What you can do is to measure the voltage over the current sense resistor as the this voltage will have a linear relationship with the output current. But you have to ground reference this voltage and apply some gain to this volage so it fit your ADC range. If you look at the datasheet for LM324
http://www.ti.com/lit/ds/symlink/lm324-n.pdf You can use figure 32 or 38 for this. Any single supply OPAMP can do the job here as long as you stay inide the input Common-Mode Voltage Range given in the datasheet and of course also the supply volage. That will be the same as IC1 and IC4 use. If you want to measure the negative rail with the same micro controller this voltage will need to be inverted