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DSP using a non DSP processor

Discussion in 'Embedded' started by Rohan, Sep 1, 2006.

  1. Rohan

    Rohan Guest

    My requirement is to use a moderate controller (Non DSP) and take
    analog sinusoidal signals (half second cycle 50 hz) , take their
    samples, do a Fourier transform to remove harmonics and then multiply
    them to find instantaneous power. Then do a Low Power Filtering
    operation on this power signal.
    Is it possible? has anyone implemented anything similar or am I being
    too ambitious?
    please post your comments about its feasibility.

    Thanks,
    Rohan
     
    Rohan, Sep 1, 2006
    #1
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  2. Rohan

    Donald Guest

    The big question is "in real time?".

    Do you want to do this in C ?

    So, Yea but, is your answer.
     
    Donald, Sep 1, 2006
    #2
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  3. It is possible, depends on your precision, harmonics and samples.
    I've seen some of the better 80C51's used for mains FFT work.

    Look at some of the metering ICs like
    http://www.tsc.tdk.com/products/product_category_detail.cfm?category_key=27
    or
    http://www.austriamicrosystems.com/03products/11_metering.htm

    -jg
     
    Jim Granville, Sep 1, 2006
    #3
  4. Rohan

    Tauno Voipio Guest

    Are you sure that Fourier is the way to go
    instead of a simpler low-pass filter?

    You can implement a quite fancy filter at about
    70 Hz corner frequency with the calculation
    tedium of a FFT / inverse FFT pair.

    The main difference of a DSP to a more common
    processor is the ability to make a very fast
    scalar product of two vectors, i.e. multiply
    the vectors element-by-element and add the
    products. If your application stands doing
    the same with a garden-variety processor,
    you can use it.

    To get a reasonable amount of samples in a cycle,
    you will need a sample rate around 1000 samples
    per channel and second. This is not a problem
    for modern controllers.

    A good point to ponder is whether a 8 bit controller
    can handle it or if a more powerful 32 bit chip
    would better fill the bill. The main considerations
    here are cost and needed calculation resolution.

    (I'd consider some of the ARM's here, e.g. Atmel AT91's).
     
    Tauno Voipio, Sep 1, 2006
    #4
  5. Rohan

    Rohan Guest

    I think low pass filter is a good idea. can you guide me how the FFT /
    inverse FFT pair could give a corner frequency of 70hz. this should
    solve the problem
    I am using a renesas R8C series 16 bit processor. This is the first
    time i am dealing with analog/digital signals so my knowledge is
    limited to the books.
    Its the function of a AD7751 metering IC whose function I have to
    emulate inside the controller.
    Yes it has to be done in real time.
    So logic should be about 1000 samples per second, Low pass filter at 70
    hz, multiply over a cycle and take average? is it feasible?
    And also do ADC give a negative value for negative half cycles. If no
    then how do you take care of it?
     
    Rohan, Sep 1, 2006
    #5
  6. Rohan

    Tauno Voipio Guest

    The filter should be done *without* any Fourier transform
    at all.

    Please get an elementary textbook on digital signal processing
    and learn the filter design. There are quite a lot of different
    design decisions that *you* have to make.
    IMHO, yes. It depends on your other design decisions, however.
    Pretty many ADCs can be set up for bi-polar operation.
    Have a look at the manual of the converter you have.
     
    Tauno Voipio, Sep 1, 2006
    #6
  7. I have designed a similar (but quite simpler) system. The idea is in
    using fast FIFO memory to read from ADC and hold a signal and then
    operate with data in non-real time by slow mcu.
     
    Eugene V. Upenik, Sep 1, 2006
    #7
  8. Rohan

    Rohan Guest

    Hi all,
    Thanks for the wonderful support.
    Have got the book and working on my DSP skills. Thats the most
    important first step. Thanks
    hi Eugene. I am also looking at simplifying design. I have to ensure I
    have an average power being calculated every half second. so its like
    non real time. could you guide me a little more about what kind of
    system you are using. I couldn't get the logic from your post.
    Thanks a lot
     
    Rohan, Sep 1, 2006
    #8
  9. Look here. There is a reference design available.

    http://www.maxim-ic.com/solutions/electricity_metering_system/index.mvp

    Mit freundlichen Grüßen

    Frank-Christian Krügel
     
    Frank-Christian Kruegel, Sep 1, 2006
    #9
  10. Rohan

    werty Guest

    C dont do machine code , Forth does .
    H/w is too cheap to ignore ....

    _____________________________________________
     
    werty, Sep 3, 2006
    #10
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