Advanced LED throbbing and color organs

Discussion in 'General Electronics Chat' started by Wendy, Jul 3, 2010.

  1. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    OK, I am working on my article LEDs, 555s, Flashers, and Light Chasers (forum edition) again, and am trying to come up with some new schematics.

    There are two problems, both are similar, I want to make a circuit that will flash the LEDs in time with music. I also have another application where a straight audio signal is feed into them and make them flicker like a fire.

    Here is my thoughts at the moment..

    [​IMG]

    Circuits 1, 2, and 3 are alternate ideas, where a stereo feeds into them and they feed into example B.

    Circuit 3 is my best contender, it doesn't use any rectification, but only depends on the music peaks to make the LEDs vary intensity. The diodes are for protection from over driving. Give the size of the resistors it isn't likely, but cheap protection.

    Basically I want something as brute simple as I can come up with, this is meant for beginners after all (though this is more into medium electronics).

    I'm looking for holes in my idea, and possible ideas for improvements. Parts count is critical, fewer is better even if performance suffers a little.
     
    Last edited: Jul 3, 2010
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello Bill,

    Did you also think of the filters to be used for the color organ?
    I have attached some PDF's that might interest you.

    Bertus
     
  3. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    Thanks guy. I'm looking more on the conversion from sound to light at the moment, I'm going to mention it is the second half of a color organ in my article (and then leave off the filters).

    Thanks for the links though. If people express enough interest I may pick it up in a separate chapter, though it is straying pretty far from the theme of the article. The page count is getting up there, if I increase it by X50 or so I will have an honest book!
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    I think a peak detector is important so that short duration peaks in the music turn on the LEDs long enough to be seen brightly. Without a peak detector then the LEDs are frequently a dim blur.

    A single supply opamp like an MC3317x or MC3407x can be used as the amplifier and rectifier since it can be biased at ground and its output goes to ground.
    A poor performance LM358 or LM324 opamp could be used if you don't care about high audio frequencies.

    Maybe an automatic gain control is needed so that the LEDs are not turned on all the time if the music is loud and they are not turned off all the time when the music is not loud.
     
    Last edited: Jul 3, 2010
  5. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    Both of those are valid points. I could add the second half circuits 1 and 2 have to circuit 3 for the throbbing effects.

    I'm not too worried about frequency response in this tutorial. I suspect the role off will be bad even by my loose standards if the gain is set high as it probably will be. I mainly want something that can be adjusted over the full range.

    I like the AGC idea, something to keep in mind for better circuits eventually. For this I'm trying for simple. Thoughts on how you would do it?
     
  6. bertus

    Administrator

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    Hello Bill,

    Here is a PDF with some AGC theory and circuits.

    Bertus
     
  7. Audioguru

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    A Jfet has been used over the years as an AGC device (a voltage-controlled attenuator) when fed the rectified signal.

    I was wondering what "Trobbing" is but it was a typo and is actually "Throbbing".
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    'Pulsating' seem much more of a 'G' rated word than 'Throbbing'.

    I was hoping it was a new word and not a typo... oh well. ;)
     
  9. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    Collins Radio used the darnest AGC scheme I've ever seen with pilot lights, little light bulbs. It was primitive, but it worked. They even had the bulbs in series with the 70Mhz RF (which was the IF frequency for the land lines and satellite receivers) that were treated like variable resistors.
     
    Last edited by a moderator: Jul 3, 2010
  10. Audioguru

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    The very first product from Hewlett-Packard was a Wien-bridge oscillator (using vacuum tubes) that used a lightbulb for amplitude control. The amplitude bounced a lot when the frequency was changed then it gradually leveled out.
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    As a suggestion, see if you can't rig up an ECG input to make the LED's flash. I guess an alpha wave headband input should follow, too.
     
  12. Wendy

    Thread Starter Moderator

    Mar 24, 2008
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    OK, here is what I've come up with for the high power unit.

    [​IMG]

    This isn't really finished, I need to define an op amp, pinouts, and power supply leads. The concept is there however.

    I could do a simple unit using a single op amp, but I would like to use a transistor or two.
     
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