Albert, I have a few ideas for you.

Any load cell wants to be amplified (usually the signal is 4-10mV FS) to logic
levels.  Since the signal is so small, and the common mode is half of the
driving voltage, an instrumentation amplifier is by far the best candidate for
the job.  Some of the two and three op-amp approaches are OK for experimenting,
but must have the resistors reasonably well matched for good results.  So jump
over to aomething in Analog Devices AD6XX family.  All depends on whether you
have a single or split supply, and what kind of gains you want.

You will probably want to create a fixed precision 10V source to drive the load
cell.  You want something very stabe over temperature.  You might do 5V if the
load cell will work properly.

A second approach is to use a delta sigma meant for this task, such as AD7731 or
AD7705 or another manufacturer (you must keep in mind that Analog Devices is
having a horrible allocation problem right now).  If you do that, the VGA is in
the chip, programmable offset, a reference, a ratiometric arrangement that does
not need a precision voltage drive, and a host of other features.  But this
approach would be if you need 16 or 24 bits of resolution.

Have fun!
Chris Eddy

Albert Goodwill wrote:

> I would like to use load-cell to measure weight, perform some calculation on
> the measured value and display by using PIC16F877.
>
> Any circuit / idea / information regarding front-end circuit for load cell
> interface?
>
> Thanks..
>
> albertgoodwill@yahoo.com
>
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