[computerfun]

my computer has a plexi glass side and a few blue led fans but i want it to be brighter, i bought a few 3000mcd blue leds from radio shack today and i was wondering how to wire them up in the case?

[computerfun]

can i just tap them into the fan wires?

[JohnWill]

LED's MUST have current limiting, so connecting them directly to a 5V or 12V source will quickly kill them. You should see a nice bright flash as they go. Typically, LED's require from 10 to 40 milliamps, depending on the specific device. They will also drop about .0.7-0.8V at full current. For a single LED connected to a 5V supply, that draws around 40MA, a 100 ohm 1/4W resistor would do the trick. You can also series them to minimize the amount of power disipated in the resister, but you should always have some resistence in series with LED's. You can't connect them in parallel, since the junctions are never have exactly the same voltage drop.

[computerfun]

right now i have a 3.7 volt led and i bought a 1.5k resistor for it, 1/2 watt, the led is 20ma.


can i just wire the resistor into the positive lead and then tap it off the fan or where do i get the power supply from?

[gotrootdude]

There's a few ways to get power to the LED's without adding a resistor. You could just tie into the power LED pins from the case header, or the HD LED for a flashing effect.

alternately, you can use a 47 ohm resistor and one of the USB headers on the board.

[computerfun]

that sounds good, exept im not a computer genius so im not sure what y ou mean by the case header, or the HD, but im sure if you explaned the component a little that i could locate it and get it goin, the flashing sounds cool i didint know it was capable to do that.

[kiwiguy]

You have a 1,500 ohm resistor and a 3.7vf LED.

If you select the 12v supply in the PC, you need to do the maths.

12v - 3.7v = 8.3 v which must be dropped across the resistor.

I (amps) = E (volts) / R (ohms)

So if you use the 1,500 ohm resistor, you will get a current of 8.3/1500 = .0055 (5.5 mA or a very dull LED, you need about 20 mA).

For 12v you need about 470 Ohms (nearest higher standard value), for 5v you need a 67 ohm resistor.

Using a value of resistor that is too low, or no resistor at all will mean that the LED will instantly be destroyed.

[computerfun]

ok so say i got a new resistor for it, where do i wire it in?

[computerfun]

i hooked my 1.5k resistor with my 3.7v led and hooked it to a 9Volt battery and it was very very bright, so the higher the number the less power it gets.

so 1.5k resistor would let less power to the led then a 470?

if thats true i wonder how bright it would be getting the proper amount of power

[JohnWill]

I = E/R, so yes, the smaller the resistor is, the more current that will flow, given a constant voltage.

[computerfun]

aright cool. so now how do i get these baby's glowin in my case, what do i hook the up to?

[JohnWill]

Originally Posted by computerfun

i hooked my 1.5k resistor with my 3.7v led and hooked it to a 9Volt battery and it was very very bright, so the higher the number the less power it gets.

so 1.5k resistor would let less power to the led then a 470?

if thats true i wonder how bright it would be getting the proper amount of power

Hard to say without knowing the specifications of the LED in question.

[JohnWill]

Originally Posted by computerfun

aright cool. so now how do i get these baby's glowin in my case, what do i hook the up to?

If you have a few LED's, you can connect them in series with a resistor to the 12V line. We need to know the exact number of LED's, as well as the current rating to give you specific details.

[computerfun]

i have one blue 3.7 - 4.5 max volt led, 20ma - 30 ma max,

[computerfun]

i could buy more of the same ones if it would make it easer to wire up?