AC PWM Control on DC Lighting

Discussion in 'The Projects Forum' started by KB1SPH, Aug 29, 2012.

  1. KB1SPH

    Thread Starter New Member

    Aug 28, 2012
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    OK, bear with me, I'm not the greatest at electronics, but I'm learning.

    Here's the setup. I have a Light-O-Rama light controller for my Christmas light display. This controller can dim the Christmas lights with settings between 0 and 255. From what I understand this is done with PWM instead of varying the voltage like you would with DC. I want to make a custom set of RGB LED lights, but I'm thinking of running them off of something like a 12v source instead of trying to add up enough LEDs to make them run off the 120 with diodes. This would allow me to make each section of lights to a custom length instead of having to have a fixed number of LEDs in the set.

    So, my question is, how would I take the PWM on the AC source and convert that to a variable DC output? Ideally whatever varies the DC voltage would not be restricted to one voltage (of course it would have a max), but could be used with perhaps 5v or 12v and have enough current for maybe 200-300 LEDs.

    Any ideas would be appreciated.

    Thanks,
    Jeff

    NOTE: I do have some experience with PIC controllers if there is some way of the PIC reading the PWM from the AC and then controlling a LED control chip. It's the reading the PWM that I don't know how to do.
     
    Last edited: Aug 29, 2012
  2. wayneh

    Expert

    Sep 9, 2010
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    There's a chance that your device uses DC PWM internally. Hard to tell.

    Anyway, you still want PWM if you're using DC. Varying voltage is NOT a good approach for this. The voltage spread for an LED might be only 0.5V or so, from dark to burnt out. PWM gives you a way to vary the time-averaged current, and that's what controls brightness. For example, a generic LED changes from dim to bright in the current range of 1 to 25mA.
     
  3. KB1SPH

    Thread Starter New Member

    Aug 28, 2012
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    Hmmm, ok. Someone told me that PWM wouldn't work for the LEDs, I had a feeling it would. The easiest thing for me to control the LEDs with is a PIC chip controlling LED controllers within the strip, but I'm not sure how to read the PWM from the AC coming out of the Light-O-Rama controller. I also don't want to modify the controllers I have, they're not cheap and I do have some regular lights to control with it as well.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Yeah, that's dead wrong. :( PWM is the "state of the art" for LED brightness control.

    If you want to use your existing signal, you need to define what it is. Some of the devices on that site use triacs, others use DC PWM. Either way, I'm sure folks here can help, but not by guessing. See what you can find out as far as specs, model numbers, rated outputs, whatever.
     
  5. KB1SPH

    Thread Starter New Member

    Aug 28, 2012
    4
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    OK, this is basically the model I have, except mine also has the built-in MP3 director.

    http://store.lightorama.com/locolico.html

    They used to have a DIY kit you put together yourself and it had a list of the part numbers, but I can't find it. I might have it on a HD somewhere. If not I'll have to open up one of the boxes and see what's inside. I have an appoint I have to get ready for right now, but I'll post another reply later when I have more info.

    Thanks,
    Jeff
     
  6. KB1SPH

    Thread Starter New Member

    Aug 28, 2012
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