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Noise problems that may occur during the ADC using the MCU itself

SukHwan Jung
Prodigy 30 points
Other Parts Discussed in Thread: MSP430F5529

Hellow

I am a student ongoing research on voice signal processing

I am working on a project that outputs a maximum frequency after performing the 'FFT' receives a sound signal by using 'MSP430F5529 USB LaunchPad Evaluation Kit'. Understandably, I was trying to use the ADC port of MCU to be used as input to the microphone. But without any other input pin of the MCU ADC it has caused periodic noise about 1.3V. Even occur without attaching a microphone. Now this problem has been acting as a major problem in the low-frequency (20 ~ 90Hz) FFT.

This is a situation that is now occurring in two identical modules that I have. Is it a problem if the module itself?

  • 0
    Guru 74080 points

    What type of microphone are you using?

    SukHwan Jung said:
    Even occur without attaching a microphone.

    Does that mean with open input of the ADC? A high impedance input always picks up all sort of crap from it's surrounding. The input needs a defined potential. Floating is not an option in your case. And that is why I asked for the type of microphone. Does it drive the input or how is your configuration? Do you have a schematic?

    Dennis

  • 0 in reply to Dennis Eichmann
    Prodigy 30 points

    Hello Dennis

    I using the microphone receives the sound causes a change in the output voltage of the microphone. Unfortunately I do not have a schematic of a microphone (not available from the manufacturer.)

    I added a picture of the current situation. The first picture is showing the result of an ADC using a microphone. The second photograph was measured by the value of the oscilloscope and remove the microphone input of the ADC pin.

    So I now have the idea that it generates noise on the ADC pin in the MCU itself. Code has the ADC code provided by TI.

    Regards,

    Dennis

  • 0 in reply to SukHwan Jung
    Guru 74080 points
    What is the frequency of your "noise"? Is it the typical 50/60Hz from the power line?
  • 0 in reply to Dennis Eichmann
    Prodigy 30 points
    Mainly 200Hz. When measuring the frequency of 20 ~ 90Hz, FFT result of 200Hz will be output.
    However, the output frequency is 100Hz more input signals without noise and almost exact value.

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