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That was a great post. I'm in a similar situation and I was wondering if you could give me some more info.
I got some LED strings which supposedly had a twinkle effect, but when they arrived it was more like a strobe light effect.
I already got an Arduino UNO and a relay so I would be able to turn the lights on and off remotely, but now I'm thinking that I could create the desired twinkling effect using the Arduino too.
My limited understanding is that the lights (which are mains power in my case) are powered via a bridge rectifier to DC, and there are effectively two channels of live and one ground wire.
I didn't know anything about this stuff when I started the project; if I had, I might have gone with one of those fibre optic setups that has LEDs reflected off of a rotating disk into the fibers to create a twinkling effect. However, I want to use the stuff I already bought, so I understand the effect will be pretty limited with only 2 groups to control.
I'm interested in how controlling these groups would actually work and what the easiest way to do that might be.
You mentioned that one can only control a few LEDs per PNP transistor. How might I go about controlling a whole string? Mains voltage is 220-230v here.
I was thinking a possible solution would be to control two PNP transistors (for the two channels) via the UNO's PWM pins, and then use the transistors to control a solid state relay, but I have no idea if that would work or how rapidly that type of relay can be switched. I was surprised by how loud normal relays are when I was testing mine, it's fine for on and off but it will be annoying to hear all the time when the lights are on.
Another, possibly simpler solution would be to piggy-back on the existing controllers. Watching one of bigclive's videos on YouTube, it seems like the effects are generated from the DC pulses themselves, using whatever the polling rate is (50hz?) as a timer. There seems to be a little controller in there on a perpendicular board but it's potted with epoxy so I can't get at it. If you think this would be a viable solution I can take some pictures of the board as I'm not really sure what I'm looking at (apart from the rectifier, controller and a few capacitors).
I've really been struggling to find info relevant to my specific case so I'd be super thankful if you would help me out.
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Posted:Nov 3, 2012
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