Bluno Beetle - The smallest Arduino Board is another milestone in wearable electronics device area based arduino uno, which makes DIY users have more options in the project design. It is fully compatible with Bluno in instructions and procedures, supporting Bluetooth HID and ibeacon modes. 

And it not only supports USB programming, but also wireless programming method. With the V shaped gilded I/O interface, it is convenient to screw conductor wire on it, which could a good choice in the wearable market.

Specification

Bluetooth Chip    CC2540
Sensitivity    (-93dBm)
Working Temperature：    (-10 ℃ ~ +85 ℃ )
Maximun Distance    50m(Open field)
Microcontroller:    ATmega328P
Clock frequency:    16 MHz
Working voltage:    5V DC
Digital Pin    x4
Analog Pin    x4
PWM Output    x2
UART interface    x1
I2C interface    x1
Micro USB interface    x1
Power port    x2

Documents:

Pin Out diagram and info  - https://www.dfrobot.com/wiki/index.php/Bluno_Beetle_SKU:DFR0339#Pinout_Diagram