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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

    oneslowz28

    1
    0
    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

    Resqueline

    2,848
    2
    Jul 31, 2009
    Some lucky friend you got!
    You might get some ideas by looking at .discovercircuits.com/DJ-Circuits/voltst1.htm or schematics.dapj.com/2005/07/voltage-level-indicator.html or .national.com/mpf/LM/LM3914.html or even .edn.com/article/CA484496.html 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

    neon

    1,325
    0
    Oct 21, 2006
    no biggy red leds are usualy 2v so need a 3v need 50 ohm in series.blue 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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