store bought LED string...

[Omega]

i'm gonna go with the 330ohm way. i'm not trying to make sunshine inside the pc, just lighting it up a bit, so if dimmer is gonna give me longer life then thats good enough for me. Thanks to you too for making things clear

The path of higher resistance is safer anyways. Go with 330ohm. If they're too bright, step up the resistor to a 400 or a 500ohm resistor. If they're too dim, drop to 300 or 250ohms. Try not to drop too low, as if you give the LED too much current it'll go kaput.

Also, lifetime is a non-issue, as most LED's run for upwards of 20,000hrs at their designed specs. Now keep in mind there's 8,544 hours in a year and chances are you turn you computer off at least occassionally, so at normal specs that's 2+ years before replacing them.

Does the packaging or LED specs anywhere say it's mcd rating? That'll give you a good idea of it's brightness.

[xmastree]

Now keep in mind there's 8,544 hours in a year

I know that US gallons are smaller than proper ones, but I never knew your years are shorter too...

[crazybillybob]

I know that US gallons are smaller than proper ones, but I never knew your years are shorter too...

I'm in the US (mind you I do live in the woods, under a rock with snow on it!)
but here a year has at least 8760 hours in it. Years like this one have 8784 hours in them here in the back woods we call those leap years, they come round every 4 years, so they shouldn't effect your fancy math... Omega do you work for one of those investment banks or big insurance firms?

[blk03MitsuES]

i did use the 330 ohm and i can't tell a difference in lighting... so i soldered the resistor to the first led and cable then i went to test continuity and the little guy lighted up. so i went to solder the rest of the leds and cables. when i got done i went back to test it, and nothing happened so i pulled out a 9v battery and nothing. after a triple check of the + to - connections, i figured i was just gonna stick it into the molex connector to see what would happen. and sure enough the 6 leds lighted up

[crazybillybob]

Glad to hear that Everything worked out for you!

Now, LEDS are your friends, You'll be hooked, everything is going to glow around you!

This is not a bad thing ^



CrazyBillyBob

[Omega]

er, I can't math when I'm tired.

Still, it's between 8 and 9k hours.

[blk03MitsuES]

Glad to hear that Everything worked out for you!

Now, LEDS are your friends, You'll be hooked, everything is going to glow around you!

This is not a bad thing ^



CrazyBillyBob

actually everything used to glow since way back...

my pc room

http://www.youtube.com/watch?v=tXaAT4Aa2mk

my car

... but now i'm looking for a way to make the leds fade in and out lol already found a couple of tutorials using a 555timer and cap. but i got to find out how to make it work from 12v instead of 9v... just to get off the subject a little bit...
in essence, the 555 timer lets the cap discharge at specific time intervals based on the resistors on the pins... can i get away without using the 555 and simply use the capacitor to discharge randomly? btw this is what i was looking at http://www.geocities.com/SiliconValley/2072/proj2.htm the other i saw used the same things but had less explanations

[blk03MitsuES]

i'm at it again, this time with a 5v supply

First lets find the Resistor for 6 LEDS and see how that works. so supply is 12V Forward current is 20mA voltage drop is 1V, You have 12-6=6 So Ohm's law says R=E/I that means R=6/.02 or R=300 A 300 Ohm Resistor isn't common (Some thing the LED Calc takes into account) and most Resistors (at Radio shack) are 5% which mean they can be high or lower then rated be 5% so the 330 is a good choice.

so going back to the calculation i noticed something...

5v-5v drop(1v x 5 leds)=0????
R=E/I or R=0/.20
that just dont work out. but the led calculator suggested to use 1 ohm resistor for the 5 leds. the 5v supply is from the motherboards usb pins. so am i ok using 5 leds without a resistor? if i needed a resistor, how much difference would a 10ohm resistor due over the 1ohm? local radioshack only has 10ohm and no 1ohm... thanks again guys

[xmastree]

You always need a resistor with a LED.
What voltage are your LED's? 1V sounds too low, 1.5V is normal for Red. Higher for other colours.
If you're using six then I would use three strings of two.

In other words:

+5V --w-->|-->|-- 0V
+5V --w-->|-->|-- 0V
+5V --w-->|-->|-- 0V

[slaveofconvention]

You always need a resistor with a LED.

Erm, no. I have packs of 5v Blue LED's at home which I usually wire into PC's by wiring them direct to the Red/Ground cables from the PSU molex connectors - you DO always need a resistor for lower voltage LED's though...