LEDs and resistors

[garwain]

How do you calculate the what you need for resistors? Please correct me if I'm wrong, my leds are 2.1V, so if I put them in series that would be a total of 4.2V max, so if I'm going to put them on a regular 12V line, I'll need resistors to remove 7.8V, right?

Now, how do I figure it out from there? My courses on electronics were a long time ago, and I'm now wishing I'd paid more attention
:eek:

[CJ145]

Here you go. http://hw.metku.net/index.html?sect=view&n=1&path=mods/sahkooppi/index_eng

[KeyboardCowboy]

the good duded at you local radio shack should also be able to help you, tell you what you need, ect


that is what i did when i did my switch/led mod

[garwain]

1st of all, thanks cjreis that link will be very helpful

2nd, the guy at Radio Shack was the first person I asked and he scribbled down a few numbers then handed me a packet of resistors, telling me "a few of these should be about right". Not all that helpful. I'd rather work it out myself, solder everything together, then pull out the trusty old multimeter to test it, and light up

[Arkaine23]

I think I used a 680 Ohm resistor for the 12v line to power a 5v led. Silly, eh?

[CJ145]

I used it to do this. http://forum.oc-forums.com/vb/showthread.php?s=&threadid=102800 The pictures are at the bottom and are really blurey but it looks aswome.

[NTX-Zoner]

I think you could pass those pics off as modern art
:beer: :p :beer:

[Mpegger]

LED 101 (http://misty.com/people/don//ledd.html) For the virgin LED modders out there.:D

[Shaotai]

Okay, so I replaced my power and HDD led on the front of my case with some Radio Shack 5mm blue LEDs. The hdd one works just fine. Looks good too. When I changed the green led for the power to the blue, nothing happens. It's plugged in the right way, and the led works in the hdd plug, so I know it's not a problem with the led. From looking at the the sites that were refered to, blue led use higher voltages. So I bought a 4v blue led and it barely lights up, but is still too dim. Could it be that the motherboards don't supply enough voltage/current to light the blue leds up?? My mb is listed in the sig...

[Mpegger]

Originally posted by Shaotai
So I bought a 4v blue led and it barely lights up, but is still too dim. Could it be that the motherboards don't supply enough voltage/current to light the blue leds up?? My mb is listed in the sig... Simple answer, yes.

The average LED falls in the 1.2-2.5 voltage range since thier normally low MCD, wide angle diffuse LEDs. However, theres usually a surface mount resistor in series with the LED in order to bring the voltage and milliamp into the proper range for the LED in use. If you follow the trace on the board and can check with a multimeter if the smt you run into is in fact a resistor, you can probably desolder and remove it, solder the contacts together, then use your own resistor at the point where the LED normally is. Hopefully the voltage and mA supplied by the board without the resistor will be enough for a highpower LED.

[CJ145]

My blue Led's are 3.7 volts.

[Shaotai]

Where did you get those LEDs?
I'm thinking of just wiring it straight to a 5v line.. do I still need a resistor to do that?

[CJ145]

The led's were bought from radio shack. The blue's are wired in parelell each has a 68ohm resistor to run them of a 5v line. When you use a resistor you use the one that is nearest to the resistance needed the blue was 65 and the closeist resistor was a 68ohm.

Edit: I know now what my dad learned in coledge from the site above and I'm 13.