System configuration
A system that includes power consumption constraints in its specifications must be designed to meet the requirements in all its aspects, including hardware, software, and mechanical design. The selection of components and peripherals must take into account their energy profiles. External peripherals are often the most power-demanding components, and thus their power source must be interrupted by the microcontroller when they are not being used.
Hardware design
In low-power embedded systems, the hardware design must include the possibility to power on/off peripherals using a GPIO pin. This is better done using a line that is normally low, so that it can be pulled down using passive components when the GPIO is not driven by the microcontroller. MOSFETs are often used to control the power supplied to external peripherals, using a GPIO signal to control the gate voltage.
Even when peripherals are turned off by interrupting their power source line, smaller currents may leak...
