DHA Digital Light Curtains

[Chris Davies]

Hi,

 

I am working on a show and am using 7 DHA digital light curtains (evil sporn of satan things) and one of them has decided that it will work fine as long I want Green, Green or Green as a colour (incidentally I don't).

 

I have tried a couple of things to solve the problem but no joy as yet:

 

Swapped the scroll on it

Retentioned the scroll

Given all the sensors etc a good clean

 

Just wondering if anyone has thoughts on what the problem might be.

 

Cheers

 

CHRIS

[WiLL]

well, presuming it's reading it's DMX alright, and you've done all the normal diagnostics on the control side of thing... maybe it's just buggered? If it's a hire unit just demand a replacement, if it's in-house curse and stamp your feet (and possibly 'accidentally' drop something on an actor)

 

 

 

 

*This forum does not condone the dropping of objects onto actors wether accidentally or not even, and let's be absolutely clear about this, even chorus members*

[Pete]

My personal preference is to drop the dlc in the bin!

[Chris Davies]

If it was mine to drop in the bin I would.

 

Actually I would never have used them in the first place thinking about it!!!

 

The biggest problem I have is that there is a spare sat downstairs in the store but it is not progammed (arse!)

 

CHRIS

[Nicktaylor]

Not having used them, I am not sure what the problem is with using the spare. Dont you just set the DMX start address on the extra unit and away you go ?

[SimonW]

You can calibrate where the 'start' and 'end' positions of the tilt are, but only by connecting them to an Apple Mac

running the LightTalk control software.

 

If you're using the DMX->LightTalk convertor, then you're stuck with whatever the end stops were set to by the hire

company. If the end stops between the broken unit and the spare don't match, then the Light Curtain won't point

where you want it to.

 

The Light Curtains also don't have DMX address switches in the usual way - they auto allocate addresses to themselves when they are first reset - you just address the DMX -> LightTalk convertor with a start address for the whole block

of Light Curtains that it controls.

 

Simon.

[WiLL]

You know, that just sounds like the dumbest, most inflexible way to design a DMX fixture I've ever heard of.

[Rob Halliday]

Ah, but there's the thing: they weren't designed as DMX fixtures.

 

Their 'natural' language is LightTalk, a lighting control language developed specifically for them. When it was designed (late eighties, early nineties) - and in fact, to this day - it offers all kinds of advantages over DMX. It's bi-directional - the DLCs can talk back. It didn't need any addresses set on the units (each has its own unique serial number; you patch at the control computer). It was based on real units (you said 'rotate 10degrees downstage' not 'turn 20 DMX steps') And it's 'resolution independent' - you say 'turn 20 degrees over 5 seconds, go' and the DLC does it. Incredibly smoothly, and incredibly accurately.

 

You can also use it to control the behaviour of the DLC. So, for example, if you rig ten DLCs and they're not quite perfectly aligned with each other (which is really obvious with a DLC) you don't have to get to the bar and jiggle their rigging, or constantly shuffle their positions from the console. You just use the LightTalk Mac to move them, by fractions of a degree, until they're all aligned. Then you say 'that's your zero position'. Imagine if you could do the same thing with other moving lights rather than having to constantly re-do many, many preset-focuses.

 

(DHA's Digital Beamlight had the same functionality, but expanded so that you could set any position and the limits using DMX. So when FOH rigging means that the lights got hung 90degrees round from their usual position you just put the light in its line-up cue - say pan 43/tilt 22, put it into 'adjust position' mode, adjusted it so it was pointing to the usual line up position , then said 'ok, that's now the position that corresponds to pan 43/tilt 22. Since all of the other positions were relative to that it'd be about right for every other position it did in the show without having to re-plot all of them)

 

 

Setting the end-of-travel positions on the DLC was a solution to the fact that when the DLC DMX adaptor came out most consoles didn't support 16 bit DMX operation. On 8-bit, 255-step, control the DLC's movement became steppy over it's range of travel. However, for most shows you wouldn't want the DLCs pointing to the ceiling - or, in fact, travelling much past 45degrees either side of vertical. So you limited their travel to +/- 45 degrees; the DMX converter box then re-scaled the DMX steps so that 0-FL covered just this 90 degree range of travel, so giving you higher resolution control.

 

There is also a similar intelligence applied to the scroller in the DLC, so DMX 5% (or whatever the value is) is always frame 1, regardless of whether you have 5 frames in the scroller or 20. So, again, if you change the length of your scroll you don't have to replot your show.

 

 

Now, of course, consoles are better at handling moving lights and the use of the DMX interpreter does make the DLC a bit quirky - particularly in the situation described here where a spare is sent out with the wrong limits set (-you should complain to your hire company about this) and with no Mac on site to do the setting. But being able to re-zero the unit remotely is still a great time saver in many situations.

 

Plus just because DMX is more common doesn't mean it's better. The DLC was ahead of its time, and it's interesting to note that many of its features will also be core features of the new ACN control protocol, coming soon to a lighting desk near you (hopefully). For example: patching from the console without having to set addresses on the units. Efficient use of control system bandwidth ("do this GO" rather than "be at position 102, 102" repeated hundreds of times a second, which is effectively what DMX is doing). Possibility for controlling in 'real world' units rather than arbitrary steps. And bi-directionality - with the light able to tell you it has a problem before it screws up a cue. (Some of this may of course be because Philip Nye, who designed LightTalk and the DLC, is also on the ACN committee.)

 

Once that gets established, we'll all look back and think that DMX was a pretty dumb way to control a lighting fixture....

 

As you may be able to tell, I like DLCs...... because they're clever, and also because they produce a beautiful light that nothing else can match.

 

Rob.

 

 

(PS: Though LightMoves, DHA's control software, only runs on a Mac - and, increasingly, only on older Macs since it needs a serial port or a USB-serial adaptor plus OS X's 'Classic' environment to run in - there is also a program called LightChat which lets you use a Psion hand-held computer to configure the DLCs. Of course, Psions are now also quite rare....)

 

(PPS: There is a persistent rumour that Rosco, who now own DHA and so the DLC, will re-design the unit to give it on-board DMX control.)

 

(PPPS: As to the original question (!), Chris: is the scroll not moving at all - ie. it's always stuck in green - or is it moving under manual control but always seems to end up in green?)

[Chris Davies]

Thanks for all the info Rob

 

Managed to work around the problem in the end and the broken DLC is back with the hire company being looked at.

 

Thanks again.

 

CHRIS