Wednesday, March 30, 2016

Getting to know the Arduino Uno Board

Getting to know the Arduino Uno Board

In a previous post, Josh thoroughly described the useful and interactive pieces of the Arduino Uno board. This article intends to describe physical components on the board that are not the pins and headers, in order to give new users a "tour" of the Arduino. Many of my explanations will describe components in relation to the locations of other parts. For our purposes, we will orient the Arduino Uno with its power and USB ports on the top and the components out in front of us. And generally, we will travel counter clockwise around the board. First up, the AT328Mega Microcontroller.

Picture of the Arduino Uno - courtesy of
Picture of the Arduino Uno, oriented with the USB and Power ports on the top


The physically largest component on the Uno board is the AT328Mega Microcontroller, which is laid out in a vertical column just to the right of the analog pins, extending from the bottom portion to about two-thirds of the way up the board. This microcontroller is the essentially the "brains" of the Arduino, it is a computer chip that contains the CPU, a small amount of memory, and inputs/output capabilities that are realized by Arduino's analog and digital pins. More information about microcontrollers in general (what they do and how they work) can be found all over the internet, though I quite like's overview which can be found here.


Directly to the right of the AT328, at the very bottom of the board, there is a little 3x2 grid of pins (sort of resembling a bed of needles, or a Braille cel) that poke straight up. The ICSP is used to install a bootloader on your Arduino if it is no longer functioning. As beginners, we won't interact with ICSP but it is a good landmark to orient yourself to the board. More info about Arduino Bootloaders is here.

Moving to the right around the perimeter of the board, you will next encounter the digital pins, which are in a column formation along the right edge. Again, Josh explained these in great detail here. Just to the left of the very top two digital pins is a second ICSP (3x2 grid of pins), oriented perpendicular to the ICSP on the bottom of the board.

Restart Button

In the top right corner of the board adjacent to the USB port and above the digital pins is the restart button, which can be used if your Arduino is behaving erratically, or if you want to restart the program running on the board. Note that it's the only pushable button on the board (it's kind of fun, go ahead and press it).

USB port and AT16megaU2

The USB port is located above the second ICSP and slightly to the left. The Uno takes a standard USB type B cable input, and allows the board to both send / receive information and power from a computer. Just below the USB port is a small square-shaped chip, which is the second microcontroller, the AT16megaU2, which is the "brains" of the Uno's ability to communicated with the computer via USB. That second ICSP is tied to this second microcontroller.

16mhz crystal

Just to the left of the small square shaped AT16mega chip is an elongated oval-shaped cylinder. This is the 16 mhz crystal, which provides a clock input to the microprocessor. Continue to make your way towards the top left corner of the board.

Power Supply

In the top left corner of the Arduino Uno board are all of the components that pertain to power. If you leave your computer connected to the Arduino when using it, this area is of little concern. But if you plan on loading a program onto the Arduino and using the board independently from a computer, you will need to find a way to run power into the device. The power input jack, located in the very top left corner of the board, is a 2.1 mm x 5.5 mm jack than can receive between 7 and 12 VDC. Just to the left of the Power input jack is the voltage regulator, a small rectangular-shaped chip.

Directly below the power jack are two cylindrical capacitors. These capacitors are located between the AT328Mega and the analog pins. We have completed our journey, having traveled counter-clockwise around the entire Arduino Uno Board.

LED Lights

Lastly, it is important to note that there are several LED lights on the Arduino Uno which serve a few different purposes. Diagonally to the right above the AT328 Mega's ICSP is the ON LED light, which lights up green when the unit receives power. Another LED can be found directly to the left of the Digital 13 pin, which is used in the Arduino Blink exercise.

Thank you for reading and if you have any questions or clarification points, please share them in the comments below.


  1. hello,I would like to buy one with 18awg power cord.

  2. Hi there. I like this blog a lot, the descriptions and instructions are awesome! There have been some changes, my board has USB-C, only 1 6-pin male header at the bottom, and the main chip is not 2/3 the size of the board, nothing is. From reading, it's the square chip in the middle-left set like a diamond shape. This puppy has more chips than in your description, or at least differently shaped ones. Any chance you can give us a component description for these? Either way, thank you for this awesome site!!!!!!!!!!