Led fading circuit

Discussion in 'The Projects Forum' started by brozizds, Dec 15, 2010.

  1. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Hi again,
    I'm in need of help again I am building a picture frame to be lit with 48 3mm leds containing 16 red, 16 white, and 16 blue, which will be installed on the perimeter of a piece of etched plexiglass in the frame. my question is what type of circuit do I need to have the leds fade in and out respectivily red, white, and then blue. speed control is not that important but would be nice. Can I build this myself or buy a kit? If I can build it myself can someone submit a schematic? Thanks Jim :)
     
  2. Wendy

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  3. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Thanks Bill ,
    As I said at first I want to have 16 leds at a time fade in and out to next color and keep repeating. I went to the link you posted and found the comet trail but I dont think that will work to light up the etching on the plex . Can you help me with this? Thanks Jim
    PS What a great set of applications!:)
     
  4. wayneh

    Expert

    Sep 9, 2010
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    You're going to want 3 (one for each color) MOSFETs under PWM control. For power, you might be able to use 12v across 4 sets of 4 LEDs in series, again for each color.

    I'm hazy on how you'll generate the control signal to vary the PWM but I'm sure someone here will have an idea.

    A clever design might be able to use a single MOSFET but this might complicate the design of the controls. MOSFETs are darn cheap, so just use 3.
     
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  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Something like This may be of interest. The EL outputs are 3V, and could be boosted with a transistor to drive a MOSFET.

    If you only want to control 3 lines to fade, then an 8 pin PIC could provide the PWM to drive transistors or/and MOSFETs to the voltage/current you need. An Arduino is also capable of this, depending on your familiarity with software/hardware hybrids.

    Did you want the 3 colors to fade all together, or have each LED fade independently of the rest?
     
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  6. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Thanks TOG,
    I do want them to fade from red to white then to blue. TY again Jim:)
     
  7. thatoneguy

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    Did you want to use RGB Leds where all of them faded from dark to bright red, back to dark, then to bright white, then fade back to dark, then to bright blue, and start over?

    Or the similar concept with 3 separate strings of Red, White, and Blue LEDs where one string would fade to bright, then back to dark, and the next string fades in and out, etc?

    I'm not sure if you want the fading to be on the "on transition" or the "off transition", or both.

    Doing both would pretty much require a microcontroller. Something like an Arduino is user friendly to start with, you'd only need to use the transistor driver parts of Bill's circuits to drive them.

    How much time/money did you want to invest in this?
     
  8. Ron H

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    Apr 14, 2005
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    You need to define your fade pattern a little better. Do you want each color to fade completely before the next one starts, or do you want some amount of overlap?
     
  9. Wendy

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    Instead of the comet trails look at "RGB LEDs (Millions of Colors)", it is a lot closer to what you were describing.
     
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  10. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    The light pattern is as in my 1st. thread , red 1st. form off to bright then back to off, then white off to bright then back to off, then blue the same and then repeat the pattern. 16 of each color for a total of 48 LEDs. Thanks Jim
     
  11. brozizds

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    Aug 15, 2010
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    and yes Im using 3 seperate strings containing 3mm LEDs @ 16 per string. Thanks Jim
     
  12. Wendy

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    Red, White, Blue. Got it. Might be able to do it with some tweaking. I'll think about it.
     
  13. Ron H

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    This technique should work. Some details need to be filled in.

    EDIT: I also ran a simulation, with some values changed to make the sim run faster. See the attached .ASC file.
     
    Last edited: Dec 16, 2010
  14. Wendy

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    That is pretty close to what I was trying to think of. Mind if I redraw it and incorporate into my 555 article Ron?
     
  15. Ron H

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    I think you should.:D
     
  16. thatoneguy

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    That's a nifty solution. 4 ICs (using a 556) and some passive components saves problems with programming or remembering which program was loaded onto a PIC. :D
     
  17. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Thanks Guys,
    The schematic looks great , but please remember (NEWBIE)there are some components there I'm not familiar with. PS. Ron I tried opening your attch. but couldn't. Bill I did a proto in chap.12 with the single red led (throbbing LEDs) and thats working! lol :confused: but I'm still a newbie:rolleyes: Also I noticed that by changing the value of C1 it changes the fade time!And Bill could you post your re-draw?
    Thanks Jim
     
  18. Wendy

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    Mar 24, 2008
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    What is your power supply voltage?

    How long per each fade on/fade off cycle (in seconds)?

    I'm assuming 20ma per LED unless told differently.
     
  19. Ron H

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    I should have mentioned that the .ASC file runs on LTspice, which is a free simulator from Linear Technology.
     
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  20. Wendy

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    OK, first drawing done. All those designations are a PITA.

    [​IMG]

    Looks like you found a use for those CMOS 555's you ordered.
     
    Last edited: Dec 17, 2010
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