Hello Asok Sankar Rudra,

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.
I would think the 74LS174 and 74LS08 would be more reliable than another 89C2051. They certainly are cheaper and more widely available than a 89C2051 and don't require a programmer.

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 cant we do it internally, by the microcontroller itself?
ans. U10 is part of a software clock. The other two clocks are already used for RS232 communications and measurement of the incoming voltage. This was necessary because there were no more resources.


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?
ans. U12 is necessary to switch the incoming measure voltage. There is only one place you can measure this voltage (P1.1). I don't understand your reference to using other pins.

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.
ans. Here again I don't think you understand what it is I am doing. There is no direct connection to main!
Just tap across the meter coil movement to differential opamp.
Below are two pictures of the Volt meter and Amp Probe.

amp probe meter

Simpson 260 MultiMeter



5) Half Wave Rectification: A total of 5000µF is proposed?How much is the current these electrolytic have to smooth?What is the rule of thumb?
ans. The power supply is critical for this circuit to work reliably. That's the reason for the 5000 uF electrolytics.

6) 1N4001 in power supply: Bridges?
ans. I have to use diodes (1N4001 in this case) to get the negative and positive voltages. If I were to use a Bridge rectifier I would require a center Tap transformer.

7) D6 : Redundant.
ans. Redundant? not at all. It prevents the battery from feeding voltage into the 7806 regulator.

8) 50MVFS: Is it 50µV F.S.D.(full scale deflection)?
ans. 50MVFS = 50 milli Volts 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.
ans. contrast Vs brightness. So noted. I will correct the schematic.

10) R2 :Will control brightness.Usually 27 Ohms.
ans. This was suggested to be 100 ohms by another forum member. I went with that. I originally had 1000. I guess it will seek its own level eventually.

11) S8,S9:??
ans. Future use. They are being mounted on a front panel and not in use at this time.

12) Most Important:Where is the capacitor 0.1µF decoupling the microcontroller?
ans. I think you are going over kill on these capacitors. I have included three 0.1 uf capacitors (c20, c21 and c22) for bypass


I have experience in Analog-to-Digital Conversion Utilizing the
AT89CX051 Microcontrollers, and a lot of questions.
ans Great, Start another thread sharing your experiences and ask your questions.


Incidentally there was an article in EFY some times ago in the same line.Do you care?
ans. I don't know what EFY is. Do you have a link?
Do I care? I don't know what you are referring to here.

Regards,

Charles Bannister