Am I missing something here?... I would just use a Small series resistance on the negative common line and use a simple Op Amp to boost the voltage reference off of it to the levels the ADC needs if it is not capable of reading mv levels directly.)
Its just been the blank picture symbol since this thread started.
Apparently you can see something I dont.
Then never mind me if it is already what I was talking about.
Scene 1: When mike posted his schematic with op-amp mapped to 0-5V, i tried to simulate the same in Proteus with R-R op-amp TL2272 but its output never touched full positive rail. but when the supply voltage is increased to say 7.5-9V the O/P swing to +5V, if that's the case then why can't i use the "humble" LM358.
Scene 2: i now want to scale everything to 0-2.56V, so that 1.28V-2.56 maps -12.8A and 1.28-0V maps +12.8A, +-100mV indicates +-1amp, but in use i want to hit +-10A only and balance +-2.8A is just for max range.
on the ADC side it can be configured as 8 bit or 10 bit, but for this above use i want it to be as 8 bit ( 2.56V/ 256steps = 10mV/step) that's sufficient resolution to show 1 place after the decimal like 9.9amps.
Thank you Mike and Roff for helping me and clearing my doubts, at last i could do what i wanted and that too using low side sensing. i have rescaled the setup to 2.56V ADC's ref, and calculated the potential divider values, here's the circuit in action
now i need to try out in real hardware with the AVR.......
Thanks once again to you folks especially Mike (who has lots of patience)