This tiny wearable dev board designed by Aprilbrother measures only 31mm in diameter but it gives you compatibility with the Arduino IDE and Bluetooth Low Energy (BLE) to play with. The microcontroller at the heart of this board is the ATmega32U4 which comes pre-programmed with a USB boot-loader meaning you can plug it straight into your computer and get programming, without the need for a USB-serial adapter.
A JST connector is included on the board for plugging in a single cell 3.7V lipo battery. The board can also be powered from the USB port but unfortunately you cannot charge the battery from USB power. Perhaps this was a necessary trade off to keep the board size to a minimum, it’s just something to keep in mind when designing your project.
Aprilbrother has done a great job on documentation with hookup tutorials and schematics all available over on the BLEPad wiki page. There are 12 GPIO pins and 4 ADC pins on the board. Combine that with BLE and there are a whole host of cool projects that could come out of this, especially if you connect it to a smartphone!
