1. UNO R3 development board is compatible with original Arduino DIY. 2. It has perfect quality and performance. 3. More pins: 2 more I2C pins are added by the side of AREF pin (SDA and SCL, copies of Analog 4 and 5, not extra I2C interfaces); Moreover, two other pins are also added by the side of RESET. One is IOREF, which enables the expansion board to adapt to the on-board voltage. And the other is a stand-by occupied pin. 4. More stable RESET circuit: The RESET has been moved to the board corner, near to the USB interface, which is more convenient to use. 5. 5V USB powered. 6. Built-in flash memory: 32K. 7. External power source: 7 - 12V, 9V recommended. 8. Clock frequency: 16MHz.
