Tiny Electronic Platform for Wearable Products

GEMMA—Wearable Electronic Platform: Arduino-compatible—v2 is a bite-sized tiny wearable platform board in a 1” diameter package. It is powered by an Attiny85 and programmable with an Arduino IDE over USB. This microcontroller board is small enough to fit into any project, and low cost enough to use without hesitation. The new version 2 is physically and code-wise identical to version 1 but has swapped the Mini-B connection for a Micro-B USB connector and incorporates a much-requested on-off switch.

Even though you can program GEMMA using the Arduino IDE, it is not entirely 100% Arduino-compatible.

  • GEMMA does not have a serial port connection for debugging; therefore the serial port monitor will not be able to send/receive data
  • Certain computers’ USB v3 ports do not recognize the GEMMAs bootloader. Just use a USB v2 port or a USB hub in between


  • Easy-to-sew or solder pads for embedding in your wearable project
  • Super small, only 1.1”/28 mm diameter and 0.28”/7 mm thick
  • Low cost enough, you can use one for every weekend project
  • Internal oscillator runs at 8 MHz
  • ATtiny85 on-board, 8 K of flash, 512 bytes of SRAM, 512 bytes of EEPROM
  • Ultra low power, draws only 9 mA while running
  • Micro-USB jack for power and/or USB uploading, you can tape it up or put it in a box and use any USB cable for when you want to reprogram
  • USB bootloader with a nice LED indicator looks just like a USBtinyISP so you can program it with the Arduino IDE (with a few simple config modifications)
  • Bootloader process is robust and foolproof
  • ~5.25 K bytes available for use (2.75 K taken for the bootloader)
  • On-board 3.3 V power regulator with 150 mA output capability and ultra-low dropout. Up to 16 V input, reverse-polarity protection, thermal and current-limit protection.
  • Three GPIO - The three independent IO pins have one analog input and two PWM outputs as well
  • On-board green power LED and red pin #1 LED
  • Power with either USB or external output (such as a battery) - it will automatically switch over
  • Reset button for entering the bootloader or restarting the program
  • Hardware I2C capability for breakout and sensor interfacing