Adafruit Pro Trinket - 3V 12MHz

Say hello to Adafruit's newest addition to the Trinket lineup, the Pro Trinket! Not only does is support the much loved ATmega328P, but also has a custom bootloader that gives you a handy USB interface.

The Trinket Pro has a total of 18 GPIO, 2 extra analog inputs, 28K of flash, and 2K of RAM. With all this capability packed into a form factor of only 1.5" x 0.7" x 0.2" (without headers), you will be surprised how easy it is to migrate your project from an Uno down to the tiny Pro Trinket.

Keep in mind that because of the Pro Trinkets USB bootloader, the flash storage (Arduino sketch size) is reduced to 28K instead of the Uno's 31.5K. This should only be a problem if your pushing the absolute limit of the Uno's flash memory when you got to make the switch over to the Pro Trinket.

Note: 

The 3V Pro Trinket runs at 12MHz which differs from the 16MHz of the Pro Trinket 5V and Arduino Uno. While this shouldn't affect most libraries, it may have an impact on libraries which are timing critical. Make sure to read the documentation on the libraries you wish to use before selecting the Pro Trinket 3V.

Here's some things you may have to consider when adapting Arduino sketches:

• Pins #2 and #7 are not available (they are exclusively for USB)
• The onboard power supply is a 3.3V regulator and it can provide 150mA output
• You cannot plug shields directly into the Pro Trinket
• There is no Serial-to-USB chip onboard. This is to keep the Pro Trinket small and inexpensive; you can use any FTDI cable to connect to the FTDI port for a Serial connection. The USB connection is for uploading new code only.
• The bootloader on the Pro Trinket use 4KB of FLASH so the maximum sketch size is 28,672 bytes. The bootloader does not affect RAM usage.

Here's some handy specifications:

• ATmega328P onboard chip in QFN package running at 3.3V logic
• 12MHz clock rate, 28K FLASH available
• USB bootloader with a nice LED indicator looks just like a USBtinyISP so you can program it with AVRdude and/or the Arduino IDE (with a few simple config modifications).
• Also has headers for an FTDI port for reprogramming
•  Micro-USB jack for power and/or USB uploading, you can put it in a box or tape it up and use any USB cable for when you want to reprogram.
•  On-board 3.3V power regulator with 150mA output capability and ultra-low dropout. Up to 16V input, reverse-polarity protection,   thermal and current-limit protection.
• Power with either USB or external output (such as a battery) - it'll automatically switch over
• On-board green power LED and red pin #13 LED
• Reset button for entering the bootloader or restarting the program.
• Works with 99% of existing Arduino sketches (anything that doesn't use more than 28K, and doesn't require pins #2 and #7)
• Mounting holes! Yeah!