Femtoduino: an ultrasmall (20.7x15.2 mm) libre Arduino compatible board

First picture of Femtoduino

Femtoduino is an ultrasmall (20.7x15.2 mm) libre Arduino compatible board.

By using the QFN32 version of the ATMEGA 328p, 0.05" connectors, 0402 components and removing everything not strictly necessary, I've been able to design and hand build an Arduino compatible board which is very small (20.7x15.2 mm) and ultra light (2g) but has exactly the same computing power of the Arduino Duemilanove or UNO.

Femtoduino has been developed for ultrasmall Arduino prototyping. I had the need to add "Arduino intelligence" to quite small objects (balls, cubes, mices, etc) so I needed to shrink down the size of Arduino as much as possible. Femtoduino is the result.

For regular prototyping, Femtoduino comes with a handy breakout board which breaks out Femtoduino's 0.05" connectors into regular 0.1" pins so that you can use it on standard breadboards or perfboards.

Femtoduino is a true libre hardware project. It's designs are released under CC-BY-SA 3.0 Unported and it has been designed using Kicad, a libre PCB design software.

Femtoduino schematics are based on the Arduino Pro Mini by Sparkfun Electronics and Arduino Mini by Team Arduino.

Video presentation of Femtoduino

Femtoduino Sources and Schematics

Below you find all the sources needed to build your own Femtoduino:

You can get the most updated sources from my personal repository using bzr with the following command:

bzr co http://repository.varesano.net/Femtoduino

Please support the project!

Femtoduino is a true libre hardware project. I released it under a libre licence to allow people to build their own and to give my contribution to the Arduino community.

However, I spent a lot of time designing Femtoduino, so if you are going to use its designs for your own projects or if you plan to sell clones of Femtoduino I'd really appreciate if you could donate me some money to support further versions of Femtoduino or my other libre hardware projects.

Donations can be made using Paypal to my account: fvaresano [at] yahoo [dot] it
Alternatively you cneveran use the donate button on the right sidebar of the page.

Even a couple of dollar/euro helps! Thank you.

Suggestions? Comments?

Please leave a comment below. Thank you.

USB connector for femtoduino

Submitted by Anonymous (not verified) on Thu, 2014-06-12 10:40.

Which USB connector IC do we use in femtoduino?
It is not mentioned in bill of materials

Buy Femtoduino

Submitted by Skip (not verified) on Thu, 2014-05-22 06:43.

Where can i buy a femtoduino???
Pease help me

Voltage in

Submitted by Jeff Clayton (not verified) on Fri, 2013-05-24 02:43.

Hello All, First off, thank you for the Femtoduino, i love it to death!!!! can it be run off a small 3.7V LiPo? if so, any idea on processor speed?

Femtoduino on 1S Lipo 3,7V

Submitted by Èric (not verified) on Tue, 2013-07-23 15:58.

Hi Jeff,
Youtube Link: http://www.youtube.com/watch?v=r1pavL3uvTw
A super small 18g Tricopter with Femtoduino.
Clock Speed 16 MHz and it runs on a 1s Lipo easily.
Best Regards, Èric

Femto(duino) 20g Tri Copter on 1S Lipo 3,7V

Submitted by Èric (not verified) on Fri, 2013-08-23 14:01.

Hi Jeff,
Femto(duino) Tricopter 20g, PID Tuning: http://youtu.be/JbXyk6UADBs
Femto(duino) Tricopter 20g, Outdoor Flight: http://youtu.be/oacVziO6ie4
Regards, Èric

Do you have the Femtoduino Breakout Board in Eagle format?

Submitted by Salman Sheikh (not verified) on Mon, 2013-03-11 23:09.

I was wondering if you do...


Submitted by Marino (not verified) on Thu, 2013-02-07 18:06.

I need a tiny microcontroller like femtoduino but with bluetooth connectivity. Any idea for a small size bluetooth module for femtoduino?
Best regards,

Femtoduino and Bluetooth

Submitted by Èric (not verified) on Sat, 2013-08-24 07:58.

Hi Mario,
that would be something for you:

Uploading sketch over Bluetooth:

Regards, Èric

Thank you Eric

Submitted by Marino (not verified) on Sat, 2013-08-24 12:17.

I will check it soon.
Best Regards,

I'm working on making a

Submitted by Anonymous (not verified) on Sun, 2013-02-17 05:29.

I'm working on making a bluetooth breakout for this arduino, will post on my site hopefully in the next few weeks. you can contact me if you're interested

Bluetooth for Femtoduino?

Submitted by Anonymous (not verified) on Thu, 2013-10-03 21:57.

I saw that you had posted a while back that you were working on a bluetooth device for Femtoduino--is there any other info on this?



Happy to know about it! Let's

Submitted by Marino (not verified) on Sun, 2013-02-17 13:48.

Happy to know about it! Let's see!!!

Good outfit for assembly

Submitted by Ron K. Jeffries (not verified) on Wed, 2012-09-26 18:32.

I recently rec'd an email from someone asking where I had my Femtoduino boards assembled. Here is the info (I misplaced the email, sorry!)

http://vareda.com/ in Goleta (near Santa Barbara, CA USA

Great small shop, high quality, reasonable prices.

Great work!

Submitted by Charalampos (not verified) on Thu, 2012-03-22 14:06.

Hello, fantastic work! Just wanted to let you know that you have been featured in http://www.buildinginternetofthings.com/blog/

I think that such contributions to the Open Hardware community can facilitate the establishment of Internet/Web of Things must faster!

Kind regards,
Charalampos Doukas

Buy Femtoduinos at Femtoduino.com

Submitted by Alex Albino (not verified) on Sat, 2012-03-03 09:01.

Ok, the site is up and running. If you would like to pre-order a few of these as pre-made femtoduinos, fill out the form at http://www.femtoduino.com

The boards will be manufactored by SFCircuits (in San Francisco, CA)



Submitted by Ralph Zoontjens (not verified) on Sun, 2011-11-13 18:59.

For a project I am currently working on we need a very small prototyping board, and this one looks perfect. Unfortunately I do not have the expertise and the time to make these myself. Do you sell the Femtoduinos, or is there anywhere I can buy something similar that you know of?


Femtoduino boards for sale

Submitted by Alex Albino (not verified) on Tue, 2012-02-28 03:12.

You can buy them pre-assembled at http://www.femtoduino.com

The shop will be live by March 30 2012, or before.

Do you sell the Femtoduino?

Submitted by Ralph Zoontjens (not verified) on Sun, 2011-11-13 18:58.

For a project I am currently working on we need a very small prototyping board, and this one looks perfect. Unfortunately I do not have the expertise and the time to make these myself. Do you sell the Femtoduinos, or is there anywhere I can buy something similar that you know of?


I have a couple of Femtoduinos

Submitted by ron k jeffries (not verified) on Sun, 2011-11-13 19:20.

I had a small run of Femtoduinos assembled, as I did not
have the expertise.

That project has been sidelined for quite some time.

These are assembled boards, but do not have a bootloader
installed and thus have not been tested.

If you feel you can handle the remaining steps I'll
send to you at no charge via US Mail (in the USA).

Or you may want to find someone who will load the bootloader
and make sure the LEDs blink first.

rjeffries [at] gmail [dot] com

Omar Khayyam wrote:

The Moving Finger writes; and, having writ,
Moves on: nor all thy Piety nor Wit,
Shall lure it back to cancel half a Line,
Nor all thy Tears wash out a Word of it.

ron k jeffries

ronkjeffries on G+
@ronkjeffries on Twitter

Femtos are all gone, gone gone.

Submitted by Ron K Jeffries (not verified) on Fri, 2012-02-24 00:16.

The PCBs and kits I bought were assembled, and various and sundry
people have them. At least one person told me his Femto worked.

Requests continue to dribble in. If someone were to order a run of PCBs from Laen, and order the kits. I know a place that does assembly
at a reasonable price.

Thanks for all the fish. I figure I lost (invested?)
less that $100 in this learning experience. I ended up giving
them away because they had not been tested.

Congratulations on the Hack a

Submitted by Williwaw (not verified) on Sun, 2011-10-02 14:52.

Congratulations on the Hack a Day feature. Keep up the good work and thank you for your open source hardware.

Another Board

Submitted by Brian (not verified) on Thu, 2011-09-15 20:36.

From Pittsburgh, PA USA

Fabio Veresano - Thanks for your work and sharing.
Steve B. - Thanks for making the bare board.

The SMD soldering education and experience for reflow by hand and hacking a skillet was intense. Our stock skillet did not get hot enough so our 1st board, pictured below, was hand soldered by one of my sons (13yr. old). The next board will be reflowed on a hacked skillet.

The reward: A functioning tiny, tiny Arduino Clone ---> Femtoduino!

Note: In the picture - the bright RED LED is --- FLASHING! LOL :-)

F.Varasano Femtoduino in Pittsburgh, USA

Awesome! Congratulations!

Submitted by fabio on Thu, 2011-09-15 20:37.

Awesome! Congratulations!

In the future, you may wanna evaluate buying an hot air reflow gun.. you'll find very cheap ones on ebay which will work great to start.

Dead Pins & DTR?

Submitted by Brian (not verified) on Fri, 2011-09-16 18:16.

To those who read about and build THE Femtoduino - Has anyone had dead pins on the Atmega chip?

I've 5 pins that are dead on the board. They are actually with no output at the chip. I've used Fabio's test script of blinking LEDs to find the bad pins. One pin is a bad solder joint on the chip but, the other four pins (A6, A7, D5, & D6) do not have any output at the chip's connect pins.

And a design question: What is the DTR pin on the board? To which Atmega pin does it map? Is it simply connected to the RST with an included cap as shown on the Femtoduino schematic?

Lastly - below is a pinout sketch of the Atmega328P-MU for any with interest.

I don't think that there is

Submitted by fabio on Fri, 2011-09-16 19:05.

I don't think that there is any design flaw which makes those four pins unusable.. I guess it may be just some problem with your soldering or chip or PCB.

The DTR chip doesn't connect to anything but just to the capacitor as shown in the schematics. That's how Sparkfun implemented the reset in their Arduino Pro Minis and that's what I did here. The fact that you programmed this with the Arduino Duemilanove, makes the DTR chip pin useless.


Submitted by Brian (not verified) on Fri, 2011-09-16 19:40.

Note: To auto-reset the board via program just use the RST point on the board which is connected to the PC6 pin on the Atmega chip. It this connection is grounded or brought Low the chip/board will reset.

Programming the board with sketches works very well with a Duemilanove bootloader and Arduino-0022 IDE. I use the following connection scheme with a Modern Device USB Bub (use Bubs I or II):

Femtoduino Connections: Vin, Gnd, TX, RX, RST.
USB-Bub or similar: 5V, Gnd, RX, TX, DTR. Match in order of the previous.

To load the bootloader I read Fabio is using a USBasp. I tried it. The USBasp works very well.

So far things Work Great!

Clarification re programming the Femto

Submitted by ron k jeffries (not verified) on Fri, 2011-09-16 22:59.

Is this summary correct?

Starting with assmebled Femtoduino that does not have bootloader,

1) need USBasp to load bootloader

Once Femtoduino has bootloader,

2)need BUB-II to send Arduino sketches from the USB port of my laptop

[1] http://www.protostack.com/accessories/usbasp-avr-programmer
also available in Europe from the inventor. ;)

[2] http://shop.moderndevice.com/products/bub_ii

I assume there are many other ways to proceed, I simply need to know
what to buy so I can move forward.

for what it is worth, I also own an Arduino Uno.

As you can tell, I am a newbie. May 1,000 flowers bloom.
If (I mean WHEN) I eventually get these operational,
I may or may not make some more.

ron k jeffries
rjeffries [at] gmail [dot] com
805 567 4670

To program the Femtoduino, I

Submitted by fabio on Sat, 2011-09-17 22:15.

To program the Femtoduino, I also have been successful with ArduinoISP (only with Arduino Duemilanove on Windows) however the USBasp is easier and more flexible.

Regarding USB connection, any FTDI breakout board will work. There are many vendors for this.

Go for it....

Submitted by Brian (not verified) on Sat, 2011-09-17 20:14.

Go for it....

GREAT Design!

Submitted by Brian (not verified) on Fri, 2011-09-16 19:18.

Fabio - I did not think or imply a flaw in your design. I was asking about a bad Atmega chip. I know the soldering is suspect as I'd noted on pin D2. I was also thinking that maybe the fuse settings I'd used were making those pins not function for the test. Sorry, if you thought I meant there was a flaw.

--- You state, "The fact that you programmed this with the Arduino Duemilanove, makes the DTR chip useless." What other bootloader and use would make the DTR useful? And did you mean to write 'DTR chip'? I'm confused.



Sorry, typo.. fixed.

Submitted by fabio on Fri, 2011-09-16 20:17.

Sorry, typo.. fixed.


Submitted by Brian (not verified) on Fri, 2011-09-16 19:23.

The definitions of terms in my usage should be but, I may confuse them anyway -

Chip - Atmega328P-MU
Board - Femtoduino
Pin(s) - Connection Leads on the Atmega328P-MU

Someone opened an IndieGoGo

Submitted by fabio on Wed, 2011-09-14 13:01.

Someone opened an IndieGoGo founding for producing Femtoduinos boards. I'm not behind that found rising but I think people willing to have Femtoduinos available for sale may wanna support the founding. Here is the link http://www.indiegogo.com/Femtoduino-production-smallest-Arduino-compatib...

my compliments very nice and very smoll

Submitted by claudio (not verified) on Mon, 2011-09-05 12:10.

I ave see Femtoduino i like the borad is available to purchasing
about the cost for 5 peices where have to purchase?
again my compliments very ultrasmoll.

You may wanna get in touch

Submitted by fabio on Mon, 2011-09-05 12:32.

You may wanna get in touch with some of the people below. They may have spare Femtos for you.

Personally, I don't have any right now.

Update plus breakout board question

Submitted by ron k jeffries (not verified) on Mon, 2011-08-29 06:39.

1) I have five assembled Femtoduinos. Have not programmed any yet.
I do have a working Arduino Uno, but will have to
figure out the next steps. In good time, I assume.

2) the breakout board for Femtoduino looks handy. Has anyone
sent it out to have PCBs made? Or has it only been DIY PCB fabbed?
How is does Femtoduino connect to the breakout board?

3) I finally have KiCad working and am looking at the Breakout board

.brd file I have a LOT to learn to figure out how to generate gerbers if I want to get some PCBs made by Laen.

If anyone is intereste din a couple of Femtoduinos. email me rjeffries [at] gmail [dot] com


1) I programmed my Femtos

Submitted by fabio on Mon, 2011-08-29 09:38.

1) I programmed my Femtos using the Arduino Duemilanove with the ArduinoISP technique. Last time I checked, the ArduinoISP wasn't working with the Arduino UNO. Lately I switched to the USBAsp programmer, which is working pretty good.

2) I used Laen services to have some Femtoduino bob fabricated. You can use female/male headers to connect to the bob. However, I don't suggest you using the bob at all.. standard rigid wires will plug into the femto pretty nicely.

3) From Kicad pcbnew, File->Plot, Gerbers and drill files. Choose all the layers. You can also just use the BOB Gerbers already linked in the article above.


Submitted by Brian (not verified) on Wed, 2011-09-14 19:47.


Which bootloader do you use for the Femtoduino?

Your Bootloader

Submitted by Brian (not verified) on Wed, 2011-09-14 21:51.

Nevermind ---- I should have read the forum again.

On 2011/2/22 Fabio said, "I used the bootloader of the Arduino Duemilanove on the 5V 16MHz version of Femtoduino. I still did not built a 3.3V 8MHz Femtoduino but I guess that the bootloader for the Arduino Pro Mini 3V 8MHz should work just fine."

10K Resistors

Submitted by Brian (not verified) on Wed, 2011-08-24 22:47.

Hi - I've read the forum and bought the BOM listed from Mouser. The posted list seems to be short one 10K resistor. The engineering indicates two 10K Resistors R1 & R2(R1 to PWR LED on front of board and R2 between Vcc & Rst on back of board.)

How have people been making your board? Do they just get the part without updating/informing your files? Anyway - I'd bought components for two boards. So, for now I'm using the second board's part to complete and need to order too more 10K resistors. Ack... Shipping....

Fabio - Thank you for your effort and distribution. A fun opportunity to learn and play.

We tried skillet reflow and it did not produce good results with our electric. It took too long to cook. We are using a silver based paste with a melt ~430F. So, we resulted to hand soldering and with silver wire. Not bad. Maybe on the second board I'll use my iron. ;-)

Nope! There is only one 10K

Submitted by fabio on Wed, 2011-08-24 23:52.

Nope! There is only one 10K resistor which is the pullup for the reset line which has to be on the back of the Femtoduino PCB. The resistors for the LEDs are 330 Ohm and are included in the BOM and Mouser cart.

For reflowing, I use a pizza oven (do not ever use it for food again once used for soldering, even if you clean it) or an hot air gun. Never had good results with the skillet.

10K x 2

Submitted by Brian (not verified) on Thu, 2011-08-25 02:43.

Sorry ---- Your Femtoduino-20101230_0221.pdf schematic in the KiCAD files shows the PWR LED as a 10K. And if you zoom into the PWR resistor R1 within the KiCAD board design it is labeled as a 10K. Oh well, getting good at reworking/reflow on near sub-micro flecks. Too much fun. :-)


Refer to the schematics

Submitted by fabio on Thu, 2011-08-25 09:11.

Refer to the schematics linked in this article. They should be correct.

Does anyone have a drawing showing parts placeent?

Submitted by ron k jeffries (not verified) on Tue, 2011-08-23 20:52.

I may be the first person to hand this off to a shop
to have them assemble. Other than tthe schematic and
a picture, it would be Most Useful to have a simple drawing showing part locations etc.

Can somebody who understand this better than I do know out something that while not
pretty, convey information.

For example, where should the red vs green LEDs go? and on and on. ;)

Thanks for your patience. (I hope you are patient...)

fyi I am using services of long time friend Juan Potau and his crew at Vareda Engineering.



Submitted by Brian (not verified) on Wed, 2011-08-24 22:51.

Ron, Time to ramp up and get the tools and learn the stuff. Since you are going into production you have to do some work. Eh?

My kids and I and all the rest of us are giving it a go. KiCAD is kinda cool.

of KiCad learning and the build is DONE (next: testing)

Submitted by ron k jeffries (not verified) on Wed, 2011-08-24 23:20.

I agree, I have a LOT to learn, and that includes KiCad.
I am stuck at such a low level: downloaded the Windows version,
have not figured out how to unpack it with PeaZip.

Maybe I'll try another tool.

I actually did get the breakout board file extracted,
but there are maybe a ten or so different files with different
file extensions, and (as best I can tell) no overarching
project that KiCad can read in. I am sure that if I sit down
(maybe via Skype or whatever) with someone who understands KiCad
I'll get rolling Real Soon Now.

having said that, my five Femtoduinos are already built. At the
last minute the production house realize they had a couple of
parts off the BOM that they had not used. They figured out the parts
belong on the back of the PCB. All doen,
easy peasy, lemon squeezy.

Part placement can be

Submitted by fabio on Wed, 2011-08-24 01:15.

Part placement can be understood by opening Femtoduino Kicad designs. That should be trivial for someone into PCB assembling.

Production note

Submitted by ron k jeffries (not verified) on Wed, 2011-08-24 01:20.


the issue is that an assembly house does not use KiCad.
They pushed ahead and assembled the Femtoduinos based on photos
and the schematic. I hope we got it right. ;)

I will download KiCad. I have never used it myself, shame on me.

If they used photos, check

Submitted by fabio on Wed, 2011-08-24 01:27.

If they used photos, check with them that they didn't forget the 3 components on the bottom of the board.

Femtoduino Production

Submitted by Alessandro Ancillotti (not verified) on Mon, 2011-08-22 10:27.

Hello, do you plan to do a "mass production"?
Maybe would be a good idea to feature your project on Kickstarters and have the kickstarters page featured on hackaday. I'm sure it will gain a lot of resonance and many people would be willing to found the project.

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