Ordered 5MM Blue LED from CaseMod.com - came with NO instructions and NO connectors!!!

[KDOG]

I ordered this blue led from them and I need to find out how to hook it up. I thought for sure they would include some intstructions. They didn't :| Its 3.5V where in the heck do I hook that up at? Floppy power connector? I mean its 85 cents, so Its no big deal if I screwed up ordering it and can't use it. but I'm thinking about going to radio shack and getting a switch for my fans and the LED. Any ideas?

 

[ChefJoe]

It should hook up to your motherboard just fine. One of the wires should be longer than the other. I think the longer end is the negative end, but you should look up LEDs in the digikey.com on-line catalog to verify that. You'll need wires to connect it. You can hack up a cd audio cable to make a 2 pin cable or cut one already installed in your case or buy an LED tail. If you want to run your LED from the 5 v or 12 v rail, you'll need a resistor. There's on-line calculators for what resistor to get, but you basically need to know the voltage drop across the LED, the watts used by the LED, and the source voltage.

 

[amdskip]

Where are you going to mount it? Do you just want it one all the time or what?

 

[NinjaDriver]

Discrete LEDs usually have 1 lead longer than the other. The longer lead is the anode and you connect it to the + power lead. In a computer, you usually have 2 different DC voltage sources, 5 and 12V. Most LEDs like this are designed to run at .02 A or 20 mA. You've already stated that the LED is a 3.5V drop. I've already computed this out for you and if you use the 5V source, then you need a resistor that is 75 Ohms or greater. I think the closest thing you will find is 77 Ohms. You want the closest resistor to that value without GOING UNDER. If you connect it to 12V, you are going to need a 425 Ohm resistor. Once again, the closest value to that without GOING UNDER. If you go under, you will overpower the LED and cause it to burn out in a much shorter time. Back figuring the power draw of the resistors, you will need to find resistors that can handle 1/4 W of power. These are very easy to find and are cheap. You can find them at a radio shack near you...

BTW the 75 Ohm resistor only uses .03W and the 425 Ohm resistor uses .17W....well under the .25W handling capacity of these tiny resistors.