Op Amp with PIC for high input risestance

[Ayne]

This is my idea.
I want to use pic16f877a as a volt meter
Does this circuit will work?
i use this circuit for higher input resistance...
for higher ranges of input voltages i will change the value of R2..
I know the way for changing this resistor by a selector switch...but there is any way to change this electronicaly
i needed ur help...

If u have better ideas to use pic16f877 as a volt meter than plz share ur ideas..
Thanks in advance.

 

[Optikon]

This is my idea.
I want to use pic16f877a as a volt meter
Does this circuit will work?
i use this circuit for higher input resistance...
for higher ranges of input voltages i will change the value of R2..
I know the way for changing this resistor by a selector switch...but there is any way to change this electronicaly
i needed ur help...

If u have better ideas to use pic16f877 as a volt meter than plz share ur ideas..
Thanks in advance.

A very crude volt meter... If you will use just a single part consider using an instrumentation opamp.

Or, consider using non-inverting configuration for high input impedance (your configuration is considered pretty low IMO)

Consider also overload voltages to protect your amplifier & microcontroller inputs. Put some protection in there. Also, the 741 is a pretty lousy opamp. Use something better, there are lots better that are low cost.

If you will not be calibrating, you will need low offset voltage, low drift types if you expect correct voltage answers.

Also, what do you expect it to do with an AC signal? Do you want filtering?