Dear Rauf,

That's nice, but even the iput of the Op_Amp has to be controlled digitally from 8051.

And it comes to D to A conversion. The simplest and lowest cost solution is to do an R-2R staircase.

I have already floated my problem to Gurus (including Steve). I pray they help me.

In the mean time I am trying to make an equivalent circuit of AD ICs by copying their internal R-2R circuit and using analog MUX. If it works the price comparison would certainly be 1:7 :))

Kindly you also give it a try if you find time.

I will reply you to your direct email addy regarding book matter.

Thank you.

Babar/