# Thread: LED's and Resistors Guide

1. ## Re: LED's and Resistors Guide

Originally Posted by calumc
I wouldnt worry at all about that, it would come into play only if you had a large amount of leds. If I was doing it I'd just wire them all up to a 47ohm resistor on the 5v line
Would that work on a 5v line? 3.0+3.0+2.6+2.6=11.2V

Now I realize that just wouldn't work in series, and that it probably would if I just hooked them up in parallel, but then I'm sticking resistors on each LED.

I just want to make sure I'm doing my math right mainly, like I said, because I'm way out of practice.

2. ## Re: LED's and Resistors Guide

A quick diagram for you:

3. ## Re: LED's and Resistors Guide

Originally Posted by calumc
A quick diagram for you:
BAH! I can't see it from work, damn Army network, so I'll check it out when I get home. Thanks!

*scribble scribble* Yea... Gotta make sure I stop and get my resistor on the way home.

4. ## Re: LED's and Resistors Guide

Originally Posted by Nameless
Edit: After thinking about this, since two of my LEDs require different current I think I need to run my Red LED's in Series and my Yellow LED's in Series, and then run the two different colors in Parallel to the 12V power source, since I don't think 5V or 7V can push this. Is that right?
That's what I would do.

As for the equation, for the red ones:

2x Red LED's @ 2.6VDC/28mA

So the total volt drop across the LED's is 5.2V, leaving 6.8V (12 - 5.2) across the resistor.
R=V/I so 6.8/.028 = 242.

So 240 ohms is the nearest one there.

2x Yellow LED's @ 3.0VDC/20mA

6V/.02A = 300 ohms

Don't try calumc's suggestion. Sorry, but putting LED's of different voltages in parallel will never work. The red ones will clamp the voltage to 2.6V, so the yellow ones won't conduct at all.

5. ## Re: LED's and Resistors Guide

Originally Posted by Nameless
BAH! I can't see it from work, damn Army network, so I'll check it out when I get home. Thanks!

*scribble scribble* Yea... Gotta make sure I stop and get my resistor on the way home.
Quick word of advice for you.. don't buy Radio Shack stuff. Nothing but crap from them. Check out www.lsdiodes.com. Great stuff.

6. ## Re: LED's and Resistors Guide

Originally Posted by xmastree
That's what I would do.

As for the equation, for the red ones:

2x Red LED's @ 2.6VDC/28mA

So the total volt drop across the LED's is 5.2V, leaving 6.8V (12 - 5.2) across the resistor.
R=V/I so 6.8/.028 = 242.

So 240 ohms is the nearest one there.

2x Yellow LED's @ 3.0VDC/20mA

6V/.02A = 300 ohms

Don't try calumc's suggestion. Sorry, but putting LED's of different voltages in parallel will never work. The red ones will clamp the voltage to 2.6V, so the yellow ones won't conduct at all.
Much thanks! That's what I was thinking, but it never hurts to ask just to be sure.

7. ## Re: LED's and Resistors Guide

Originally Posted by SgtM
Quick word of advice for you.. don't buy Radio Shack stuff. Nothing but crap from them. Check out www.lsdiodes.com. Great stuff.
Nice site. Any reason Radio Shack LEDs are crap in particular? I already got the ones I'm using in this project from there, but I'm sure I can use the site you posted in the future because they seem pretty sharp.

I was just wondering if you had some experience you'd like to relay about Radio Shack LEDs or stuff in general, as it sounds like you've had a bad experience or two.

8. ## Re: LED's and Resistors Guide

Just more expensive for the same thing. \$4 for 1 LED vs .45 for 1 LED and freebies. I'll order from lsdiodes any day of the week.

9. ## Re: LED's and Resistors Guide

Originally Posted by SgtM
Just more expensive for the same thing. \$4 for 1 LED vs .45 for 1 LED and freebies. I'll order from lsdiodes any day of the week.
Ditto! I have an order in with them right now!

10. ## Re: LED's and Resistors Guide

Originally Posted by SgtM
Radio Shack stuff. Nothing but crap from them.
Originally Posted by Nameless
Any reason Radio Shack LEDs are crap in particular?
Originally Posted by SgtM
Just more expensive for the same thing.
So not really crap then, just over priced?

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