This article list the differences that are in the previous Arduino UNO boards & the currently available Arduino UNO board, i.e., REV 3.

Hope you will find this Comparision interesting!

USB Chip Position

"ATMEGA8U2" is positioned at 45 degrees in the 2nd board (Arduino UNO Rev 2). Changed back to 90 degree on the Revision 3 board.

USB Chip ( ATMEGA8U2) Alignment Comparison

Solder Pads

ATMEGA8U2".

Solder Pad Similarities Between Rev 2 & 3 Both Rev 2 & 3 boards add 4 solder pads (JP2) connecting to pins PB4 to PB7 of the "".

IC Number

The Arduino Uno and Arduino Uno Revision 2 both have an ATMEGA8U2 USB microcontroller onboard but this is upgraded to an ATMEGA16U2 on the Rev 3 board.





Reset Circuit

REV 3 adds a diode parallel to the USB ATMEGA16U2 reset pin pull-up resistor, which was not in the previous 2 Arduino UNOs.



A diode parallel to the USB ATMEGA16U2 reset pin pull-up resistor

ICSP Header

Rev 2 & 3 boards are both supplied with header pins in the USB ATMEGA ICSP header rather than just solder pads in the Arduino Uno (initial version).





Rev 2 & 3 boards are both supplied with header pins in the USB ATMEGA ICSP header rather than just solder pads in the Arduino Uno (initial version).

Pin Connectors

The REV3 board have changes from the 8 pin connector to 10 Arduino pin connector, containing digital pins numbering 8 to 13, GND and AREF for a 10 pin connector. There are the 2 analog input pins als that can be used for I2C.

Revision 3 boards also change the 6 pin connector that has the reset pin to an 8 pin connector.

One of the new pins on this header is the IOREF that allows shields connected to the board to adapt to the voltage required. One more pin is reserved for future use.



Differences Between Arduino UNO, R2 & R3 Pin Headers