Please help in a project which can give constant level of volume at its output whether the input volume level is increased/decreased (within certain limits) and microphone should act as input device.
The out put volume level should be automatical maintained at fixed pre-determined level without any manual adjustment required.

P.S.- Please start from very basic and speacial consideration towards power consumption

 

Microcontroller.

 

A microcontroller might form part of such a system but purpose-designed ICs are made for such functions.

It might be easier for the OP to use something of this kind - less design effort.

Here is an example - not a recommendation: I just Googled audio AGC IC http://www.analog.com/static/imported-files/application_notes/AN_934.pdf

Edit: You can probably find others which would be much simpler to use: http://datasheets.maxim-ic.com/en/ds/MAX9814.pdf

 

The words, "automatic level control" or "automatic gain control" are good ways to start. I played with some of those chips 30 years ago when I worked with a band. (They aren't very good for musicians.) Let's see...NE570 or SA571 compandor. There's a cute word. compressor-expander = compandor
I don't think Signetics makes those any more.
H*** I'm so old I don't even know if Signetics exists any more!

 

Signetics was acquired by Phillips Semiconductors (now NXP) in 1975; the brand continued for several years, later becoming fully integrated. In 1995, NXP spun off the Korean assembly and test operation, who continues to use the name "Signetics"
Source: http://en.wikipedia.org/wiki/Signetics