This clever HAT from DFRobot adds an Arduino (ATmega32u4) on top of your Raspberry Pi, giving you the very best of both worlds for your projects!
The HAT has broken out pins from both your Raspberry Pi GPIO and the onboard ATmega32u4, alongside an XBee socket (with Pi serial/Arduino serial switch), RTC reset button (Arduino), SDA/SCL breakouts.
A bidirectional logic converter has been included, which converts your Raspberry Pi GPIO signal voltage between 3.3V and 5V allowing compatibility with hundreds of sensors.