Audio Bands and LEDs

Discussion in 'The Projects Forum' started by FisherEvans, Oct 30, 2010.

  1. FisherEvans

    Thread Starter New Member

    Oct 30, 2010
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    Hello,
    This is my first post on the forums, and would like to say hello to everyone, and thank you in advance.

    Now, onto the situation. I have no "professional" knowledge of electronics (diagram, components, etc). I merely tinker with them as a hobby. I have related small projects, like a simple 2-channel TIP31 led flasher; a Strobe light with variable speed; a portable audio mixer and a portable USB charger. Nothing real fancy. I would like tog et a bit fancier though.

    I want to make a 5 band, "light organ." Where an output LED would light up depending on the frequency. For instance...
    Audio input, 5 LED strings (not like an equalizer, all light up at presence of the freq. range), each LED string hooked up to light at (for example) Low, Low-Med, Med, Med-High, High Frequencies.

    I have done some research. What I have found is that I will probably use Op-Amps to construct this. How ever, out of all my research I CANNOT find any information on Op-amps. I am looking for equations, and diagrams to determine the frequency of the audio and output.

    I am going to base this project off of:
    http://blog.makezine.com/archive/2010/10/circuit_skills_led_color_organ_spon.html
    http://blog.makezine.com/ledColorOrgan-schem_r1.gif

    What I am looking for is some explanation as to what is going on here, where I can find further research on this idea, and any advice on how to go about this. (I do not want to copy this given circuit diagram, I want to remake it, while fully understanding what is going on here.)
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Look at the feedback capacitors on the op amps in the schematic. Note their values for the different frequencies.

    The op amps are 3 Active Filters , each biased with input and feedback capacitors to limit response range to specific frequencies. Click link above to wikipedia for more info, they also explain op amps fairly well.
     
  3. FisherEvans

    Thread Starter New Member

    Oct 30, 2010
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    Thank you for the quick reply, will go over it tomorrow, it is getting late...
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I would go more in-depth, but the wiki article on op-amps and filter types will probably give you enough background to understand their function, at which point, we can help you add the two additional bands. :)
     
  5. Wendy

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    Mar 24, 2008
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  6. Audioguru

    New Member

    Dec 20, 2007
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    The Wikipedia article has many different kinds of active filters.
    The filters used in the color organ are called Multiple Feedback Bandpass Filters and you can find them if you search in Google.

    The filter circuits should be fed from a low impedance source like the direct output of an opamp, not from the volume controls shown in the project.
     
  7. FisherEvans

    Thread Starter New Member

    Oct 30, 2010
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    Just to confirm, the bias voltage is the audio source, and the Vin is the power source, and the 3 pronged item is a ground... correct?

    And thank you everyone; this circuit is starting to make a lot more sense, gonna go test the output of this.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    No, the "Vin" is the audio input, the power connections for the op amp (triangle symbol) aren't shown.

    The "+" input is the non-inverting input, no phase change on output.
    The "-" input is the inverting input, 180 degree phase shift on output.
    The "point" of the amplifier symbol (triangle) is the output of the op amp.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    Since the (+) input of each opamp has a reference voltage of 0V (ground) then the power supply must be plus and minus type (a dual polarity supply).
     
  10. FisherEvans

    Thread Starter New Member

    Oct 30, 2010
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