Sound Analyzer

Discussion in 'The Projects Forum' started by LoveElecs, Dec 17, 2014.

  1. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    Hello everyone. I am currently working on a project and I don’t know where to begin.

    The purpose of the project is to compare a relative sound frequency to my sound reference frequency. Once the circuit detects the inputted sound frequency equals to my reference frequency, then the signal will send the signal to a MCU to start the operation. I don’t know how to start especially in frequency comparing. This is urgent.

    Basically I have a microphone, a led for indication.

    Thank you for your response.

    :)
    :(
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    You could start by reading this PDF for a tone decoder.
    This type is a bit outdated
    E
     
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How about an analog narrow bandpass filter (uses opamp, Rs and Cs) , followed by a peak detector (a form of AC to DC rectifier, uses opamp, diode, Rs and Cs). This can be read by the MCUs ADC, comparitor, or even a digital input port pin.
     
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  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Could you just send the sound signal to the MCU and let the MCU analyse it to determine frequency?
     
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  5. DickCappels

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    Aug 21, 2008
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  6. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    Wow thank you, this actually i am looking for. But it confuses me, is the center frequency is the reference frequency i wanted on my design? I am planning to make it 40Hz. Like in the circuit i inserted in here? it shows the 3khz and so on. Thank you. [​IMG]
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The circuit you posted is more complex than you need. First, it has three channels; you need only one. It has a pre-amp IC1a, which you may not need.
    It requires a 12V supply; yours is likely 5V. It's lowest frequency channel is centered on 100Hz, you want 40Hz. It drives LEDs; you want a logic level output compatible with a MCU.

    What you have not told us is the required sensitivity (smallest signal to be detected), and bandwidth (how close to 40Hz does the signal need to be and still be detected)?

    How much work are you willing to do, or do you just want to copy a circuit without understanding it?
     
  8. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    Yes an Led for indication that the ~40hz(Or closest to 40Hz) has been detected. And yes a logic level that is compatible with mcu.
    A bandwidth that is close to 33Hz up to 50Hz might work. And sorry, i am not familiar with this circuit. Can you please explain to me the Sensitivity? What sensitivity you are trying to say? i really don't have idea. Thank you...
     
  9. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    In this circuit? Is the center frequency and the reference frequency i am aiming is the same if i follow the mathematical procedure written on the link http://www.ecircuitcenter.com/Circuits/MFB_bandpass/MFB_bandpass.htm ?
     
  10. MikeML

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    Oct 2, 2009
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    the required sensitivity (smallest signal to be detected)? How many V or mV?
     
  11. MikeML

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    Oct 2, 2009
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    Yes. You will have redesign the circuit to be centered at 40Hz, and then determine if the resulting circuit has a sufficiently narrow bandwidth to meet your specs.

    That still leaves the question of the rectifier part of the circuit. Is the simplistic diode in the posted circuit sufficient, or do you need the higher sensitivity offered by the active peak detector I linked to earlier?
     
  12. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    I get it! it is about mV! :)
     
  13. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    I think a peak detector will do.
    Can you please explain to me it further?


    "determine if the resulting circuit has a sufficiently narrow bandwidth to meet your specs."

     
  14. MikeML

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    Oct 2, 2009
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    You need to understand Q and bandwidth of your filter. Google these terms.

    Some reading for you
     
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  15. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    Now it seems like things are clearer now. Thank you.... :)
     
  16. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    Hello! I urgently needed help. I am done with the filter redesign. Then next is the peak detector circuit. I am confuse where to place the peak detector circuit? before or after the filter? Here is my block diagram.
     
  17. MikeML

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    Why did you put the peak detector (rectifier) ahead of the filter?
     
  18. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    That is why i am asking sir. So it supposed to be after the filter sir?
     
  19. MikeML

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    Do you want to detect the unfiltered signal, which has all frequency components, or the filtered signal, which has only a narrow band of frequency components?
     
  20. LoveElecs

    Thread Starter New Member

    Dec 15, 2014
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    I think it is Unfiltered sir which has only a narrow band freq components.
     
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