Control 8x8 RGB LED Brightness

Discussion in 'General Electronics Chat' started by Circuits101, May 6, 2010.

  1. Circuits101

    Thread Starter New Member

    Feb 24, 2010
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    I found on instructables an 8x8 led matrix which uses shift registers to address each individual led. I modified the design so that it uses rgb leds instead and is controlled from a pic18. What I would like to do is be able to set each led at different brightness levels so that I can get a fading effect in some animations. Would i need to replace the shift registers with a multiplexer and added a bunch of external PWM ICs to the design.

    Regards,
    Circuits101
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Post the datasheet of your leds as we can make a better description of possible solutions.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    If your components are fast enough, you can use PWM to flash your leds so fast, It looks always on. By changing the duty cycle, you can dim the LEDs.

    Im with mik3, do you have a datasheet?
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    A multiplexed display is already dimmed with PWM.
    The circuit must blast a high current to the LEDs to make them appear normally bright.
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    I figured the OP may not have known about the duty cycle part of the equation, so I started from square 1.
     
  6. Circuits101

    Thread Starter New Member

    Feb 24, 2010
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    I'll try increase my cycle times and see if PWM in a multiplexed system will work
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    PWM can reduce the average power fed to an LED or to a DC motor.
    A multiplexed array of LEDs is dimmed by the low duty-cycle of the multiplexing.
    PWM can dim the LEDs more but cannot make them brighter.
     
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