RGB LED Tape - 8m long?? DMX??

[cameroncoats]

I do enjoy that chip though. Nice fast PWM as well so you dont get odd effects when it moves. I've got like 20 metres of the RGB pixel tape at home and currently have it dangling on my door. Nice stuff.

Controlled from a suitable chamsys desk I'm sure? :P.

Tried running about 40ft of it from my PC wing today… but the cue stack didn't seem to like running at 2000bpm and kept "freezing" and needed to be opened, the next cue selected, then goto cue pressed.. Oh well, I had fun with it :P

Edit: snipped quote

[Happy Jack]

Bumping an old thread, as I'm currently having a good old look in this general direction.

 

I've hit something of a brick wall with what limited knowledge I possess. While this feeds into a bigger picture, I'd like to know how one would achieve 'master intensity' dimming over an entire array of LED's. The closest I've come is via this application note for the from Maxim which details the switched-LED power-supply technique and hierarchical relationships; is that how one would achieve it?

 

http://www.maximintegrated.com/datasheet/index.mvp/id/5278

 

Given the selection of a appropriate micro-controller and the requisite firmware, then extending the DMX channel count from 3 to 4 with a handle over master intensity can be achieved?

 

Surely if that were the case there would be a plethora of DMX RGB controllers with this function? Clearly I'm missing something here...

[Wol]

"master intensity" is either a function of the LED controller or the lighting desk you're using.

 

For some RGB tape, it's just a proprietary protocol being transmitted which is just a raw RGB value. The controller boxes for these, dependent on the manufacturer, will either have just a three channel DMX profile for them, and not provide a master dimming function, or will be nice and provide a master dimmer, and it will multiply the RGB values by the intensity value.

 

For fixtures which don't have an actual dimmer channel, then some lighting desks will allow you to patch a "virtual" intensity channel for the fixture. For example on MagicQ, you can patch an LED fixture, and then patch a dimmer channel to act as a master. The multiplication of the RGB values is then handled in the lighting desk before the DMX values are sent out, rather than after the DMX values are received by the LED controller.

 

Does that make any more sense?

[Happy Jack]

Thanks for the response Wol, I enjoyed the MagicQ reference.

 

...it will multiply the RGB values by the intensity value.

I suppose I'm trying to discover what 'it' is; that so few low budget off-the-shelf controllers provide this function had led me to conclude one of two things. That it is hard to achieve. Or that it is expensive to achieve. That doesn't appear to be the case.

[Wol]

I'd imagine a lot of LED controllers will only provide 3 channel control because they assume that you're using it with a modern lighting desk which can provide premultiplied values to the controller. It is also an "expensive" operation in terms of CPU time having to postmultiply every value considering for what is usually a fairly low power / cheap microprocessor in the LED driver. If you just use direct values, you're literally just reading bytes in off the DMX line and pretty much just throwing them out to the PWM driver. To then add the "virtual" dimmer functionality, you're then having to loop back through the DMX line and multiplying each value in chunks of three.

 

It also involves the person who is writing the firmware to actually give a s**t about it! There's a reason that some of them are on the "low budget" end of things ;-)

[Happy Jack]

I'd imagine a lot of LED controllers will only provide 3 channel control because they assume that you're using it with a modern lighting desk...

Thanks for that, Wol. I'll have to now admit, I own a basic MagicDMX dongle but have yet to explore the software. I'm now aware of the 'Merge' and 'From' fields that enable this virtual dimmer. My message is in response to a request that would certainly benefit from that functionality, so I will certainly recommend they have a good look at MagicQ if is to be something they require. It appears that I should do the same.

 

It also involves the person who is writing the firmware to actually give a s**t about it! There's a reason that some of them are on the "low budget" end of things ;-)

I've had a look at the ASM for Hendrik's 9 channel PWM driver. As something of an introduction to AVR programming, it doesn't appear too daunting.

 

Thanks again, Wol.

[peternewman]

Seeing as this has been bumped again, it's probably also worth mentioning you can now drive your WS2801 or LPD8806 from a Raspberry Pi using OLA (Open Lighting Architecture); see here for more info. ArtNet, sACN or a number of other IP protocols as input, or add a dongle for a physical DMX input. It even includes RDM to configure it remotely!