9V Battery Step-Down Power Supply

This handy little gadget snaps onto the top of a 9V battery and provides either 5.0V or 3.3V, selectable by a solder jumper. It is a high efficiency switching supply and it can extend the life of a 9V battery up to 2.5x at 3.3V and well over 1.5x at 5V compared to using a high-quality linear low-dropout regulator (LDO). It only consumes an amazing 3 uA with no load, which is what the self-discharge rate of an alkaline battery is anyway! It is perfect for powering an IOT sensor from a convenient rectangular form-factor single 9V battery instead of multiple cylindrical batteries like AA's. It can provide up to 350 mA of output current which is plenty to power a WiFi radio. There are two JST PH headers on the top, one for the regulated output and the other connected directly to the 9V battery for powering motors or solenoids or monitoring the battery voltage. All of the components are underneath, leaving a very thumb-friendly surface to press on when snapping it onto the top of the batte