This is a ATmega328 IC in DIP package, pre-loaded with the Arduino Optiboot (Atmega328 16MHz) Bootloader. This will allow you to use Arduino code in your custom embedded project without having to use an actual Arduino board.
To get this chip works, you will need an external 16MHz crystal or resonator, and a 5V power supply to create the minimum Arduino system. If you are not comfortable doing this, we recommend you purchasing the Crowduino board that has all of these built into the board.
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