This is a 3.3V Arduino running the 8MHz bootloader. Because the system voltage for this board is lower than other Arduino development boards, it may not be compatible with many Arduino shields which were designed to run at 5V. The Arduino Pro 3.3V still works great with our prototyping shield so you can create your own 3.3V shields. The lower system voltage also has its advantages, like ease of use with many common 3.3V sensors.
Arduino Pro does not come with connectors populated so that you can solder in any connector or wire with any orientation you need. We recommend first time Arduino users start with the Uno R3. It's a great board that will get you up and running quickly. The Arduino Pro series is meant for users that understand the limitations of system voltage (3.3V), lack of connectors, and USB off board.
To keep things affordable and low profile, the DC power jack footprint available, but not to populate it. We recommend running the board with a LiPo battery for better portability. Also, to keep the cost low, we made changes like using all SMD components and switching to a two layer PCB.
This board connects directly to the FTDI Basic Breakout board and supports auto-reset. The Arduino Pro also works with the FTDI cable but the FTDI cable does not bring out the DTR pin so the auto-reset feature will not work.
Dimensions: 2.1x2.05" (53.34x52.08mm