in order to facilitate the development of any kind of battery powered sensors (or actuators), I have designed this small pcb that can be easily placed in a 3d printable case

The main features are:

• Small dimensions: 55 x 35 mm

• Multiple power options: 2 x AAA batteries or 1xAAA battery (Rechargeable or Alkaline), 1 x CR2032 battery, standard cellphone charger at 5V through the micro USB port or through Vin and GND pin of the MYSX connector

• Reverse polarity protection (Mosfet Q1) to prevent damages in case of wrong batteries insertion.
  Boost converter (ME2188C33) to increase the battery voltage to 3.3V when necessary

• LEDs for radio traffic and low batteries signaling. All configurable in the firmware.

• Multiple radio module supported: NRF24L01 (SMD and THT) and RFM69.

• Footprint for a reed switch

• MYSX connector v.2.6

• Support for ATSHA204 chip (security and signing)
  Mounting hole for a M2.5 screw

Probably in this days the ATMega-328P is a sort of "old" technology but for simple battery powered devices it remains a good option, also for its easy of use.

If someone is interested, all the informations and the links to technical files (kicad project, gerber, schematics, firmware, etc) are in the dedicated wiki page of the d-diot project.