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SOLVED Need help wiring LED

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HeatM1ser2k4

HeatM1ser2k4

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Joined
Oct 6, 2004
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I have these LED lights and I would like to wire one of them so that it can plug into my motherboard and light up whenever the computer is turned on.How would I do this properly?

I took a wire that was on an old motherboard and connected the LED to it, then plugged it in, but it didnt work. The wire had 2 female adapters...meaning it looks like a wire that would plug into the SPDIF part of the motherboard. I plugged it in and it didnt light up, but I wiggled it a little and burned the LED out, so I'm wondering if I didnt ground it correctly or something. This is probably very simple, but I dont want to fry my equipment while experimenting, so any assistance I can get would be greatly appreciated.
 
Meaning one wire from the led needs to connect to a positive terminal and the other to a negative terminal?
 
Yeah. Diodes allow basically infinite current in one direction (forward biased) and zero* current in the opposite direction (forward biased).

Typically the longer leg of the LED is the positive leg. If it's a different type of LED, look up the data sheet so you don't fry it.

* This is up until the breakdown voltage.
 
Last edited:
Yes, one leg is positive and one leg is negative.

Also, make sure what voltage you're giving it. If its rated for 5V and you give 12V, you'll let the magic smoke out.
 
Yupp. ^^^ He's right. I was going to add an edit, but it never got saved.

It's not a bad idea to throw a 10k Ohm resistor on the ground side of the LED just to start. If it's really dim, then you can change to a smaller resistor, but 10k is usually a good place to start.
 
ok...I'll pick a 10k Ohm resistor up and try it that way....maybe I was plugging it in to too much current...I'll post back my results in a day or two when I can work on it again...thank you!
 
Without a current limiting resistor an LED will die quickly. That's almost certainly what happened. Actually, that is what happened.
As for turning on when the computer turns on, you can wire it to a Molex or FDD power plug and get the same effect, without having to muck with your motherboard.
 
Bobnova said:
Without a current limiting resistor an LED will die quickly. That's almost certainly what happened. Actually, that is what happened.
As for turning on when the computer turns on, you can wire it to a Molex or FDD power plug and get the same effect, without having to muck with your motherboard.
Click to expand...

Wow...that sounds so much more simple. I should be able to do that tomorrow. I have a few molex-to-SATA adapters. If I used one of those and left it unplugged on the SATA adapter end, would that also work?
 
Yeah. A Molex to SATA plug with the SATA cut off is a great way to go. That gives you 12V and 5V. I'd use 5V for the LED, and a 1kOhm resistor to kick things off. That'll work for pretty much any LED at 5V. You can use a lower resistance for more current flow and a brighter LED assuming the LED can handle it.
The red wire is 5V, blacks are ground, yellow is 12V.
 
Let me just make make sure that you didnt have a typo(since someone said 10k Ohm earlier)... I would need a 1k Ohm resistor or a 10K Ohm?
 
HeatM1ser2k4 said:
Let me just make make sure that you didnt have a typo(since someone said 10k Ohm earlier)... I would need a 1k Ohm resistor or a 10K Ohm?
Click to expand...

1KOhm would be fine. Your standard little 5mm/3mm LED can take about 20mA. Hooking it up to 5V in series with a 1K ohm resistor would give you less than 5mA, exact current depends on the voltage drop across the LED, so you're well within the safety margin.
 
Last edited:
1k for 5V rail. For 12V rail, 10k is safer in case of very low power LEDs.
 
I have the resistors. Firstly, are these the right ones to use?

Secondly, do I need to know what the colored rings mean? And finally, do I add one to the positive and negative wires, or just the positive?
 
New to the forum... But thought I could help on this one...

That 1K resistor will be fine. It will result in a current of about 3mA through the LED, which might be a bit dim, but certainly it should not harm the LED. If it's too dim, follow along the rest of this, and you can choose a new resistor value that will likely be brighter. The colored rings of the resistor, tell you the value of the resistance, and the tolerance for the resistor. Here's an online calculator for decoding the bands, if you are interested:

http://www.digikey.com/us/en/mkt/calculators/4-band-resistors.html

Note that it does not matter which end of the resistor you connect to the LED. Resistors are not directional.

LED's are directional. Here's a nice online calculator that will calculate a resistance to use. You'll need to know the forward voltage of the LED (Voltage drop across LED), the Supply Voltage (Either 12V or 5V for your case), and the desired LED current. The calculator also gives a nice diagram of how to wire the LED. Note that using a higher value resistance for the LED, will reduce the current, which will always be safe for the LED. So when choosing a resistance value, use the calculator, and then choose a resistor the same value or higher in resistance.

http://www.quickar.com/bestledcalc.php?session=

It is best to get what the LED can handle from the datasheet for the LED, but the following are some general guidelines:

Rule of thumb values to use for calculations with unknown LED's
20mA for all colors
Blue, White, Green, Pink, Purple, 3.3V voltage drop.
Yellow, Red, Orange, 2.0V voltage drop.

Here's a great online article regarding LED's, and powering them. It covers them in a pretty basic manner.

http://www.quickar.com/ledbasics.htm

Hope that helps!
 
If it is : (standard leds without other built in "stuff")
White or blue: it needs about 3.5V
Red or Yellow: it needs about 2.1V
Green is in the middle: about 2.5V

You can use the 3.3V line (orange wire) and power a white or blue directly...
 
circuitwizardry said:
New to the forum... But thought I could help on this one...

That 1K resistor will be fine. It will result in a current of about 3mA through the LED, which might be a bit dim, but certainly it should not harm the LED. If it's too dim, follow along the rest of this, and you can choose a new resistor value that will likely be brighter. The colored rings of the resistor, tell you the value of the resistance, and the tolerance for the resistor. Here's an online calculator for decoding the bands, if you are interested:

http://www.digikey.com/us/en/mkt/calculators/4-band-resistors.html

Note that it does not matter which end of the resistor you connect to the LED. Resistors are not directional.

LED's are directional. Here's a nice online calculator that will calculate a resistance to use. You'll need to know the forward voltage of the LED (Voltage drop across LED), the Supply Voltage (Either 12V or 5V for your case), and the desired LED current. The calculator also gives a nice diagram of how to wire the LED. Note that using a higher value resistance for the LED, will reduce the current, which will always be safe for the LED. So when choosing a resistance value, use the calculator, and then choose a resistor the same value or higher in resistance.

http://www.quickar.com/bestledcalc.php?session=

It is best to get what the LED can handle from the datasheet for the LED, but the following are some general guidelines:

Rule of thumb values to use for calculations with unknown LED's
20mA for all colors
Blue, White, Green, Pink, Purple, 3.3V voltage drop.
Yellow, Red, Orange, 2.0V voltage drop.

Here's a great online article regarding LED's, and powering them. It covers them in a pretty basic manner.

http://www.quickar.com/ledbasics.htm

Hope that helps!
Click to expand...

That info is very very helpful...thanks for all the assistance! Now that I'm a pro electrician, I'm going to rewire the house!
 
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