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Discussion Starter #1
I know there is an abundance of info out there, but I cannot seem to find precisely what I am looking for. I have an old computer power supply that I use for lighting some of my pumpkins, and I want to make them flicker. I know that I could just add a flicker led to the circuit, but instead of redoing all of my work so far, is there a simple circuit I can build from parts I could find at radio shack?

Now come the more difficult part. I have a home made power block (think ac power strip) that I send one cable from the CPU power supply to, and then all the less have wires running from that. Can I build a circuit into the line before I split it, or must they be in line with all of the individual lights?

I hope I have explained all of the well, and just for reference, I am using the 5v output to drive the leds.

Thanks everyone in advance for the help.
 

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Your simplest option would probably be to use a circuit like this, from this article, substituting your set of parallel LEDs for the 1 W LED and 2 Ohm resistor in the diagram. The downside of doing it this way (and it will apply to any solution that doesn't involve separately wiring each LED line) is that the flicker will be exactly synchronized across all of your pumpkins, which may look a little weird. You definitely want to put the flicker on the 5V line, not the mains line going into the computer power supply; the PSU won't take kindly to an intermittent 120V AC voltage in the long run, and you likely won't get the result you want anyway.
 

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Discussion Starter #3
Thanks CDW. A follow up question for you then. Do I have to use the flickering led, or is there a way to build the flicker part. I only shy away from the led itself due to the way that I have the leds mounted in the pumpkins. I'm not opposed to adding separate circuits on my output lines, but the extra led would look odd since the wire runs are fairly long. Thank you again.
 

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Thanks CDW. A follow up question for you then. Do I have to use the flickering led, or is there a way to build the flicker part. I only shy away from the led itself due to the way that I have the leds mounted in the pumpkins. I'm not opposed to adding separate circuits on my output lines, but the extra led would look odd since the wire runs are fairly long. Thank you again.
You can build your own DC flicker LED circuits (google around and you'll see them), or find an old LED tealight from before they started using integrated flicker LEDs, but it's immensely easier just to use a flicker LED. I'm not sure exactly what the problem you're describing is; if you use the circuit I linked to, you can just put it on the 5V line right next to the power supply, split off the output to each of your pumpkins just as before, and cover the flicker LED with electrical tape, since it's not part of the display.
 

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Alternatively, if you want to avoid the synchronized flicker problem, you can build a separate one of these circuits for each of the separate lines, and put them after the split on the 5V line, but still next to the power supply with electrical tape on each of the flicker LEDs. It'd be nice if you could just stick the flicker LEDs in series on each separate line, because that would make each pumpkin flicker independently with a minimum of components, but you'd have to change out the resistors on each of your pumpkin LEDs to account for the new voltage drop from the flicker LED, and it sounds like you'd prefer to avoid that.
 

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Discussion Starter #6
Thanks again CDW. I still have a question about the circuit you linked to. With the led/resistor group that I have already created and mounted in the pumpkins, if I use the circuit as designed, am I using my leds as the 1W led in the diagram, or is that in addition to? I'm not so great with the electronic components or understanding them so far, so I'm trying to make sure I don't just burn everything out. I appreciate all your time in walking a noob through this. :)
 

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Discussion Starter #8
Does the transistor have to be as large as the one in the schematic? Its a hard one to find in store for me here, whereas there are smaller current ones more readily available.
 

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That would probably be fine - you can get a good sense of how much current your LEDs are using by counting how many LEDs you have in parallel (excluding any stacked in series), and multiplying by 20mA. However, if you use a different transistor, you may or may not have to fiddle with the value of that 620 ohm resistor to get it to turn on properly.
 
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