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Installing a Blue Power LED
By Bones (Ed T. Toton III)
October 11, 2002

Blue Power LED In our previous article "Connecting LEDs to your Power Supply", we discussed the math behind choosing a resistor to properly connect LEDs to power without burning them out. But how about something more practical? It turns out that replacing the power LED in your computer case may be even more simple than you realized.

As you may know, a standard molex power-connector from your power supply contains 4 wires: +12v, +5v, and two grounds. Additionally, most computer cases simply use standard 5mm LEDs that snap into place in the bezel or faceplate. If you're interested in using a blue LED for your power-light, Radio Shack happens to sell one that makes the task insanely easy. Radio Shack part #276-311 is a blue LED of moderate brightness that happens to have a forward voltage of +5v.

As we discussed in the Connecting LEDs how-to, we know that:

Rs = (Vin - Vled) / Iled

In this case, the required resistor for use with the blue LED would be:

Rs = (5 - 5) / 0.03


Rs = 0 / 0.03 = 0

Since the voltage requirement and supplied voltage cancel out, no limiting resistor is required, and we can connect the LED directly to the +5v line (the red one... the +12v line is typically orange or yellow).

Blue Power LED All you need to do is find a standard floppy-drive power adapter, and stick the LED leads right into the pin-holes on the connector. They actually friction-fit very nicely, and all you need to do is make sure you put LED on the right way (it won't light up if you get it backwards). The longer lead is usully the + (positive) side. Then with a little electrical tape (see the picture on the right), it can be kept safe from shorting against other objects. Then simply use a pair of needle-nose pliers to remove the old LED, and then stick the new on in it's place. This power LED will not be powered from the motherboard (which usually won't work with blue LEDs due to their higher voltage requirements), but since the drive-connectors from your PSU (power supply unit) are only active while the system is on, it will work correctly as a power light on your computer.

Once everything's in place, power up your system and enjoy the nice new blue glow!

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