Measuring power consumption in Arduino and raspberry-pi system
Linear make a range of high-side current monitoring devices. 



Figure 1. Linear LTC4151. 0.02 Ω is probably for a high current.

This particular one seems to use serial transmission. Analog versions are available too.

That will give you the current. For power calculation you will need to measure the voltage too - probably from before the voltage regulator so that you measure the losses there too. You then calculate power from \$ P = VI \$. You will have several problems to address including how you average out the current if it varies rapidly.


  ... feedback input to the Arduino to control some sensors.


Generally you will be reading sensor rather than controlling them.