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Dividing and Multiplying Voltages

Discussion in 'Misc Electronics' started by [email protected], Dec 15, 2004.

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  1. Guest

    Hi mates.

    Albert's here. I'm new here and i'm seeking your helps regarding the
    following.

    I'm working on a project which involves the arithmetic operations (+,
    -, X, /) on voltages. Using ADC conversion is not applicable in my
    case. The project is to capture 4 voltages from 4 testpoints from a
    PCBA, ie A, B, C and D. After capturing the 4 voltages, we need to do
    the following calculations:

    Result = ((A+B)-(C+D))/(A+B+C+D)

    For the addition and subtraction parts, i've got the idea of using
    summing amplifier and inverting amplifier to perform the functions. If
    you have other suggestion, kindly share with me. Fyi, the voltage
    values are about 0.3V.

    For the multiplying & division's parts, please give suggestion for the
    circuit.
    Thanks and hope to get your response soon.

    Cheers,
    Albert Leng
     
  2. CWatters

    CWatters Guest

    Is this for a test/homework or do you actually just want to build it? The
    answers would be different :)

    Homework answer: Investigate Logarithims.

    If I remember correctly (it's been a while)....

    LOG(A*B) = LOG(A) + LOG(B)

    so A*B = LOG^-1 (LOG(A) + LOG(B))

    Also for division..

    LOG(A/B) = LOG(A) - LOG(B)

    so

    A/B = LOG^-1(LOG(A) - LOG(B))

    If you wnt to build something...

    Here is another approach that avoids logs...

    http://www.edn.com/archives/1996/101096/21di_01.htm

    There are commercial chips to do the job. Perhaps one of these black
    boxes...

    http://www.analog.com/en/subCat/0,2879,773%5F862%5F0%5F%5F0%5F,00.html
     
  3. Jim Thompson

    Jim Thompson Guest

    And then there are slide rules ;-)

    ...Jim Thompson
     
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