# LED's in computer case



## computerfun (Nov 12, 2006)

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?


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## computerfun (Nov 12, 2006)

can i just tap them into the fan wires?


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## JohnWill (Oct 19, 2002)

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.


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## computerfun (Nov 12, 2006)

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?


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## gotrootdude (Feb 19, 2003)

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.


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## computerfun (Nov 12, 2006)

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.


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## kiwiguy (Aug 17, 2003)

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.


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## computerfun (Nov 12, 2006)

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


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## computerfun (Nov 12, 2006)

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


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## JohnWill (Oct 19, 2002)

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


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## computerfun (Nov 12, 2006)

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


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## JohnWill (Oct 19, 2002)

computerfun said:


> 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.


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## JohnWill (Oct 19, 2002)

computerfun said:


> 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.


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## computerfun (Nov 12, 2006)

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


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## computerfun (Nov 12, 2006)

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


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## JohnWill (Oct 19, 2002)

I'd say around 400-450 ohms would be good for that LED if you're connecting to +12V. 400 ohms will drop 8 volts at 20 ma. If you want it a little brighter, you can go as low as 270 ohms for 30 ma across the diode.


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## computerfun (Nov 12, 2006)

aright sweet, so now how do i wire them in the computer safely?


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## JohnWill (Oct 19, 2002)

Well, I'd suggest heat shrink tubing for covering the resistor and it's bare soldered connections. You obviously have to make sure the 12V doesn't short to the case.


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## computerfun (Nov 12, 2006)

ok, sounds good.

now where do i find the 12 v power supply, and can i tap into it or is there a fan outlet i could tap off of?

how do i go about actualy putting it in?


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## JohnWill (Oct 19, 2002)

The 12V P/S is everywhere. The black and yellow leads to the disk connectors are 12V, and you can get an adapter intended for a fan to connect to one of those and solder your connections to the end of that.


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## computerfun (Nov 12, 2006)

do i have to use an adapter?

is it going to be safe to tap into the powersupply ( its not going to raise or drop the ohm load or create a problem )

so everywire that is red or yellow is my power supply, red + yellow -


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## computerfun (Nov 12, 2006)

could i maybe just make it really simple and tap off the fan power supply or is that 5v, and would it disturb the fans function?

im just nervous cuz i do alot of car audio and i know that in car audio anything you connect is going to effect something somewhere else, im not a computer genius like i am car audio. and i spent about 600 bucks for my sissters boy friend to build this PC for me but they broke up so i have no help on these lights.


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## JohnWill (Oct 19, 2002)

I would not tap into the fan connection. First off, most of them are not +5, but also +12. Also, most of the fan connections have very limited current capability, and many fans are also speed controlled by varying the voltage.

If you connect the negative leg to the black connection, and the positive leg to the yellow connection of a disk drive connector, you can run all the LED's you can stuff in the case without affecting the operation of the computer. You can easily draw 3-4 amps from that connection, which is enough for several hundred of those LED's.


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## computerfun (Nov 12, 2006)

sweet, so do i have to wire them a certain way to keep the prober impedence, or can i just wire them all in series?


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## JohnWill (Oct 19, 2002)

If you wire multiple LED's in series, you need to consider the voltage drops of them all in selecting the resistor. I thought you said you had one?


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


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## computerfun (Nov 12, 2006)

i do have one, but now that you said i can stuff as many as i want, since there so cheap then why not


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## JohnWill (Oct 19, 2002)

If they really drop 3.7V, you can put two in series with a resistor in the 150-200 ohm range across the +12V. What is the exact part number of the LED you have?


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