Adafruit GEMMA v2 - Miniature Wearable Electronic Platform is a tiny wearable platform board with a lot of might in a 1" diameter package. Adafruit GEMMA v2 is powered by an Attiny85 and programmable with an Arduino IDE over USB. By using this board you'll be able to realize any wearable project.
Adafruit GEMMA v2 is developed by Adafruit who wanted to design a microcontroller board that was small enough to fit into any project, and low cost enough to use without hesitation. Adafruit GEMMA v2 is perfect for projects that are simple and small. It is one of the lowest cost sewable controller.
Adafruit GEMMA v2 is the second version of the microcontroller board Arduino GEMMA which is developed by Adafruit and Arduino together. On March 4, 2015 Adafruit released Adafruit GEMMA v2 which is physically and code-wise identical to the first version Arduino GEMMA. In Adafruit GEMMA v2 the USB connector is changed from Mini-B to Micro-B and an an on-off switch is added as requested by the community.
Attiny85 is a great processor because despite being so small, it has 8K of flash, and 5 I/O pins, including analog inputs and PWM “analog” outputs. The board has a USB bootloader so you can plug it into any computer and reprogram it over a USB port just like an Arduino (it uses 2 of the 5 I/O pins, leaving you with 3). Adafruit even made some simple modifications to the Arduino IDE so that it works like a mini-Flora. Adafruit GEMMA v2 - Miniature Wearable Electronic Platform is perfect for small and simple projects and very useful in wearable electronics projects.
Even though you can program Adafruit GEMMA v2 using the Arduino IDE, it's not a fully 100% Arduino-compatible. There are some things you trade off for such a small and low cost microcontroller. Adafruit GEMMA v2 does not have a serial port connection for debugging, so the serial port monitor will not be able to send/receive data and USB v3 ports of some computers don't recognize the GEMMAs bootloader. Simply use a USB v2 port or a USB hub in between.
Adafruit Web Site: https://www.adafruit.com/products/1222