The Arduino Gemma is a miniature wearable device board based on the ATtiny85 microcontroller.

ATtiny85 is Atmel’s 8-bit AVR Risc-based microcontroller with 8kbyte ISP flash memory, 512byte EEPROM and 512byte SRAM.

The MCU achieves a throughput of 20MIPS at 20MHz and operates between 2.7-5.5V.

The board has three digital input/output pins. Two of these can be configured as PWM outputs and the other as an analogue input.

It sells for $10 in the US.

On the board are an 8MHz resonator, a micro USB connector, a JST connector for a 3.7V Li-Ion battery and a reset button.

It can be powered via the USB cable or a battery.