ATMEGA32U4 microcontroller, all in one USB communication no need for external FTDI chip.
mini USB connector
Input power supply 7-12VDC
ULTRA LOW POWER voltage regulators and the consumption is only few microamps, which enables hand-held and battery powered applications.
Li-Ion rechargeable battery power supply option with a BUILD-IN on board charger, so when you attach a battery, it is automatically charged and kept in this state until the other power source (USB or external adapter) is removed and it will AUTOMATICALLY power the board - no jumpers, no switches!
Works both on 3.3V and on 5V which can be selected with a jumper, so 3.3V and 5V shields can be used
UEXT connector which allows many existing modules like RF, ZIGBEE, GSM, GPS to be connected
Allows real-time clock (Q1 can be replaced by RTC).
NOISE IMMUNE design
The LEDs and the button BUT are on the edge of the board so there is easy access even if the boards have shields on them
All of the components are LOWER than the connectors, so that the shields don't interfere with them
Original design had a flaw - the connectors were not spaced at 0.1" which made bread board use impossible, to keep the compatibility we have the original spacing but we also added a 0.1'' connector which customer can use with bread boards (and jumper wires) saving the hustle of soldering
All signals on the connectors are printed on the top of the board, so when you check with a probe you will know exactly which port you are measuring