RGB led white light

Discussion in 'General Electronics Chat' started by adamclark, Oct 6, 2013.

  1. adamclark

    Thread Starter Member

    Oct 4, 2013
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    hello,, I recently tore apart an old scanner for the light strip that runs across it. Normally from all instructables ive read, its supposed to be a bulb. But this one had a RGB led with a clear rod to make the bright white light.. it has one positive leg and each of the other 3 make different colors when ground is applied to them. Now I figured since it only has one positive leg that putting the ground to the other three would light all three colors up making the light white... WRONG....... it simply turns red...What should I do to get the white light im looking for? I want to build a desk lamp for my work bench out of it.. It will look very
    electro-mech/industrial ... thanks
     
  2. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    I should also mention that I want to use separate switches to be able to light the red, blue ,green and white individually.. I also have a handful of 555 timers that I have been learning with. Could I use a 555 to control the colors separately? and maybe add some other functions like oscillating colors? Or maybe one switch with the 555 to control all functions?
     
  3. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    ok,, so Ive noticed by adding resistors to the legs I can dim the colors, but I still cant make white.. does anybody at least know the combination to get white light from a RGB led?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,545
    2,370
    Normally an equal intensity of RGB results in White.
    Max.
     
  5. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    that's what I thought too,,from what ive read in other posts red and green should make yellow,, all three should make white, and green and blue should make turquoise,, well the red overpowers all of them.. straight red and green make red,, all three make red, green and blue make turquoise,, now if I put a 1k resistor ont the red and add green it starts to yellow.. all three with the 1k on the red makes a real light turquoise.. so I think im getting closer to white... I have some regular rgb leds I bought in a radio shack led kit and they make white, but this one I scavenged from the scanner is really high intensity.. when the scanner was working it was super bright.. so I want to use this one for my desk lamp, as Im not sure a regular rgb would be bright enough..
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    you need to use a constant current supply on each of the cathodes, and alter each one separately to obtain the correct colour/hue of white..
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,798
    1,103
    The R is clearly dominant, so needs less current than the G and the B.
     
  8. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    i did a search on the forums here and seen a few of you talking about using 555 timers with PWM to control the colors.. I have about a dozen of the 555's (im new to electronics and thought the 555 timers and a bunch of leds was a good starting point). So would this be a good idea and if it is where would I start? I can read a schematic and ive assembled several projects already, But I need a remedial explanation to understand things. I cant really learn from theory or explanation, I need to do things hands-on to actually learn it..
     
  9. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
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    Turn B and G full on, turn R up enough to get near W, then adjust G or B down to get W. If you do this with pots, measure the resultant resistance and replace with fixed resistors, then you can operate from a well-regulated constant voltage.
     
    Last edited: Oct 7, 2013
  10. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    OK,, so I put a 0-6K pot on each lead and im able to "tune" it in to whatever color I want... So with that figured out its on to the next part.. I don't want to use the pots as they are now, so its on to the 555 PWM idea.. I have started a thread in the projects board so please post any ideas or help with that in that thread.. Thank you very much for helping me learn..
     
  11. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    I have figured out the problem this thread was for. I have started another thread in the projects board for the next part of my project, So could you please close this thread so I can keep all of the posts for my project in one place.. Thank You
     
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