However, while the 5V version runs at the same speed and voltage, the 3V version uses 3V logic and 12MHz clock which means it's good when you want a lower-power and lower-voltage setup. The Pro Trinket uses the Atmega328P chip, which is the same core chip in the Arduino UNO/Duemilanove/Mini/etc.

So it's great once you've finished up a prototype on an official Arduino UNO and want to make the project smaller. The Pro Trinket PCB measures only 1.5' x 0.7' x 0.2' (without headers) but packs the same capability as an Arduino UNO. Adafruit also added Optiboot support, so you can either program your Pro Trinket over USB or with a FTDI cable just like the Pro Mini and friends. Like the Trinket, it has onboard USB bootloading support - Adafruit opted for a MicroUSB jack this time. That's why Adafruit designed Pro Trinket, with 18 GPIO, 2 extra analog inputs, 28K of flash, and 2K of RAM. Trinket's a year old now, and while its been great to see tons of tiny projects, sometimes you just need more pins, more FLASH, and more RAM.

It's like an Arduino Pro Mini with more pins and USB tossed in.

Pro Trinket combines everything you love about Trinket with the familiarity of the core Arduino chip, the ATmega328. Trinket's got a big sister in town - the Pro Trinket!

Adafruit trinket 5v wiring