Power: The Arduino Nano can be powered via the MiniB USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.
Input and output:
Each of the 14 digital pins on the Nano can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pullup resistor (disconnected by default) of 20-50K Ohms. In addition, some pins have specialized functions-