Arduino uno R3 rev3, Size: 53.4mm 75mm, The main chip: ATMEGA328 microcontroller, USB line power supply: 5v, The external power supply: 7-12v, recommended 9v, The digital input / output pins 14 (including 6 supports PWM), The analog input range 6. 6 Pin, Built-in flash memory: 32K, SRAM: 2k, EEPROM: 1K, Clock Frequency: 16MH Arduino UNO R3 is the 2012 launch of an easy-to-open-source controller, compared with the Arduino UNO and no major changes hardware, the biggest difference is that the USB to serial circuit, instead of a piece of ATMega16U2 microcontroller, whereby costs also improved, the software part before, there is no big change. Change Pin: next AREF pin plus two I2C pins (SDA and SCL, just Analog copy 4 and 5, not additional I2C interface), in addition, in the next RESET also added two pins, one IOREF, can Let adapt onboard expansion board voltage, this pin expansion board just told what voltage the current board (such as UNO is 5V, copy can be seen as the power pins and does not provide power to pull level on), and the other is inactive after placeholder pins. More stable RESET circuit. RESET key position has changed, has been moved close to the USB interface board corner, easier press. ATmega16U2 instead 8U2, this does not mean that there is 16K flash of R3 let your code run faster, this update is a USB interface chip service, in theory, it allows UNO can simulate USB HID, such as MIDI / Joystick / Keyboard.