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Topic: Using potentiometer to adjust resistance (Read 609 times) previous topic - next topic

nighterfighter

Hey guys, this is a really noob question, sorry-

I am trying to make a LED "dimmer" by using a sliding pot to adjust the resistance in the circuit.

I have the + side of a battery directly connected to one leg of the pot. I have my LEDs wired in parallel, then connected to the - end of the battery. My question is this-

Do I need to hook the Wiper end of the pot to the LEDs, or the other leg directly to the LEDs?

Here is a quick picture of what I have-

Thanks!

http://img251.imageshack.us/img251/6030/leddimmer.png

RuggedCircuits

Looks right, though perhaps not the most efficient way to do it. LED's are generally placed in series so they all have the same brightness (same current). You may see one LED quite a bit brighter than the others.

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nighterfighter


Looks right, though perhaps not the most efficient way to do it. LED's are generally placed in series so they all have the same brightness (same current). You may see one LED quite a bit brighter than the others.


Thanks for answering my question on the pot- I thought I should hook it to the wiper. So what should the other end of the pot go to?

Ah, thanks for that! I had a brain fart on the series vs parallel thing. I was thinking voltage determined the brightness, but of course LEDs are current driven!

Thanks.

RuggedCircuits

Quote
So what should the other end of the pot go to?


Nothing, or the wiper. We have a little writeup on this topic here:

http://ruggedcircuits.com/html/circuit__15.html

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nighterfighter

Thanks, that helps.

So just so I'm sure-

If I wire the LEDs in series, they will all have the same brightness?

RuggedCircuits

Yes, assuming they're all exactly the same (i.e., XX mA cause YY lumens). There will be some part-to-part variation but if they're the same part number the brightness should be fairly equal.

The drawback, of course, is that your voltage source now has to be at least as high as the sum of your LED forward voltage drops added up.

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nighterfighter

That won't be a problem.

Thanks for the help.

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