I've lately been exploring very low power microcontroller applications. There are so many situations that fit the form:
- Take a sensor reading.
- Process, store, and/or respond to the sensor value.
- Sleep until interrupt, then repeat.
Simply powering a resistive voltage divider could take on the order of 100 microamps. That's actually significant compared to the sleep current of an ATmega328P controller. The typical solution is to switch the high side of the voltage divider with a P-channel MOSFET. The divider (or resistive sensor) can then be powered only for the duration needed to get a stable sample. See the following:
Reading from a µCurrent GOLD show single digit nanoamps when the divider is off and 1+ milliamps (I badly need a scope!) when on and charging the gate cap back up. Mission accomplished!