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  1. #1
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    Analog circuitry analysis

    Hello fellows,

    I have the attached analog circuitry attached to an ADC, I am trying to understand what each step does, i figured out a couple but i am really struggling to understand the others (not so good with analog circuitry) I wish if someone can help telling me what each op Amp does to the signal.

    the sensor i have is an accelerometer and its piezoelectric, will attach its response as well as the response at the input of the ADC.

    the current ADC is https://datasheets.maximintegrated.c...06-ICL7107.pdf, and I am trying to use a PIC MCU instead so any suggestions are welcome.

    Regards.

    Schematic : Click image for larger version. 

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    ADC input: Click image for larger version. 

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    Sensor Output: Click image for larger version. 

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  2. #2
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    Re: Analog circuitry analysis

    Hi,

    * J1 is the input
    * C7, C8 are input filters, they suppress high frequencies. There is no series resistor, thus one can not calculate a upper cutoff frequency.
    * R11 ensures zero level on idle
    * IC2 (R12, C18...)is an integrator for the frequencies of interest.
    * IC1 is a very low frequency feedback for the integrator to prevent the integrator from run away. It ensures precise zero level on idle.
    * IC3 is a 2nd order lowpass filter.

    now I have to guess:
    I assume IC4 combined with IC5 is some kind of peak_detect_and_hold circuit. But Iīm not sure.
    Maybe it is used to make the peak value readable at the 7107 display. .. then the value decreases slowly.


    ***
    If you want to use a microcontroller, most of this analog circuitry can be replaced by software... with higher precision...

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


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  3. #3
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    Re: Analog circuitry analysis

    Thanks a lot Klaus.

    I am trying to connect this to a MCU, so was thinking of this circuitry:

    Click image for larger version. 

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    the voltage might spike to 10v out of the sensor so i need to adjust it as i am using a 5v PIC MCU.



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    Re: Analog circuitry analysis

    Hi,

    With this circuit you see the positive signal only.

    You donīt get exact 0V on idle.
    -> Check OPAMP datasheet.
    I recommend to add some bias voltage at the analog side and subtract it at the digital side (software)

    The zener combined with the 50k source impedance will distort even much lower (than 10V) signals.
    --> check zener capacitance.... and zener V-I diagram.

    Klaus
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