DIY led lighting

[randomperson21]

Heya all

So i just finished putting some custom etching on my plexi case window. looks pretty schweet.
Figured out that if you shine a focused beam of light, say from a led, into the side edge of the plexi, the light will travel down it and out the other end, much like fiber optics. and if the etched part is in the path, it glows! woo! pretty!

Now, heres the problem. Illuminating the damn things. I read a guide here showing how to make a 2 led diy light unit.
Essentially, its +7v----Led----led----gnd.
Tried this one out, looked ok, but it seemed to get hot.

Next, made it bigger
+12v---led---led---led---led---gnd.
Really cool, but really hot. stabalizes at 104F.

Now, i emailed this to my electronicly-inclined buddy (as you can most likely tell, i'm a total circut n00b), and he sorta freaked. Heres what he said:

Erm... Actually, you should be a little worried. LEDs are basically resistors, when forward-biased, and the law of resistors in parallel is that the more you have, the less the resistance, the more the current, etc. More than that, LEDs are also semiconductors, and across any PN junction the device is going to attempt to keep a .7v difference, and will pull current to get it. You need some current limiting. I would start with a 1k ohm resistor in series with each of the LEDs and see how the brightness is. I would mess with the resistance until you get a good glow, but nothing else. The circuit should look like this:

+12v ________ __/\/\/\___ LEDs_____
|__/\/\/\___ LEDs _____|
|__/\/\/\___ LEDs _____|
|__/\/\/\___ LEDs _____|
|__/\/\/\___ LEDs _____|
|__/\/\/\___ LEDs _____|___GND

You'll want to do this sooner rather than later... the 12v rail will be pulled low and do weird things with you computer, and, in the long term, cause your power supply to fail.

I don't understand any of this. If anyone here could help me get some diy led clusters up and running, it would be highly appreciated.

Or if anyone knows of a better solution for this??

i can post pics if you want.

 

[randomperson21]

thinking last night, maybe a 9v battery would work. less expensive to blow up than a psu.

 

[bbriand]

He has your LEDs in parallel (scratch that they are not in parallel - they are individual). The squiggly lines (_/\/\/\_) are the 1k ohm resistors. So you'll need one resistor for each LED.

There is a calculator out there that determines the size of the resistor depending on the current draw of the LED and the operating voltage of the LED. I'll try and find it.

[EDIT]
Note that he does NOT have the LEDs in parallel. They are individually powered.

I googled on "led resistor calculator" and came up with:
http://led.linear1.org/1led.wiz

Hopefully you have the electrical specifications of the LEDs you want to use.
[/EDIT]

Bill