Arduino Gemma is a miniature wearable microcontroller board based on the ATtiny85. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a battery to get started on your wearable projects!
Overview
Technical specs
| Microcontroller | ATtiny85 |
| Operating Voltage | 3.3V |
| Input Voltage | 4V-16V |
| Digital I/O Pins | 3 |
| PWM Channels | 2 |
| Analog Input Channels | 1 |
| DC Current per I/O Pin | 20 mA |
| Absorption | 9 mA while running |
| Flash Memory | 8 kB (ATtiny85) of which 2.75 kB used by bootloader |
| SRAM | 512 Bytes (ATtiny85) |
| EEPROM | 512 Bytes (ATtiny85) |
| Clock Speed | 8 MHz |
| Diameter | 27.94 mm |
Documentation
The Arduino Gemma can be powered via the micro USB connection or with a 3.7V Li-Ion battery (connected to the JST connector on the board). Either power source is regulated down to the operating voltage (3.3V) by the on-board MIC5225.
- Vout: This is a voltage OUTPUT pin, it will be connected to either the USB power or the battery input, whichever has the higher voltage. This output does not connect to the regulator so you can draw as much current as your USB port / Battery can provide (in general, thats about 500mA).
- 3Vo: This is the 3.3V OUTPUT pad from the voltage regulator. It can provide up to 150mA at a steady 3.3V. Good for sensors or small LEDs or other 3V devices.
- GND: Is the common ground pin, used for logic and power. It is connected to the USB ground and the power regulator, etc. This is the pin you’ll want to use for any and all ground connections
The ATtiny85 has 8 kB (with 2.75 kB used for the bootloader). It also has 512 Bytes of SRAM and 512 Bytes of EEPROM (which can be read and written with the EEPROM library).
Each of the 3 digital I/O pins on the Arduino Gemma can be used as an input or output, usingpinMode(), digitalWrite(), and digitalRead() functions. They operate at 3.3V volts. Each pin can provide or receive a maximum of 20 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms.
- TWI: D0 (SDA) and D1 (SCL). Support a simple TWI communication using the Tiny Wire library.
- PWM: D0, D1 Provide 8-bit PWM output with the analogWrite() function. The Gemma doesn’t have a 16bit timer, so to drive servos the Soft Servo library is suggested.
- LED: 1. There is a built-in LED connected to digital pin 1. When the pin is HIGH value, the LED is on, when the pin is LOW, it’s off.
- Analog Input: A1 The Arduino Gemma has 1 analog input, labeled A1, which can also be used as digital I/O. The analog input provide 10 bits of resolution (i.e. 1024 different values). By default the analog input measure from ground to 3.3 volts.
The Arduino Gemma doesn’t support the Serial Monitor, but SoftwareSerial library allows serial communication on any of the Gemma’s digital pins.
The Arduino Gemma can be programmed with the Arduino Arduino Software (IDE).
Note: Some computers’ USB v3 ports don’t recognize the Gemma’s bootloader. Simply use a USB v2 port or a USB Hub in between.
The Arduino Gemma requires a physical press of the reset button before an upload. After the processor resets, the bootloader starts, remaining active for about 10 seconds.
The Arduino Gemma is a circle, approximately 27.98mm (1.1″) round in diameter. The Micro USB connector extends slightly beyond this diameter. The board itself is .8mm (1/32″) thick (approximately 6.5mm (1/4″) including components, the tallest of which is the JST battery connector).