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Help with a simple circuit.

Discussion in 'General Electronics Discussion' started by oneslowz28, Dec 29, 2008.

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  1. oneslowz28


    Dec 29, 2008
    I am working on a custom computer case for my buddy as a surprise gift for when he returns home from Iraq. He is a big gamer and I have been building him a gaming computer over the last few months. I am almost finished with the case and now need a way to control the fans. Instead of buying an off the shelf and over priced rheobus I decided to build one that would fit my needs. The simple circuit for the voltage control using a lm317t, 300 ohm resistor, 240 ohm resistor and a 2.2k trim pot was easy.

    What I am having a problem with is figuring out how to make an RGB led light up a different color at a supplied voltage. IE: red at 3 volts, blue at 7 volts and green at 12 volts. Can anyone help me with the circuit design? I am going to build this on perf board so no need to generate any pcb designs in eagle or anything. A simple schematic will suffice.

    Thanks in advance.
  2. Resqueline


    Jul 31, 2009
    Some lucky friend you got!
    You might get some ideas by looking at or or or even if you are a PIC buff.
    I'd suggest using 6, 8, & 10V intervals as few fans turn over before 5V and not all regulators give more than 11V.
  3. neon


    Oct 21, 2006
    no biggy red leds are usualy 2v so need a 3v need 50 ohm in usualy run 4v so need a 150 ohms in series with that. green maybe 3v i assume so needs 12v and a 450 ohms in series
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