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, we've chosen to make 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. In this latest version of the Arduino Pro we've also moved the FTDI headers back just a skoach so that the pins don't hang over the edge of the board. We've also populated it with a sturdier power selection switch.

Note: A portion of this sale is given back to Arduino LLC to help fund continued development of new tools and new IDE features.

 

Features:

• ATmega328 running at 8MHz external resonator
• Low-voltage board needs no interfacing circuitry to popular 3.3V devices and modules (GPS, Accelerometers, sensors, etc)
• USB connection off board
• 3.3V regulator
• Max 150mA output
• Over current protected
• Reverse polarity protected
• DC input 3.3V up to 12V
• Resettable fuse prevents damage to board in case of short
• Power select switch acts as on/off switch

Dimensions: 2.1x2.05" (53.34x52.08mm)

Documents:

• Schematic
• Eagle Files
• Arduino Pro Homepage
• Getting Started