Replacement:DEV-11021. The Arduino Uno has a new R3 version. It breaks out a few more pins, moves the reset button, and uses an ATMega16U2 instead of the 8U2. This page is for reference only.
Arduino is an open-source physical computing platform based on a simple i/o board and a development environment that implements the Processing/Wiring language. Arduino can be used to develop stand-alone interactive objects or can be connected to software on your computer (e.g. Flash, Processing, MaxMSP). The open-source IDE can be downloaded for free (currently for Mac OS X, Windows, and Linux).
This is the new Arduino Uno. In addition to all the features of the previous board, the Uno now uses an ATmega8U2 instead of the FTDI chip. This allows for faster transfer rates, no drivers needed for Linux or Mac (inf file for Windows is needed), and the ability to have the Uno show up as a keyboard, mouse, joystick, etc.
Not sure which Arduino or Arduino-compatible board is right for you? Check out our Arduino Buying Guide! Is the Uno out of stock? We also carry an Arduino Uno SMD variant that should be easier for us to keep in stock.
No reviews yet.
Looking for answers to technical questions?
We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.
Log in or register to post comments.
SparkFun should make a new USB to Serial converter board based on the ATMEGA8u2. It would be cheaper than the FTDI chip and its so much more functional.
Second that. Definitely. Oh Yeah. Awesome. SFE, when/if you start making one, email me.
EDIT: Oops, forgot they had one!
That's all we have for now.
It would have been nice if ardunio had changed the IO pin spacing to standard 0.1" and included an adapter for backward compatibility.
Chris, you should sell your own arduino which has standard pin spacing ;)
This will most likely never happen. Once they made the decision and everyone made shields, they solidified the decision. Don't plan on it changing, ever.
Agreed. That's basically what they said at their New York Maker Faire schpeel when they launched the Uno: "We know it was kinda dumb, but we're sticking with the pin spacing."
It's "Spiel", not "Schpeel".
Why is the pin spacing botched? I don't see any advantage to it.
It was a mistake, not a decision.
I was always under the impression that the pin spacing was off so that shields would only fit one way so what people would have a harder time putting them on backwards.
It's hard to put them backwards, since there are more pins on one side than the other. Also, the header gaps don't line up.
Good or bad, it's a decision (or mistake :) ) that is here to stay, given the huuuge number to shields available now...
Any idea when your getting any more of these? (Not the SMD versions).
Just wondering when these will be back in stock, as im gonna place my order on tuesday when i get payed....
Has the power source switching flaw from the Duemilanove been fixed in the Uno?
I have asked this also but have never got an answer. I have concluded that their is a fundamental problem with these boards and no one wants to admit it.
Pololu also believes there is a flaw in the arduino design and has put a warning on their product page:
I was a fan of the ardunio and figured they would get this problem sorted out quickly and openly, but that did not happen and instead they are having childish debates about the cosmetics of their product. I can not buy another official arduino product now because of this uncertainty.
Can this be solved by putting a diode on the voltage coming from the usb port?
This would block current flow at a cost of 0.5 volts. Most of the chips can run at 3.3 anyway. Not pretty, but workable.
I do not like the idea of putting a non-USB spec device in a design either. I am considering these boards for some robots for our company, but I would have to closely look at the USB power issue. Use one or the other I guess, but not both.
In usb_20.pdf of the USB Spec (http://www.usb.org/developers/docs/):
7.2 Power Distribution
Section: 7.2.1 Classes of Devices
"No device shall supply (source) current on VBUS at its upstream facing port at any time. From VBUS on its
upstream facing port, a device may only draw (sink) current. They may not provide power to the pull-up resistor
on D+/D- unless VBUS is present (see Section 7.1.5). When VBUS is removed, the device must remove power
from the D+/D- pull-up resistor within 10 seconds. On power-up, a device needs to ensure that its upstream
facing port is not driving the bus, so that the device is able to receive the reset signaling. Devices must also
ensure that the maximum operating current drawn by a device is one unit load, until configured. Any device that
draws power from the bus must be able to detect lack of activity on the bus, enter the Suspend state, and reduce
its current consumption from VBUS (refer to Section 7.2.3 and Section 18.104.22.168)."
So as Bongobat described in the link above this means even if the circuit is working as designed it does NOT follow the USB 2.0 specification.
That should very much concern the Arduino folks and Sparkfun.
I really like this product, but this does need to be fixed in future versions.
All the arduinos I have Unos and Duemilanoves all work fine with NO problems what so ever, the powersuply switching works just fine. remember you need 7volts or more on the barrel jack adapter (or vin pin) in order to get the 5volt reg to be 5volts.
I have emailed you directly regarding this issue. Please respond back. We and many others are not able to replicate it.
With a solid 9 volts on the power supply, you get 8.3v at the input to the voltage regulator and 3.7v at the gate of the MOSFET.
However, that is giving 5v at the USB port. To ensure that wasn't a spurious reading due to the high input to the meter, I put a 330 ohm shunt across the meter leads, and I still get 5v.
The NDT2955 is spec'ed to have a minimum Vgs(on) of -2.0v, which works out to a gate voltage of 3v in this application. Thus, it should work fine, but the replacement part clearly isn't.
The extent to which this is an actual problem varies on the application, but clearly this is not good if you're trying to do something that requires USB communication and more power than a USB port can provide.
PS: This was measured on the Duemilanove, but the Uno uses the same circuit.
I just checked my personal e-mail account,the one I am registered here with and I have not received any e-mails from you. Have you sent it though some forum PM that I am unaware of?
However I don't think it is necessary to discuss this privately in e-mails. It is explained in my link that I have purchased the arduino boards through your distributor Pololu and I have already contacted them about the issue and they have tested and confirmed a problem exists in your product. They have taken the correct steps and added a warning to their product page.
If you want to argue the validity of this problem you should contact them as I am sure they will be happy to answer any technical questions you have about this.
My question to you is have you tested the new Arduino Uno under the same conditions outlined in the link above and can promise that they absolutely do not have the same problem?
I also hope that some unbiased forum members that have received their uno will test and report their findings as well.
Once again, send an email to email@example.com. We have sold tens of thousands of these and there is no issue if operated properly (from what we've found). I just don't want to scare people needlessly if there is not a verified issue.
can this new usb functionality allow arduino be recognized as a usb asset that can be shared over LAN such as a webcam/printer? or would that require some more work with socket API for streaming and such?
u can buy a shield the usb host shield witch converts usb to a host so u could add a bluetooth adapter or a wifi usb card and use that along with a web can its 25$ here is the shield http://www.sparkfun.com/products/9947 i hope that helped
The Arduino Uno DEV-09950 is exactly what I've been looking for to enhance my ability to utilize my flight simulator software - http://flightsimulatordownloadd.org/
Ah, goodbye trusty Uno R2, ive had many fun times with you...
I found this a few days ago and have to share it (It is Christmas time!)...
Ever want to make a Data Logger / Data Acquisition System an Arduino?
This free LArVa software from Angstrom Designs makes it too easy!
They also have great documentationto get you going.
It lets you read the 6 Analog channels, read or turn on 12 Digital I/Os… AND drive 6 PWM outputs.
They also offer a great App Note for simple temperature measuring.
I had issues using the Save tab but found right-clicking on the graph, going down to Export let me get the data into Excel and chart it out myself.
Here is a short article about LArVa, written up in Test and Measurement World. (It's not 100% accurate as you can only control/read from 12 digital I/Os, not 14, as you need 2 for the UART to the USB.)
(I don't work for them, I promise. This is just too cool to keep to myself)
""and the ability to have the Uno show up as a keyboard, mouse, joystick, etc.""
that sure is not as easy as you said it. Infact it's very dificult, and should not even be posted there. I have not seen any arduino which has HID inside and HID upload support.
Sorry for the n00b questions, but what exactly comes in the box? The card, a manual and anything else? A breadboard, resistors, LEDs? I don't have anything so I'm thinking I would be better off with a beginners kit? - Q
The Box will include the Uno and a sheet of stickers. The holder in the last picture is sold separately.
Is it possible to remove the Arduino after programming and place it on a breadboard for use?
Yes! That's one of the nice features of the DIP socketed version of the Uno.
uhh, why does the picture have a different power regulator than mine? This one is bigger than mine by a lot...can this one handle more current draw? :/
These boards undergo frequent revisions, but they don't compromise the official specs when updating components. Your part may be smaller but it can handle the same current as the larger part.
which power supply should I buy?
The Arduino can be powered via the USB cable, so if you're going to leave it connected to a PC, you don't need a separate power supply.
If you do want to operate it away from USB, our 9V Wall Supply is a good choice.
I saw the USB capability of this product. Never used an arduino before, but I was wondering if I could use this product with a second USB on a shield to send keystrokes from one USB host to another USB host. I would like to have my mythtv box send channel changing commands to my set top cable decoder box via USB. The set top decoder box accepts a standard USB keyboard as input to change channels. The mythtv box is a linux (fedora 14) box. Both act as hosts on their USB.
Where do i get the usb to connect to my computer?
CAB-00512, in the related products below.
What exactly is the pin spacing for the shields? Is there a dimensioned drawing somewhere? I'd like to throw together some of my own and am feeling -way- too lazy to pull out my calipers at the moment. :)
Nevermind. I think I found it.
I have an inkling that my sda pin on my arduino is not working. I used to be able to get the mpr121 up and running with ease on my arduino, but it no longer sends any data when I press the electrodes. I have tested the voltage and ground pins, however not the irq so that is still a possibility. But when I ran a program to set each analog input as an input for a push button, the push button only got a response on a5 and A0, leading me to believe a4, the sda pin, is no longer working. How can I verify this/fix this?
Wow you guys are selling a $150,000 inventory of Arduino Unos...awesome that the market is that large.
I am new to Arduino, and could not find the following answers. Could someone help...
Question 1. Is this the Arduino Uno (Revision 2) board?
“Revision 2 of the Uno board has a resistor pulling the 8U2 HWB line to ground, making it easier to put into DFU mode.” As quoted from the link: http://arduino.cc/en/Main/ArduinoBoardUno
Question 2. I have older computers that I use for experimental / development purposes, so can the Arduino Uno (Revision 2) board be programmed through a USB 1.1 port on these older computers?
i ve bought an arduino uno i thought i will find the small braedboard in the package like the one in the website foto , but i didn t find it ?
So...you sell the ones made from Italy, not China?
i have got the arduino but it gives a error when i try to upload a file it gives a error i think the avr is dead
which error? Are you sure you have the latest IDE and are selecting 'uno'?
got it to work sorry for being this late in commenting
Just got my first UNO. Really love it but I think it has a problem supplying current. Neither on USB or 12v wall wart can I get an IR led to light with anything greater than a 10 ohm resistor, and it is dim with that though I can send commands using the ir library and everything seems to work.
Are you aware that most of the light emitted by IR Leds cannot be seen by human eyes?
Do any or all Arduino Uno shields also work with the Mega 2560, or must I make my decision as to which to buy based on the shields that are available for each?
how much time dose it take to ship it to india
If you replace the bootloaded chip with an ATMega328 without the bootloader, can you still use the USB connection to load code onto the non-bootloaded chip via some IDE?
Yes, you can.
Search for "arduino bit bang bootloader USB" for links to a Japanese site (geocities.jp) that has the details. (4 wires between USB & ICSP)
This lets you burn a bootloader into the blank chip using a command line program.
Kimio Koaka also wrote a shim program for the Arduino IDE that intercepts the IDE commands for bootloading and modifies them to use the FTDI bit bang USB pins to write the loader.
KK also has some youtube vidoes on the topic.
I'm just wondering... am I able to power this off the 5V rail from a PC's Molex connector? I'm thinking of doing a PC version of the KITT/Cylon/Larson Scanner and I wouldn't want to have a separate power supply for the Uno
Yes you could power this from the 5V rail on the PC. If you have 5V from the PC you can connect it to the GND and 5V points on the power header. The UNO can also be powered through the USB port, so you could mount it inside your computer and just run a USB cable out the back into an extra USB port. Better yet, if your PC motherboard has an extra internal USB port (it would be a male header on the motherboard) you could connect to that. That would let you power and program your UNO without needing to open your PC.
Does anyone know the temperature specs the Arduino can run at? Can I leave it out in a hot area up to 120 F? I can't seem to find this anywhere on the data sheets.
comes with the cable connecting the computer?
when will it be available?my cart is ready. I just wana add this one item and buy my stuff as soon as possible!
not avaliable for backorder? Friday 13....
edit: SMD version is avalible for backorder and normal no. DIP-version arduino uno stopped fabrication?
Bad bootloader in the Uno I received in April 2011... problem had been fixed back in May 2010 per http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1287435600 but I guess the Italians didn't want Unos to be able to load sketches over 30k badly enough to incorporate it.
Various methods of installing a good bootloader are available depending on what additional hardware you have. The method I used is described here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1295516707
Would be good if Sparkfun could let us know when they have stock with updated bootloaders. If my professor hadn't had a spare Duemilanove to reprogram the Uno, I would have been stuck.
1995 in stock. how much time left?
Hmm out of stock... Any ETA on new stock ?
Im happy I got the last Uno in stock, but on the other hand, thanks Sparkfun for sending me a bad board. Turns on, light flashes, but cant upload any sketches. >.
I'm guessing one of the SparkFun employees will come past at some stage and tell you to contact technical support directly.
They will be able to let you know if it's actually a bad board (which aren't that common) and if so arrange a replacement for you.
I have an LED on the board labeled 'L'. Is it supposed to be flashing when plugged into the computer?
It sounds like you have the blink sketch loaded onto your Arduino. Generally that LED only flashes when it is programmed to (if pin 13 is involved, like the example blink sketch), or briefly when uploading code.
The blink sketch is often preloaded onto the Arduino.
I couldn't get it to work with my Macbook using OS X 10.4. This seems to be a problem for others as well. I have confirmed it does work with OS X 10.5. Here's a full description of my problem:
Here's other people with the problem:
Any word on stock? I know these just ran out a couple hours ago - just missed them!
Can always buy the retail version, I suppose?: http://www.sparkfun.com/products/10175
I prefer waiting until less plastic can be used though.
does it ship in the standard arduino paper package with the stickers or simply OEM?
It's in a nice box with stickers. It even has a seal you have to break to open it.
Excellent product! I was able to build keyboard HID firmware for the atmega8u2 and have the UNO behave like a keyboard. It is a bit restrictive with only 4KB available for the firmware so that makes it quite challenging to get the code to fit.
Tips for others wanting to make their own USB firmware to present the UNO as another device:
Grab the Arduino firmware source from git
git clone git://github.com/arduino/Arduino.git
Get version 100807 of LUFA
Unzip LUFA-100807.zip and copy the LUFA subdirectory in it to Arduino/hardware/arduino.
You'll also need avr-gcc and avr-libc installed so you can build the firmware.
You should now be able to cd to Arduino/hardware/arduino/firmwares/arduino-usbserial and build the usbserial firmware by running make. There are guides on the arduino site for using dfu-programmer or flip to load the firmware to your UNO's atmega8u2.
To roll your own firmware, use the arduino-usbserial source code as your starting point and add in code for your target device type (Joystick, mouse, etc) from the LUFA100807/Demos/Device/ClassDriver directory.
A lot more detail on putting together the Keyboard HID firmware, plus source code and firmware hex file here: Arduino Hacking Blog
I've put together Mouse HID firmware and MIDI device firmware for the UNO also, available on my blog.
WOW. +250 units sold in 2 days!
It would appear that I broke something on my board, but the ATmega chip works fine when swapped with someone else's board. Is it possible to buy just a board, without the chip included (because I am cheap...)
Unfortunately not, sorry.
Ah well... It would appear I am going to become a very good Sparkfun customer if this keeps up.
Thanks for the quick response!
OK....this may seem like a stupid question so try to be easy on me :) ..... Im kinda new to arduino, most of my programming has been with PIC. My question is, after developing my prototype with arduino, can I take the Atmega328 out and make a PCB for it? And after that, can I put a new Atmega328 on my arduino? Its just that I dont want to have to buy an arduino for every prototype I make, plus I can design the PCB to take up much less space....sorry if this seems stupid, Im just not sure. Any info would be great...Thanks!! BTW. im using arduino UNO
Thanks for the info! :)
Yes, you can. There are certain board components that are needed to reliably run 'arduino' - but yes, they can be made much small (like http://www.popsci.com/diy/article/2008-04/littlest-arduino - I've seen smaller still, but can't find it at the moment).
The other thing, is that when you buy a replacement Atmega328 you need one of 3 things.
1) Buy it with the Arduino bootloader already installed (SparkFun sells them here: http://www.sparkfun.com/products/9217 )
2) Have a programmer to load the Arduino bootloader
3) Have another Arduino, which can be used to program the bootloader on another one
Hey, I have no knowledge of using an arduino as im new to it as well, but from what i can tell you can buy the chip that is used on the arduino uno and program it....hope this helps
Arduino's must have hit the mainstream..
Mouser had 100+ UNO's three weeks ago and now all gone.
I ordered two from them and got one..
Also ordered one or two from here along with a couple sensors and still waiting. I see the retail and SMD versions are out too.
Glad I'm not in a hurry.
Can anyone please tell me how long it would take if I use USPS first class int. to South Africa?
Try asking over here.
I am in the midst of trouble getting the IDE to upload new sketches to this board. It sounds like the Uno firmware that shipped is (apparently?) broken under Ubuntu 10.10 and causes problems with the serial connection.
These instructions to flash the firmware seem to have worked for a lot of people.:
Maybe it's just my setup though, as I can't even seem to flash the firmware.
This is the reference board, it is a standard size to retain compatibility with shields I'd imagine...
...but there are smaller arduinos:
If you need one of these and it's out of stock, you can get them at Mouser P# 782-A000046, albeit at a slightly greater price.
if they made all the parts smaller, why couldnt they make the board smaller?
then you could not use the shield, If you want a smaller board use the pro mini / mini / fio / lilly pad.
Or even build your own, thats a nice small project to blow 15min
Still out of stock? when will it be in stock again?
I just discovered today that my digital pin 6 does not work on my Uno. Does anyone have any thoughts or similar experience?? Help will be extremely appreciated. Thanks.
EDIT: Nevermind, silly error on my part.
I just got a new arduino uno, and i downloaded the latest software version 0021. when I plug my uno in, my computer tries to install new device. The problem is when I point it to the folder with the drivers (\arduino-0021\drivers\FTDI USB Drivers) it says it is unable to install device. Anyone else have this problem or know of a fix? Any info would be great.
re-read the instructions. You are not installing an FTDI driver. Point it to just the /drivers/ directory instead and it will work.
Thanks! That worked......guess i should read the instructions completely next time......
Yep, as always, RTFMC :-)
still out of stock?!?
When will Arduino Uno be available in stock?
Will these be back in stock in time for the holidays?
Id love to get several of these for gifts but your now sold out of both this version and the retail version.
When will it be back in stock?
What's up with the 16 MHz crystal on these Unos? The picture or the Uno itself doesn't look like it has the standard crystal for the Atmega 328P; was it replaced by a resonator or something similar? (The smaller USB chip seems to have the correct 16 MHz crystal).<br />
I ask because code that I had, working with 57600 baud, doesn't work properly anymore. The bytes are corrupted half or more of the time. I had to switch down to 38400 baud. This suggests the crystal/resonator may be less accurate.
Sorry for the newb question, but I am new to Sparkfun and Arduinos. <br />
When I buy this board, will it come with the necessary cables (USB, power supply, etc)?<br />
The USB will supply the power so no power supply is needed while you are using USB. You will need a A to B USB cable. Like this one http://www.sparkfun.com/products/512
Can I use the following Board with the following soft/hard/ware:<br />
XBee Modules with Xbee Explorer Regulated<br />
In theory, yes. :-)<br />
The Uno is compatible with all the Arduino shields, so it should work just fine.
New to this..Just purchased my 1st Arduino Uno. Do I need a separate power supply or will it be powered via the USB-PC connection
Congratulations! The Arduino can be powered through your USB connection. You do not need a separate power supply as long as it's connected to your computer.
Why is this board (without packaging) $5 more expensive than the same board meant for retailers (with packaging)? It would seem more people would go for the less expensive choice.
Unless they are not the same board and I am mistaken.
They are not the same. We have two retail Arduinos, one is the older board and one is the Uno. The older one is $5 cheaper.
I was sold by the line "ability to have the Uno show up as a keyboard, mouse, joystick, etc." but after some research I have found that it is not possible to do without reprogramming or serious modifications to the board. And I'm seriously considering to return the product. My expectations were not met.
I think Sparkfun folks should update Uno product description.
"Looking at the Uno schematic, they haven't connected up most of the pins from the ATmegaU8 (not even out to pads). So, lots of interesting LUFA stuff won't work without big changes (JTAG, AVR programming, SD cards as mass storage, etc)"
Yes. It's a microcontroller. These require programming. The old Arduino board was not at all capable of this. The functionality is still the same as the old one, it gives you the OPTION of using it as different devices. It is up to you to implement this.
That being said, nothing is possible with the Arduino without coding and programming. It is the very nature of what you're purchasing that dictates this.
Awesome board! Integrates seamlessly with RXTX for JAVA. Drivers installed without a problem using the .INF file from the drivers folder of the Arduino environment installation directory.
If anyone wants to use JAVA to interact with the board, check out the great RXTX tutorial offered here:
Does this board work for sending MIDI out the USB port without some kind of workaround?
Yes it does. Its quite easy to do. I've posted details on my blog along with source code, MIDI USB device firmware for the UNO's atmega8u2, and a sample sketch to send 5 notes to the host PC. Details here: UNO MIDI USB driver.
it can do it but I don't know how much workaround is needed... probably not that much compared with other choices (pics, avrs,etc) :S
I saw people doing this kind of things on the internet over a while, they usually use a joystick hid device (computer see your device as a joystick) and you use some program on the computer to create a hid device based on the joystick controls... so you can play some guitarrig or things like that...
I don't know if that what you had in mind :S
I'm very new at this and I would ask if it comes fully assembled?.
It comes as you see it in the picture, fully assembled.
Hello, i want to know when these will be in stock again?
Aww, we're not product #666 any more.
Well ... a bit disapointed ... When I read on their website few days ago that they were cooking something new, I was hoping for the use of an other UC with more flash/sram capacity... 2k of sram is really short ! currently, I always have to put a lot of data in progmem zone...
I'll try the new MEGA, but it's bigger and I don't need the extra I/Os.
If you want more ram i would recommend using a second or third ATMEGA chip to pass off some of the workload to. Then they can communicate to each other with serial.
For example, if you were programming some light sequence game, you could have one main AVR that could controll the graphics of the game, and everything involved with the lights. Then you could have another one that is controlling the actual game engine, and the inputs from the buttons, switches etc...
This would work for a lot of purposes, and would not be too difficult to set up.
Is there a schematic for the Uno?
is version 20 of the software coming out soon?
there is no uno device listed in the version 19 drop-down menu.
Today, Sept 26th, they are announcing the new hardware changes at Makers Fair. Their home page will have an updated link to the new software within a few days.
Anyone have a positive source that shows this can be recognized as a usb joystick? I have been searching for months for such a device, so would very willingly buy this if the 'as a joystick' claim here is valid.
I would expect so - like the Teensy.
The teensy can send keyboard and mouse signals, sure, but it cannot send analog joystick signals. Iv checked all the source coding for it and while all the parameters are there for usb-serial, usb-keyboard and usb-mouse communication, it has nothing in place for joysticks. I would greatly appreciate any website or documentation you have to the contrary though :) this project is running on almost 8 months now
The DIY FlightSim scene has had USB joystick drivers on AVRs for a while now.
A quick Google search brought up this: http://www.flightsim.com/main/howto/mind.htm which has links to the relevant specs for joystick HID drivers.
Try looking through those and seeing if you can add support for joystick HID masquerading in the ATmega8U2
I followed Moggie100's link to the Flightsim.com USB HID implementation - which is based on http://www.cesko.host.sk/ firmware. Interesting, but too much time & effort for me to adapt to Arduino ... if the Arduino is even capable of it.
I came across a product called U-HID - unfortunately not Arduino-based - if all you need is a configurable USB HID device http://www.u-hid.com/home/uhid_nano.php. Looks like a good candidate for custom game controllers, or in my case to adapt an old CH FlightSim Yoke from 15-pin to USB.
Have any other specs changed or aside from the uprate USB interface and the graphics, this is the same as the previous version?
It would appear that nothing else has changed, but I could be mistaken.
from the datasheets at http://www.atmel.com/dyn/products/product_card.asp?part_id=4600 and http://www.atmel.com/dyn/resources/prod_documents/doc7799.pdf
the ATmega8U2 appears to be a full AVR cpu with built-in usb 2.0 interface
depending on what firmware gets loaded into the ATmega8U2, it could act as ANY usb device, it feels like serial/keyboard/mouse are options in the current firmware and you select them somehow over the serial link between the 2 avr's
why the AVR MCU and not a simple FTDI USB-to-Serial chip ?
with this kind of configuration, the computer can see your board like anything, not only a serial port device, and that gives a bunch of cool stuff that can be made with arduino... just a bunch of new possibilities...
Does is in default work as a Serial Device because I don't need that feature for now ?
The other features of the ATmega8U2 chip would require it to be reprogrammed. If you completely reprogrammed the ATmega8U2 without providing the serial interface code it would cease to function as a serial interface.
Out of the box it will work the same as the old Arduino.
Uhhh, you'll connect it to your computer the same way, etc. everything is the same with the Uno, except you can use it as a keyboard, mouse, joystick, or anything. TTL still exists on the chip, the RX and TX pins break it out.
whoo hoo anyone know how to eneble the hid functions of the serial converter