Charles, ref your schematic from AOL now

I like the project idea but not the way you propose to implement.While you prefer to adhere to your old known (devils better than …!? ) tested paths,
I prefer not to compromise for :
1) reliability, for which parts count is optimised: for this reason and others,I prefer to use 6 consecutive lines of microcontroller for LCD.May be for this another 2051 will be required,since the whole idea is to exploit AIN0 and AIN1but two Ics U7 and U9 are eliminated.In fact I curious when,if at all,use of them are justified except for students.
2) For the same reason I wonder why use U10 and XTAL2? I believe the product 2Hz going to INT0, is used refresh rate of LCD and or sampling.But then why can’t we do it internally, by the microcontroller itself?
3) For the same reason I wonder why use U12 at all ,if it is switching inputs only? Why dont the three inputs,voltage-current-refresh rate(if generated externally) go to three separate pins of microcontroller?
4) Safety: While I admit my limited experience in this type AC measurements, I cannot put up with direct AC connected to electronic instruments without binding reasons.Small isolation (1:1)transformers are essential.
5) Half Wave Rectification: A total of 5000µF is proposed?How much is the current these electrolytics have to smooth?What is the rule of thumb?
6) 1N4001 in power supply: Bridges?
7) D6 :Redundant.
8) 50MVFS: Is it 50µV F.S.D.(full scale deflection)?
9) PIN 3 of LCD : It is contrast not brightness.Usually works at less than +1v.Your P2 10K preset will be difficult to set if not multiturn.
10) R2 :Will control brightness.Usually 27 Ohms.
11) S8,S9:??
12) Most Important:Where is the capacitor 0.1µF decoupling the microcontroller?
I have experience in Analog-to-Digital Conversion Utilizing the
AT89CX051 Microcontrollers, and a lot of questions.Incidentally there was an article in EFY some times ago in the same line.Do you care?
To err is human.I stand to be corrected.
Best Regards
A.S.Rudra