that the source end

should be terminated, but this is important and should be internal to

the master device. Measuring with a meter across the signal pins of the

source when the source is unpowered will tell you if it is correctly

terminated.

For all the information you never thought you'ld need about RS485

networks go here:

http://www.bb-elec.­com/technical_librar­y.asp

and download the first paper "Rs-422/485 Application Note".

Of course, DMX is only a protocol that runs on top of a specification.

It can most likely work with any digital signaling system that supports

at least the minimum data rate. I can only guess right now that they

chose 485 as the 'norm' is because of its simplicity, reliability, and

cheapness.

Torrance

On Mon, 28 Apr 2008 22:00:38 +0100, Torrance Bell

<starlite528@yahooo­oooooooooooooooooooo­ooooooooooo.com> wrote:

It was both.