1.※UNO R3 is an easytouse open source controller. There is no major change in hardware compared to UNO. The big difference is that the USB to serial port circuit part is used instead of an ATMega16U2 microcontroller. The software part is the same as before, without major changes. 2.※Pin changes: Two I2C pins are added next to the AREF pin (SDA and SCL are only copies of Analog 4 and 5, not additional I2C interfaces). In addition, two pins are added next to the RESET. One is IOREF, which can enable the expansion board to adapt to the onboard voltage. This pin only tells the expansion board what the current onboard voltage is (for example, UNO is 5V, which can be regarded as a copy of the power pin, and does not provide a level pullup), and the other is the placeholder pin that will be used in the future. 3.※More stable RESET circuit. The position of the RESET key has also changed and has been moved to the corner of the board close to the USB interface, making it more convenient to press. 4.※ATmega16U2 replaces 8U2, which does not mean that 16Kflash R3 can make your code run faster. This update serves USB interface chips. In theory, it allows UNO to simulate USB HIDs, such as MIDl/Joystick/Keyboard.