PK-RF-Sense is optimized for low power, which is essential for wireless sensor networks. It uses an ultra low Iq boost converter to get the 3.3V for the PK-RF-31 and the sensors.
As an storage device, a couple of rechargeable AA battery can be used, or even some supercapacitors. The board size is the same as two AA battery holder and it has the connector to fit that battery holder, so it is ideal. The charging process will be controlled by the PK-RF-31, it will monitor the voltage and then a mosfet will act as a switch to let the current flow. The input source shouldn´t work above 3v3, as there is no capability of lowering the voltage. I didn´t use a zener to avoid current leakage, and probably I will check for ultra low Iq buck/boost converters for the next version.
The device also has a serial/USB connectivity. It has an FTDI converter integrated which is ideal for debug purposes or when the board is used as a gateway in a PC or Raspberry-PI.
When USB is used, PK-RF-Sense has also the capability of charging the storage device. To avoid excessive currents from the PC/Rpi a current limiter is included.