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lights synchronized with music

Discussion in 'LEDs and Optoelectronics' started by foTONICS, May 18, 2012.

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  1. foTONICS

    foTONICS

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    9
    Sep 30, 2011
    So I'm trying to develop a circuit that will allow LED's to turn on and off depending on what the frequency is. I have decided to split the circuit into three parts; the first one detecting anything from 0hz - 2kHz; the second stage detecting 2kHz - 6kHz; and the last stage detecting anything over 6kHz.

    I built a little demo board of the low pass filter and although it worked I wasn't getting the rolloff that I wanted. Hence I decided to cascade two filters and see if that helps.

    Here is what I have so far:

    *Soon to come: a bandpass filter for the second stage and a high pass filter for the top end*
     

    Attached Files:

  2. foTONICS

    foTONICS

    332
    9
    Sep 30, 2011
    now at the right where it says 'relay' may not necessarily be a relay but just something to manipulate the light
     
  3. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Look up active filter and Sallen and Key. As long as you are using opamps, you can make much sharper filters than what you have shown here.

    Bob
     
  4. KJ6EAD

    KJ6EAD

    1,114
    159
    Aug 13, 2011
    For color organ type applications it's best not to have the filter Q too high to avoid dead gaps between bands.
     
  5. foTONICS

    foTONICS

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    Sep 30, 2011
    I put a cap on the audio in just to keep the dc out, is that part necessary?

    and although i do want a little bleeding into the the next band when i tested this it was going all the way into 4kHz
     
  6. foTONICS

    foTONICS

    332
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    Sep 30, 2011
    update

    so i changed this into a sallen key configuration. it mentioned that the knee is reduced but my question is by how much, is it a huge difference?

    I have attached a picture with the new circuit, i havent changed the values to achieve the frequencies I talked about earlier, I just wanted to make sure I have built it right
     

    Attached Files:

  7. foTONICS

    foTONICS

    332
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    Sep 30, 2011
    frequency response graph

    So I cleaned up the circuits a little, added some values to the components and gave it a test run. At first I had pins 1 & 5 tied to ground but for some reason that was causing a lot of heat to build up in the LM741. So I just left them open and tried again.

    Attached is a graph of Vin against Vout and the corresponding frequencies. I was going to do the frequencies on a logrithmic scale but since this is a low pass filter that I calculated to stop at around 1.5kHz I figured there would be no sense in that.

    Criticism is welcome
     

    Attached Files:

  8. foTONICS

    foTONICS

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    9
    Sep 30, 2011
    circuit

    Just realized I never attached the drawing of the up to date circuit

    In the test run I removed the cap between the audio and ground in addition to the connection between pins 1 & 5 and ground
     

    Attached Files:

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