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I originally ordered a bunch of prewired 5mm ultra bright LEDs that had resistors already soldered in place to run off a 12V DC power source. I was going to make four sets each of a different color ie: 10 white spots, 10 green ones, 10 blue ones, and 10 violet ones. They were going to be set up for my Halloween display. Pretty easy stuff. But now I have and Arduino Uno and I  really would like to somehow control each set of each color as channels via PWM. I can't figure out how to power the sets of LED spots with the output of the arduino. I need an external power source and don't want to scrap all the wired LED's I bought. What I would like is to control each channel either through a manual control, or better yet have then light according to sound frequencies to slowly fade in and out along with ambient music. I've already posted this before, but I wasn't clear on the parameters I imposed on myself by needing to use the 12 V LEDs. Here are the specs for the blue ones:

High Brightness 5mm LEDs - 8000mcd
12V DC
Presoldered Resistor
20 mA
20 cm Wire Length
High Intensity - Low Power 0.36W

I need to figure this out by October and I know I have bitten off more than I can chew, but I really would love to be able to figure this problem out. I'm not looking for one of those light-o-rama style light shows, just simple fading in and out to help make the ambiance for my display. 

Thanks in advance for any help.
~GF
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Thank you, that makes a lot of sense. I appreciate the help.
Now I need to figure out how to input into the Arduino.
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So to I connect to both the Arduino GND and the 12 V DC power converter GND?
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Sorry, I found this answer.

Wire +12vdc to anode (positive) side of LED string, cathode side of led wires to collector, emitter wired to both negitive terminal of 12 volt voltage source and to arduino ground pin. Output pin to resistor, other end of resistor to base.
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So if I have it right, the 2N2222 can put out up to 800 milliamps so I should be able to power 40 parallel LED's on one channel? That's the maximum I would have on one channel. I plan to use 10-20 on three other channels (outputs).

I love learning, it is so empowering!
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OK, so two transistors coming out of the same output to two sets of lights.

Thank you!
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Sorry to be tedious, but I think this is the closest thing to what I want. Now I just have to figure it out.

http://railstars.com/hardware/led-intruder/
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The LED intruder can drive multiple channels of LEDs. From their website:
Uses only 5 input lines to individually control 16 LED channels.
"Daisy-chaining permits control of thousands of LEDs with no additional input lines.
Up to 20 LEDs can be assigned to each channel (using parallel-serial wiring), for a total LED count of 320 (although you must be careful not to exceed the maximum power rating of the board)"

Anyway, the local science electronic surplus amazing store The Reuseum has invited me to come in and get the project started.

http://www.facebook.com/pages/The-Reuseum/46622396060

Woot! I'm on my way.
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I haven't spent a dime on that project  (other than some LED's and the Arduino that I already had) and I have a very capable group of people to work with that want to help me succeed. So don't poo poo me!
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My 24-channel LED controller might work here. Only 20mA per channel, so you're looking at individual control: http://macetech.com/store/index.php?main_page=product_info&cPath=1&products_id=22

This might work too, you could put about 7 of the LEDs in parallel on each channel since they can run up to 150mA: http://macetech.com/store/index.php?main_page=product_info&products_id=10

Or find some other LEDs better suited to the task...the ones you have can't have been that expensive. If these are single LEDs wired for 12V operation, you are actually throwing away about 75% of the power you use.
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Unique RGB LED Modules and Arduino shields: http://www.macetech.com/store

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  I might have missed it but, was it ever determined if the spotlights were wired in series or parallel? Or could the spot lights be a combination of series and parallel circuits?

 It would make a big difference in what kind of current level you are looking at.

Mark
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You don't need to spend a dime to prove or disprove whether it will work for yourself. You can do it entirely on paper. Take the specs of your LEDs and the specs of the LED Intruder and see if it will handle the loads you proposed. Of course, you should do this kind of analysis before buying ANY product or component.

I think the LED Intruder is a great product. But it just doesn't appear to fit your original requirements. Or maybe you can change your requirements to fit the LED Intruder. Only you can make that kind of trade-off decision because you know the project and we don't.

My intent is not to "poo poo" you.  I am just suggesting that you do the calculations before getting excited about anything.

I think there is some ambiguity in the OP's requirements. If the intent is to run 10 LEDs off of one output channel, well, that's not gonna happen. That would fry the LED Intruder pretty quick (been there, done that). If the intent is simply to control LEDs in banks of 10, that's not a problem. The OP could wire one set of 10 LEDs to one LED Intruder, 1 per channel, using one LED Intruder per bank of 10. Using the formula on page 11 of the manual, 10 LEDs drawing 20mA @ 12V will consume 2750mW of power, well below the 3958mW hard limit. (16LEDs, however, is too many. Just FYI). This of course assumes that the OP has soldered the heat pad underneath the chip to the PCB. If the heat pad hasn't been soldered down, the hard limit will be a good bit less; if the OP breadboards with a DIP package, the hard limit is less yet, and 10 LEDs may be too much at 12V.

In which case, perhaps the OP ought to reconsider the 12V power supply, and go for something lower. A 5V supply would probably be just fine for this application.

Don (creator of the LED Intruder)
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