The Pro Trinket 5V 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 much of the same capability as an Arduino UNO. Also added is 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 - they 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, so delicious. Trinket's got a big sister in town - the Pro Trinket 5V! Pro Trinket combines everything you love about Trinket with the familiarity of the common core Arduino chip, the ATmega328.

So while we still carry the Pro Trinket so that people can maintain some older projets, we no longer recommend it. Deprecation Warning: The Pro Trinket bit-bang USB technique it uses doesn't work as well as it did in 2014, many modern computers won't work well.

Adafruit trinket 5v keyboard