Project L-E-D
The cheapest case-mod you ever saw!

Product: LEDs & Pizza
Manufacturer: Guru3D.com ;)
Author: Brann Mitchell
Date: October, 2002

File Under, You Can -- But Should You?

I started thinking about using LED's as a light source in my case quite a while ago.  LED's have a lot of advantages over cold cathodes for case lights, starting with less clutter, less heat, and easy to power.  I didn't even want to cut up the beautiful aluminum of my case for switches or fans, either.  No, I wanted to do something different, something that didn't take up a molex power connector, and had more of a chance that I could burn down the house.  And be cheap, too.  I decided to make a LED case light powered by your trusty USB.  It's really a lot simpler than it looks, but there are few details that need some attention.

Since you'll need some tools that do have potential to burn down the house, cut fingers off, or at the least put an eye out, I guess I need to put in a disclaimer.  Should you follow this as a guide, do let me stress, we at guru3d.com aren't responsible if you hurt yourself, your computer, or anyone in your general vicinity, including your cat.  I'll try to put in some safety tips here and there, where appropriate.  Start with putting the cat out.  Good preparation is a great way to avoid unnecessary injury.

You'll need a few parts and tools, LED's and resistors mostly, a few USB cables, an internal-to-external USB adaptor, and some tape.  For the tools you are going to need a soldering iron, solder, wire cutters, a voltmeter (optional, but very handy), and safety glasses (I'm not kidding!).  Also look for a decent place to work, something that won't burn too easily, like a bathroom with ceramic tile.

The USB adaptor is normally supplied with your motherboard, so you should use that.  Motherboard manufacturers like to have their own pinouts for the USB headers, so if you need to get one, make sure it's compatible with your mobo.  Check the links at the bottom for the page with the common pin outs.  I had three available, one for my Asus mobo, one left over from an Abit mobo (now deceased), and one I picked up at a flea market.

Asus, no-name, Abit, from left to right. I used the one in the middle, the no-name.

Two USB ports in one connector.

The Truth is Straight Ahead

Oh, yeah, you'll also have to remember Ohms Law: y(t) = k₁ e^s₁ ^t + k₂ e^s₂ ^t

No, I'm kidding.

Ohm's Law: Voltage (V) = Current (I) * Resistance (R)

V=I*R

Yep, math.  I think I just felt half of the audience go cross-eyed.  And the other half raised their hands to be excused to the bathroom.

What kind of LED you choose will determine what value of resistor you'll need, measured in Ohms.  This is because LED's operate at a different voltage than USB.  Luckily it's a lower one, so we can use a resistor to drop the voltage.  I'll get to the math as I build the light.  You'll see.