Dividing and Multiplying Voltages

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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

 

[CWatters]

For the multiplying & division's parts, please give suggestion for the
circuit.

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

 

[Jim Thompson]

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

And then there are slide rules ;-)

...Jim Thompson