Control/Dimming DMX controller that is capable of pulsing in milliseconds

Discussion in 'Lighting and Electrics' started by DSh, May 16, 2016.

  1. DSh

    DSh New Member

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    Hi,

    I am new to this page but it seems like the right place to get my questions answered... I need a DMX controller that is capable of pulsing in milliseconds. I need to pulse LEDs at the same on-off frequency, so nothing complicated but I need a device and a piece of code that will allow me to do that. Where could I find one for cheap and that is easy to use?

    Cheers,
    D
     
  2. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    DMX doesn't do milliseconds. It's not that speedy. Maximum refresh packet transmission rate for a full 255 byte frame is around 44Hz. I suppose you could try to do something creative with bit patterns in the frame but that seems like an odd way to do it and you'd have to deal with the interframe gap somehow.

    Pulsing in milliseconds would typically be handled in the driver circuit for the LED. If you're trying to do PWM dimming then you'll need some sort of DMX-to-PWM converter, assuming DMX has any reason to be part of this application.
     
  3. JD

    JD Well-Known Member

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    Add to that that device reaction time is much slower then the full frame rate and you can see the outcome would not be what is desired.
    Although the TX receiver may be able to port a new value 44k times per second, that information is then processed by the microprocessor in the fixture. Most of them are notoriously slow. Also, since there is no error correction in DMX, the processors often emulate virtual error correction by using the "Did I just see that value last frame?" technique.
     
  4. n1ist

    n1ist Well-Known Member

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    What exactly are you trying to achieve? Strobing and precise timing is probably better to handle in the driver (instead of the controller)...
     
  5. DSh

    DSh New Member

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    Hi ,

    I have LED strips that need to be connected to a controller that can handle 12 DC voltage. However, the controller only powers the lights. In addition, I need to strobe the lights. This has to be at a precise -ish frequency of milliseconds.

    I have built a bio-reactor that is powered by LEDs to grow algae, I am manipulating light flashes to get a desired outcome. I haven't been able to find a device that will do what I need it to do. I am good at building stuff and the science that goes behind my experiment but not the most tech-savvy when it comes to doing this part.

    Help! :))

    Is there any other device you could think of that would be able to do what I need it to do?

    I was looking at this controller to power my LEDs (check the link below). I need it paired with some sort of an apparatus that will strobe the light for me at the desired frequency.

    http://www.ledsupply.com/led-drivers/quadpuck-4-channel-dmx-constant-current-controller

    http://www.ledsupply.com/led-drivers/quadpuck-4-channel-dmx-constant-current-controller

    This is the controller I was looking at to power my LEDs. It has enough drive to power them all in one unit. I can daisy-chain them together. Is there something that will have this plus allow me to pulse the light at the frequency I want?
     
    Last edited by a moderator: May 18, 2016
  6. Brentgi

    Brentgi Active Member

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    Controlling and dimming are two different, yet related, concepts. At least in the theatrical/performance world.

    If I understand you correctly, you don't have a complete LED fixture, meaning there is no 'computer' inside the LED strip that tells the lights what to do...

    With a typical LED fixture (pro or even "DJ" grade), most of the work is done by the fixture itself and the controller is just telling the fixture which operations to perform. For instance, if I have an LED strip that I want to strobe, I will have the controller send a message to the fixture that tells it to strobe. The fixture will then strobe. The strobe feature, however, is actually being controlled by the fixture and not the controller.

    It's like me telling you to jump at intervals, and I can even tell you to jump at specific intervals (i.e., once every second). And do this until I say otherwise. But I don't send you the command to jump every second. Does this make sense?

    So what you'll need to build is a fixture that handles the actions, and you'll want a controller that can send a command for that action. Also, I'd suggest digging into DMX and how it works. You'll find it quite helpful.
     
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  7. TJCornish

    TJCornish Well-Known Member

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    You need an LED driver, not a DMX controller. Unless you have some need to connect to a theatrical lighting control system, you'll probably have better luck on an electronics forum asking about micro-controller-controlled PWM. The Arduino platform may be a good starting point as they have a lot of add-on hardware options including PWM drivers for things like stepper motors that may be adaptable to what you're trying to do.

    You may want to ask here: http://www.eevblog.com/forum/beginners/
     
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  8. DSh

    DSh New Member

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    Hi TJ

    I am trying to figure out that forum but wasn't able to find a category appropriate for answering my question. Would you be able to suggest one?

    D

    Would you be able to suggest where I could find the controller and the fixture for this particular application? I could really use any help I can get with this.

    D
     
    Last edited by a moderator: May 27, 2016
  9. n1ist

    n1ist Well-Known Member

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    I don't think there's anything ready-made for your application. Probably the quickest way to build this would be an Arduino and a n-channel mosfet (something like this: https://www.sparkfun.com/products/12959 would work). It will take some soldering and some coding. As others have pointed out, the Sparkfun or eevblog forums are probably better places for this project.
    /mike
     
  10. TJCornish

    TJCornish Well-Known Member

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    I would suggest the beginners forum that I linked to. I don't know of a packaged system that does what you want, so unless you can find one, you're going to need to do some legwork yourself. There are a lot of potential solutions. One general direction that has a large community is the Arduino microcontroller. They have IO pins that can pulse outputs. This project deals with pulsing LEDs, and while probably not exactly what you want, might be a component, or at least a starting point:

    https://github.com/prampec/arduino-softtimer/blob/wiki/SoftTimer.md

    Here is a stepper motor driver which is really just a high-current pulse source:

    http://txapuzas.blogspot.com/2009/12/paperstepperunipolar-driver-de-potencia_12.html

    Asking around in the EEVBlog forum or other Arduino communities will probably get you better hits.
     
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