Dividing and Multiplying Voltages

albertleng 21 years ago

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

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CWatters 21 years ago

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)

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

If you wnt to build something...

Here is another approach that avoids logs...

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

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Jim Thompson 21 years ago

And then there are slide rules ;-)

...Jim Thompson

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