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Okay, so here's what we know about your LEDs:
Forward Current - 20mA
Forward Voltage - 2.2
If you use a 9v power supply or battery and the LEDs are dropping 2.2v of that, then it means we need the resistor to drop 6.8v (9-2.2). We now know the voltage across the resistor and the current going through it (20ma or .02 amps, same as the LEDs), so we can use Ohm's law.
6.8v / .02A = 340 ohms
The next-highest standard value resistor is 390 ohms, so that's what you'd want to use (get 1/4 watt; 1/8 watt isn't big enough).
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BTW: technically you could power your 8 LEDs with fewer resistors, but this way you can have as few or as many LED/resistor pairs as you want without having to recalculate anything.
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You could buy a power supply from minispotlight, that way you aren't draining batteries. It seems to me they were like $15.00 or so. That just covers your source though, you still need them resistors.
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http://img80.imageshack.us/img80/3064/prototypeeu1.jpg
Ha! Who needs night classes when I have you guys, eh?
Now that I've created something that works, I can start on the real thing.
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By George, I think he's got it.
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O' Christmas tree, O' Christmas tree....
http://img88.imageshack.us/img88/5031/loc010jv4.jpg
Almost done with my prop.
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Nice work. I can't wait to see your prop.
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Thats awesome man it looks just like a real workbench with real tools! sweet prop!
