Power Selection Module
Power inputs must be between 4.4v and 5.7v
Power output is the same voltage as the selected input.
Power can be taken off the PSM in different methods, allowing for different subsystems to fail gracefully.
This module also holds the Buzzer controller.
The Aux power input has a Zener clamping it to 5.6v, this zener is protected from continuous over voltages by a fuse and fet.