Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with led setup

  1. Aug 13, 2010 #1
    i recently bought a bunch of LED's from superbrightleds.com and wanted to replace the led's that are in my pc's case door. the LED's i ordered are the rl5-r1330.

    i wanted to know what other parts i would need to pick up from radioshack so that i dont burn them out. i dont know alot about LED's or how this whole setup works but i do know that the voltage that i saw for the specs superbright gives you said something like 1.9v. i know my pc molex power can put out 5v.

    i just wanted to know what i would need to get and how to set up the circut so that i don't fry my LED's. i also wanted to know how bright these lights will be or if i should consider getting different ones. in such case, what ones should i get.

    thanks so much for the help.

  2. jcsd
  3. Aug 13, 2010 #2


    User Avatar
    Science Advisor

    A really simple setup is to just put a 150 ohm resistor in series with each LED. LEDs usually have one wire longer than the other. This is the wire you would connect one end of the resistor to.

    Then you take the other end of the resistor to the 5 volt + supply (from the 4 pin molex plug. It will have a red wire going to it) and connect the other end of the LED to one of the center pins of the molex plug. These normally have black wires going to them.

    This will give a current of about 20 mA, which is probably OK for most LEDs. If you decide you want the LED dimmer, you can get a bigger resistor. They come in steps like this:
    100, 120, 150, 180, 220.....
    Reducing the size of this resistor would increase the current and increase the brightness, but you would have to know that the LED could handle extra current.

    A bright LED can get really annoying, though.
    Last edited: Aug 13, 2010
  4. Aug 13, 2010 #3
    the brightness wont matter much they are going behing frosted plastic on the front panel of my case.

    While im at it. will http://www.infomaya.net/v2/index.php?showtopic=59627" project work with these LED or am i gonna have to do something similar. to the above?
    Last edited by a moderator: Apr 25, 2017
  5. Aug 14, 2010 #4


    User Avatar
    Science Advisor

    That circuit uses 4 LEDs in series with a transistor and without any current limiting resistor.

    This is a risky idea because the transistor shown is capable of delivering a few amps and possibly blowing up the LEDs in one bright flash, if it is driven hard enough.

    If your LEDs are 1.9 volt types, and you use 4 of them, you could put a 220 ohm resistor in series with the LEDs and this would help to protect the LEDs.

    [PLAIN]http://dl.dropbox.com/u/4222062/led%20audio.PNG [Broken]
    Last edited by a moderator: May 4, 2017
  6. Aug 15, 2010 #5
    thats all fine and dandy but i have no clue what your diagram means. if you could, can you draw me up a diagram that a total idiot could follow. for both of these circuts. thanks a ton guys.

  7. Aug 15, 2010 #6


    User Avatar
    Science Advisor

    I have modified the diagram above to make it more like a picture.

    See if that makes more sense.
  8. Aug 15, 2010 #7
    yes, thank you, that makes a ton more sense. i can follow that. and as for the first circut, is it going to be similar to that picture as in where the resistor goes, or is it before EACH LED?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook