3w RGB stars - wash fixture

topjimmy

Member
The individual star 3w RGB leds have come down in price quite a bit so I purchases a bunch, specs are (R=2.5, B=3.5, G=3.5) 350ma per channel. I'd like to make several wash fixtures each with 6 of these RGBs and single DMX addr per fixture. I was planning on using one of these DMX512 Decoder Drive Controller PX24506 3A 3CH 256 Level Brightness Full Color L | eBay for the 1st fixture in the daisy chain bc it outputs DMX, then use these cheaper DMX controllers on the 2nd,3rd fixtures 3 Channel RGB DMX Controller - 12v DC / 6 amps w/Bare Lead Input & Output these only listen for DMX input and don't relay it, hence the need for 1st listed controller above.

Most of these DMX controllers (assuming) output PWM, vs SPI..etc ? In order to build the fixtures I need build drivers inputting/understanding PWM. Per fixture is 6 RGB, = 18 leds, are they any IC's chips (TLC2950 24ch but inputs only 1 pwm ch per chip I believe), there's the CAT4109 with 3 pwm inputs and 3 led outputs though output per ch is 175ma and I need 350ma..could amplify to achieve 350ma I think. (The IC would need direct pwm inputs). My questions are I'd like to use 3 ICs (1 per color) for a single fixture, versus, 18 ICs (3 per RGB) to simplify the design. In using only 3ICs per fixture the IC would need rating of 2amp (6*350ma), The voltage coming out of the DMX controllers will need to be regulated via constant current circuit, any advice on such a build?


Thanks
Jim
 
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I am having a tough time following what you are going for, but let me see if I can clarify.

Most of these controllers probably output PWM, as thats pretty common for these low cost LED controllers.

I am unclear as to your reasoning for needing the DMX out? If you are concerned about the daisy chain, each controller can have a DMX in and out, as long as the "stub" is less than a few inches long. (I forget the amount allowed by DMX Spec)
If you are expecting the 3A controller to generate DMX for the others to follow, I don't believe that is how that device works. You would still need a control console of some type to add control.

I also am unclear as to how you intend to "amplify" to achieve 350ma.

The easy item is the Constant Current Circuit. The best way to achieve this is by supplying the fixture with a constant current power supply.

I don't know much about the items you are thinking about using, but if it were me, I would take a look at the following power supply and DMX Decoder
DMX Decoder
Power Supply (Get the 150 watt one)

These might be a good starting point for your needs.
Good Luck!
 
fyi, I found out you can't run RGB's in series to your driver if they are common anode,which was one of the questions I had.

The cheaper 3ch DMX RGB controller from holiday coro are only $8 but don't relay DMX, if make the first fixture in the daisy chain run having a controller that outputs/Relays DMX than I can just run this line down the run to each of the listening DMX controllers, so, just have a Y splitter. This way each fixture can have it's own DMX address. Supposedly, you can run DMX 1500 ft before needing an amplifier, ought to work fine.

I do need some type of constant current driver, since I can't do RGBs in series, I'd need 3 drivers per RGB star, or in my case 6*3=18 drivers each doing 350ma, since I'll have 6 RGBs per fixture. I was hoping to find a multichannel Integrated Circuit that does constant current with additonal resistors, capacitors..etc. It can get pretty complicated, but, there's are numerous ways to do so very cheaply such as using LM317's.

I was hoping someone has been down this road before, there's just so many ways to do it, such as with an arduino..etc



I am having a tough time following what you are going for, but let me see if I can clarify.

Most of these controllers probably output PWM, as thats pretty common for these low cost LED controllers.

I am unclear as to your reasoning for needing the DMX out? If you are concerned about the daisy chain, each controller can have a DMX in and out, as long as the "stub" is less than a few inches long. (I forget the amount allowed by DMX Spec)
If you are expecting the 3A controller to generate DMX for the others to follow, I don't believe that is how that device works. You would still need a control console of some type to add control.

I also am unclear as to how you intend to "amplify" to achieve 350ma.

The easy item is the Constant Current Circuit. The best way to achieve this is by supplying the fixture with a constant current power supply.

I don't know much about the items you are thinking about using, but if it were me, I would take a look at the following power supply and DMX Decoder
DMX Decoder
Power Supply (Get the 150 watt one)

These might be a good starting point for your needs.
Good Luck!
 
Constant current is much more complicated than just adding resistors or other components. It is a core feature of the power supply that drives the entire circuit.
I am still confused about why you need a dmx out on the "first" fixture. As far as I can tell, that unit doesn't have any per built programming to output, isn't it really just a data passthrough?

And I wouldn't expect you to be able to drive the LEDs in series, you would want to drive them in parallel at the appropriate voltage for the LEDs you select.
 
Most dmx devices just tie the inputs and outputs together on a pcb board they do not retransmit data, just pass it straight through.
 
There's a few ways to build the drivers for each RGB, current restricting, constant current...etc and have pretty good idea on what is needed, I'll post the build out after doing so bc I think alot of folks would be interested, est about $2 or so per driver/per RGB.

I suppose, if I didn't use the 1st RGB Controller with DMX out, how could I use the cheaper one in its place? It has DMX-in, power-in and output, each of these controllers has it's own address programmed via pc application beforehand. If I tried to use the "output" and put a "Y" splitter on it and ran it to the 2nd fixture's DMX controller's DMX-in, this might work, however, I'm assuming
the "output" of 1st DMX controller will have adjusted voltages/current according to the DMX signal sent to it, as it's output is 3 wires R,G,B and not DMX+/- ground format. So wouldn't the 2nd fixture get the converted signal(pwm) from the 1st fixture then instead of true DMX signal? I'm thinking it needs to be the raw DMX +/- signal unconverted yet... does this make sense?



Constant current is much more complicated than just adding resistors or other components. It is a core feature of the power supply that drives the entire circuit.
I am still confused about why you need a dmx out on the "first" fixture. As far as I can tell, that unit doesn't have any per built programming to output, isn't it really just a data passthrough?

And I wouldn't expect you to be able to drive the LEDs in series, you would want to drive them in parallel at the appropriate voltage for the LEDs you select.
 
I think you are over thinking the DMX out on the 1st RGB Controller.
It really is just a mis-labeled Pass through, and the exact same thing as the other controllers in a Y configuration.
The "output" of the first controller is not adjusted at all, and it is simply passing the data through to any other items in the data chain.

The only real difference between the 2 items you list is the maximum amperage per channel, and that one is easily addressable via Dip switches.

All the controllers would be controlled by DMX, none of the items you list are able to be controlled by PWM.
 

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