RGB LED variable colour and strobe current colour (without PIC or Arduino)

Discussion in 'The Projects Forum' started by tioJim, Dec 7, 2014.

  1. tioJim

    Thread Starter New Member

    Nov 12, 2014
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    Hello

    Limited electronics knowledge, forewarned! :) Although I do have some ...

    I want to be able to control an RGB LED such that a full range of colours are available

    Is the following basic theory correct for obtaining range of colours, use PWM to vary brightness of each colour channel R, G and B independently?

    I have already built a simple 555 based circuit for strobing and varying a single colour LED. So just this circuit times three?! Is there a clever way of doing three channel PWM with a single 555?

    What if I then wanted to strobe the current colour? Again can it be done with manipulation of the existing PWM controller or would I need a separate strobe circuit?

    How about, then cycling through a range of colours? Getting complicated ...

    I'm thinking I don't want to use a PIC or Arduino or other micro controller to keep things simple, but perhaps a micro controller is the simplest way? I have built very bare bones Arduinos and I guess the component count is pretty low although the chip has quite a large footprint.

    I realise the circuit and theory is potentially quite complex so just pointers for further research would be very helpful. I'm not expecting anyone to hand it on a plate to me!

    Thanks
    Jim
     
  2. tioJim

    Thread Starter New Member

    Nov 12, 2014
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    Ooh, also I don't want to use an off the shelf solution as I'd like to take the opportunity to learn and increase my understanding of electronics.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    There are two ways to control the intensity of a single LED:

    1) by controlling the current through the LED,
    2) by PWM.

    Yes, simply multiply this three times.

    What does your tri-color LED look like?
    Voltage, current, wattage rating?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Unless your LED has the three colour sources very close together you may need a diffuser. Otherwise you will possibly see three separate dots rather than a colour blend.
     
  5. tioJim

    Thread Starter New Member

    Nov 12, 2014
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    Hi thanks for prompt reply. I don't have specs to hand as I just pulled one out of my component bin, I'd buy some new ones so I can be sure of the specs. If you meant how does it look literally, like a normal clear LED but with four legs.
     
  6. tioJim

    Thread Starter New Member

    Nov 12, 2014
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    Thanks, yes I noticed this fiddling around with the one I do have. Are there two separate types of RGB LED then? One with obviously separate light sources and one with a combined (or seemingly combined) source?

    Thanks
    Jim
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    There are several formats of LED.

    The key for color-blending LED as opposed to a multi-color indicator LED is that the former has the three dies in close proximity AND a wide angle beam (> 120 degrees). Simple indicator LEDs are generally quite a bit less 60 degrees to as little as 20 degrees. These narrow angle LEDs have a huge area of each color that us not overlapped with another color.

    Good color blending LEDs are in flat packs instead of the indicator (bullet) style.
     
  8. tioJim

    Thread Starter New Member

    Nov 12, 2014
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    Great info, thanks!
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Maybe 3 voltage controlled PWM ckts. controlled by 3 sawtooth or triangle wave gens. with slightly different clock rates.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Might try 3 voltagr controlled PWM ckts.( Bill's Index, scroll down to LED's 555's, PWM -___ . to ch. 5 fig 5.3 ) use 3 more 555's to create ramp generators for V inputs.
     
  11. eetech00

    Active Member

    Jun 8, 2013
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    Hi

    CREE makes an RGB LED. See CLMUC-FKA.

    eT
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    He could use one triangle wave for all three. He would just need a comparitor and adjustable reference voltage for each color to set the duty cycle of each.
     
    Bernard likes this.
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Yes, one 555 for PWM around 300 CPS, & 3 ea 555's with slightly different periods, around 1 or 2 sec.
     
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