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 Post subject: MOD Idea, Need A bit of help figureing out how to go about..
PostPosted: Tue Mar 01, 2005 11:20 am 
8086
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I have an Idea for a mod, How would i connect several LEDs, like 10 for instance to one of the connectors of the PSU? preferrable one of the AUX connectors, i dont think i will need resistors if i put enough LEDs to even out the load. i plan on doin this till i can get a cathode, ithink it is a good alternative since i got sum LEDs lyin around..

heres a crappy paint drawin of wut i wanna do, i do need some help findin out where to put the wires etc, like an instruction of how to connect it up to the PSU connector

Image


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 Post subject:
PostPosted: Tue Mar 01, 2005 12:39 pm 
Little Foot
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The low-down on LEDs: http://led.linear1.org

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 Post subject:
PostPosted: Tue Mar 01, 2005 1:05 pm 
8086
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lol the LED arent the problem its just where to connect the wires im usin to the PSU cable

like where is the + end and where is the - end. I know the red wire is 5v and the yellow is 12v though.


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PostPosted: Tue Mar 01, 2005 1:54 pm 
Clawhammer
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Black = Neg.


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 Post subject:
PostPosted: Tue Mar 01, 2005 2:59 pm 
8086
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which wires would b the red yelloow and 2 blackones that would b on a regular 4pin molex except where would they b on the main board connectior or the atx psu


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 Post subject:
PostPosted: Tue Mar 01, 2005 6:49 pm 
Boy in Black
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Image
That is if you're looking at the board, and that box is the key. The one left out is where a yellow wire will go, but it's only for the speed sensor and not the same as the yellow wire on the molex. Only the Red and Black can be used to power anything from the board.

And your actual wiring will need to be something like this IMO:
Image
I left out the R on the + lead, but those are hard to draw:p Put a squiggle on the red lead going up to the LED.

So, I'd rather have resistors on each one with the positive lead just making dumps at each one. That's so easy to make compared to one big series string. In your drawing, there is not positve and negative, so they'll never foward bias. Anyway, when you put this in a case this will be easy to do. I'm thinking you should ungroup them and place them in different spots. Like, 2 here, 3 there, 1 here, 1 here...

Also remember that an LED is a Diode. It will need to be wired in only one direction, and you'll need to get 5v to power the string up. This means that you will need resistors to get the entire string down to 5v from the 12v supplied at the plug, with the MAX voltage usually being 6v. I think the magic resistor to use would be one 560-ohm for one LED. The Radio Shack P/N would be 271-1116 (5% tolerance units). And the Radio Shack P/N for 5mm Blue Led's would be 276-311 if that's of any interest.

The wizard reports back 270 ohm, so I may be looking at the wrong pack of resistors. I'll have to dig up my old project and double check this resistor. However, the wizard also said my LED fowarad supply voltage of 5v was suspeciously high...it's not :p


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 Post subject:
PostPosted: Tue Mar 01, 2005 7:35 pm 
8086
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First post here, so hi everybody....

Maybe I can help clarify some of the answers given already.

dsforsaken wrote:
i do need some help findin out where to put the wires etc, like an instruction of how to connect it up to the PSU connector

http://led.linear1.org/led.wiz is intended to help you with the first half of that, the second you've gotten some good advice on already.

dsforsaken wrote:
i dont think i will need resistors if i put enough LEDs to even out the load.

That is a possible configuration--I find most people don't like to take the hit in brightness from doing it that way though. For example, take 4 blue LEDs in series--each has a rated forward voltage of 3.3V @ 20 mA. If you connect them in series across 12V (the yellow and black wire from a PSU molex), you'll get them to light, and draw around 11 mA (depends somewhat on the diodes, this was what I found when I tried it myself). But operating 3 in series at 20 mA with a 120 ohm resistor was brighter.

Resistors give you more control over the operating current than no resistors. So in general I recommend them.

dsforsaken wrote:
like where is the + end and where is the - end. I know the red wire is 5v and the yellow is 12v though.

Like Chumly points out above, a diode will only light when wired up in one direction. The longer lead is the anode, or positive side of the LED.

Resistors don't have polarity at all, they can be inserted anywhere in the circuit and have the same effect.

Chumly wrote:
It will need to be wired in only one direction, and you'll need to get 5v to power the string up. This means that you will need resistors to get the entire string down to 5v from the 12v supplied at the plug, with the MAX voltage usually being 6v.


Without seeing particular specs of the LEDs dsforsaken has, we're just guessing, but diodes have a rating that looks like
Quote:
3.3V @ 20mA
in other words some voltage at some current. That rating isn't the minimum, or turn-on voltage, it's a typical operating point.

20mA is a typical value you see in current ratings for 5mm LEDs, but the forward voltage will vary widely by what the material the LED is made of. It can range from as low as 1.5V for infrared up to 4.6V for some types of blue LEDs (most common blue ones are more like the 3.3V @ 20mA I used as an example above).

So like I said, it takes some knowledge of the specs to use the LED wizard, but we can do an example without them:

Let's say dsforsaken has two dozen red LEDs, 2.0V @ 20mA.

The values to enter into the wizard are
12 Source voltage
2.0 diode forward voltage
20 diode forward current (mA)
24 number of LEDs in your array
Which gives this result (click to see the solution)

You could very likely omit the 1 ohm resistors shown there. But they're cheap insurance.

Chumly wrote:
However, the wizard also said my LED fowarad supply voltage of 5v was suspeciously high...it's not :p

To be clear, the wizard would have warned you if you entered 5V as the diode forward voltage (not the supply), because it is not typical of LEDs. You can buy LEDs with internal resistors that carry that rating. That's why the wizard does the calculation anyway after issuing a warning.

The wizard outputs a wiring diagram that shows four parallel strings of six LEDs in series with a one ohm resistor. The picture of the LED has a flat edge on one side of the case--that corresponds to the actual LED case, which will have a flat edge marking its negative (cathode) leg.

dsforsaken, that may be more help than you wanted, but I did want to clarify how the LED wizard helps out if you have questions like this. I hope you guys find it useful, thanks for giving it a try.


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