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.

I was thinking. It would be

Submitted by apburner (not verified) on Sat, 2011-06-18 04:37.

I was thinking. It would be nice to have the fempduino and freeimu combined on one board. Just run the I2C lines on the board and bring the other pins to the outside. Just a thought. Also maybe a mega2560 instead
The 2560 would make a great quadcopter controller.

I can't wait till I can buy some

Submitted by Tim (not verified) on Thu, 2011-06-02 14:03.

Making one of these is beyond me (I am really into software more than building hardware). I can stick big things together but SMD, just don't have the time to get that right ;-)

So I am really hoping I can buy about 10 of these in about 3-4 months time.

I am starting off with Jeenodes at the moment, and am searching for something even smaller (combined with a RFM12B transceiver) to build a set of wireless, solar charged, battery powered sensors stuffed into solar garden lights.

Theres not a lot of room in the solar light, so a femtoduino could be ideal.

I will watch this space avidly and see how things develop.

Re: I can't wait

Submitted by Tom B (not verified) on Thu, 2011-06-02 19:09.

I've got about 100 RFM12B modules, I'm looking at using the module on the 3.3V Femtoduino shield :). I've also got the LIPO dropout/charge module from SF and solar panels. Doing some testing now. JCW (JeeLabs) does great stuff, but IMHO I like how the Femto brings out all the pins.

Tom

Hi Let me know how your solar

Submitted by Tim (not verified) on Fri, 2011-06-03 04:00.

Hi

Let me know how your solar testing goes. I was planning to use 2000mah NiMH's as they already fit inside the solar lights etc... which gives me a discrete ready made charger/package (with some added bits of course).

The work jcw is doing at jeelabs is pretty awesome and extremely instructive. For 90%+ of my applications Jeenodes pin outs are fine. I only one node that needs a full arduino. The awesomeness of Femtoduino for me is the size! One of them back to back with the rfm12b is one really small wireless package.

I will sort out my software on Jeenodes, and then hopefully I can source some ready made femtoduino's rather than going with a mini.

Cheers

T

Uses

Submitted by Steve (not verified) on Wed, 2011-06-01 15:48.

I have been looking at the posts for this neat little board and I see a bunch of folks fussing because is doesn't have a .1 pin spacing. But what I see in this fantastic little board is the ability to put arduino ease of use into a tiny little space. I am thinking maybe N or Z scale train building with one of these in them to control lights or tiny servos to open and close doors. Or maybe a hexapod robot with one of these on each leg to control it and report back to a central master that is sending commands out Via I2C bus. This is just a couple of the many things that can be used. It is not only small but lite weight too.
Steve

What discussions are you

Submitted by fabio on Wed, 2011-06-01 16:20.

What discussions are you referring to exactly? I'm always curious to read what people think about my work..

Thanks for the appreciation!

http://groups.google.com/grou

Submitted by Steve (not verified) on Thu, 2011-06-02 16:07.

http://groups.google.com/group/dorkbotpdx-blabber/browse_thread/thread/c...

This thread in particular says it all. But I have found others. The only thing I would love to see if you decide to do another version is 2 mounting holes for 2-56 bolts. This way you could mount it solid to something and just run wires to it and not headers.
Just a thought. I may look the board over and see if there is space for 2 small holes without cutting traces. Even 0-80 bolts would be OK if they make standoffs that small.

bolts can be overkill

Submitted by zencuke (not verified) on Fri, 2011-06-03 00:48.

Suggestion: With a board this small and light two bolts would usually be overkill. It is hard to see why even one bolt is necessary. Some double sided tape is probably fine, or support it with the soldered wires. If there will be a lot of vibration a dab of hot melt glue to hold a wire or wires in place might do it. I like rubber banding small boards in place. Trying it down with a little thread would work for most applications with hot melt at a strategic point to tack the thread in place. Hot melt glue can be superior to rigid connections like bolts because it transmits less energy from vibrations and can result in less stress damage. It is popular in low cost commercial products.

Bolts make more sense for attaching boards with higher mass.

Well, I've been talking in

Submitted by fabio on Thu, 2011-06-02 16:32.

Well, I've been talking in that thread! ;-) Nothing to worry about those critics..

You simply can't go this smaller without using .05" connectors in a 2 sided board. And really there is no need to make Femtoduino smaller than what already is.. it would be simply too painful to use.

Adding mounting holes is not possible.. traces are almost everywhere in the pcb. Including them into a redesign would make femtoduino bigger so I won't do it.. but of course you can do that starting from my designs.

Another possibility may be to use exactly the current design and add mounting holes in a side part using scoring.. just as in this breakout board.

Ya double sided tape and hot

Submitted by Steve (not verified) on Fri, 2011-06-03 15:38.

Ya double sided tape and hot glue do seem the better choice for something this small. Thanks I will do that.
Steve

have ordered some boards

Submitted by apburner (not verified) on Sun, 2011-05-29 01:39.

Well my order is in for 9 Boards
Have been told they will be there
Wed. Now for the soldering of smt.

Good luck mate! Please post

Submitted by fabio on Wed, 2011-06-01 16:19.

Good luck mate! Please post here if I can be of any help!

Femto #1 running from Arduino V22 IDE

Submitted by Tom B (not verified) on Fri, 2011-05-27 20:33.

It's alive! I can download sketches from version 22 of the Arduino IDE from my Linux box. Blinky lights and serial work fine along with the reset. Time for more testing, pictures and some video :)

Fabio great stuff! Thanks.

Pictures! Videos!

Submitted by fabio on Sun, 2011-05-29 08:42.

Pictures! Videos!

Supplies in the UK?

Submitted by Rory Watson (not verified) on Thu, 2011-05-26 13:16.

Seeing as I have very little experience with surface mount components, and specifically no access to equipment for soldering such parts, I was wondering if anyone knows the best place in the UK, or close to if shipping isn't too high, that I could have very small quantities of these boards fabricated. Or if anyone within the UK is capable of fabricating some, surplus to their own requirements, that I could purchase in low quantities, i.e. less than 10. And if anyone would have a rough estimate for how much would be charged, it would be greatly appreciated.

Re: Supplies in the UK?

Submitted by Tom B (not verified) on Fri, 2011-05-27 15:20.

Hi Rory,

I'm one possibility, depending on shipping costs. I'm across the pond in the US, and I don't know if shipping will be prohibitive. I'm looking into selling assembled, tested, bootloader installed Femtoduinos for around $16.17US with local tax or around $15 without tax. I need to look into the tax matter a little more.

My first Femtoduino is soldered together and looks great (IMHO). Power subsystem works and I should be brining up the ATmega328 today.

I think everything is ROHS EXCEPT the solder paste which is standard 63/37 lead/tin.

Don't know if that matters. Longer-term, I'll move to a non-leaded solder, but right now I'm using leaded as it works better, is more reliable, reflows better at lower temperatures and is less toxic during reflow.

Tom B.

Hi, I'd be interested in

Submitted by Dan (not verified) on Mon, 2011-08-08 22:06.

Hi, I'd be interested in buying if your still up for it? In UK as well, let me know..

interested in buying assembled tested Femtoduino in US

Submitted by Ron K Jeffries (not verified) on Sat, 2011-05-28 21:43.

I am interested to buy one, play with it, then may want to buy more.

I think everything is ROHS

Submitted by fabio on Fri, 2011-05-27 20:51.

I think everything is ROHS EXCEPT the solder paste which is standard 63/37 lead/tin.

Well, that's not good.. leaded solder paste makes the whole board not ROHS compliant and can't be sold in the EU.

Hi Tom, I will definitely

Submitted by Rory Watson (not verified) on Fri, 2011-05-27 19:09.

Hi Tom, I will definitely keep you in mind, but from a quick look at postage cost it may indeed be prohibitive. From what I have looked at so far, based on a rough estimate of weight and package volume, it would cost about £40 (roughly $65 I think) to have very few shipped over :( . And I just don't have funding to offset that cost with a higher quantity, even if I could sell them on in the UK with no/little profit. It is a shame because the unit cost you have set is about what I was hoping to pay.
Rory W

I'll have to check rates here, the first est. was only $25US

Submitted by Tom B (not verified) on Fri, 2011-05-27 20:28.

Also, I'll check with Laen. It's may be quite possible to bundle PCBs and built boards. Next time Fabio gets boards, the "Femtos" could "ride for free". I'd be surprised is Laen didn't ship anywhere in the UK.

Quite a wonderful time.

The shipping costs looks too

Submitted by fabio on Fri, 2011-05-27 19:44.

The shipping costs looks too pessimistic in my opinion. You can put about 50 Femtoduinos into a standard letter size envelope.. I don't understand why you are thinking about such big costs.

Hi Fabio, If they can be fit

Submitted by Rory Watson (not verified) on Sat, 2011-05-28 01:16.

Hi Fabio, If they can be fit into an envelope, it should bring the cost down, I was accounting for a 5cm^3 package, though would an envelope be sufficient to keep them protected during transit? I'm definitely interested in removing the duemilanove from under the dash of my car :P and I have 3 or 4 more projects in mind.

Rory W

Re: Shipping costs NOT prohibitive

Submitted by Tom B (not verified) on Sat, 2011-05-28 20:49.

Laen's estimate is < 3 or 4 US dollars. He ships to the UK and I'm guessing Italy often. Fabio uses his PCBs as do many of us.

I think the only issue now is solder paste. Rory let me know your time frame.

Tom

Deadlines, voltages and such

Submitted by Rory Watson (not verified) on Sun, 2011-05-29 15:33.

Hi Tom, I don't really have any deadlines for when I would require them for, right now I can afford about 3 femtos based on the quote from before and the shipping estimate from Laen, I may be able to afford 5 by the end of the week, dependent on when I get payed by work. Also I have one query, are you fabricating 5v or 3.3v femtos, not that it matters so much, but thought I should ask.

Rory W

ROHS solder paste:

Submitted by fabio on Sat, 2011-05-28 21:50.

Re: A few Q's on building the Femtoduinos

Submitted by Tom B (not verified) on Wed, 2011-05-25 02:33.

I've got a couple simple questions:

1) What should I do with the SW 1 pads ? Leave them open ? I don't have a SMT switch and it wasn't in the Mouser BOM.
2) Does the silk screen on the front have the 10 uF polarity reversed in Kicad ? The Line should go with the Anode (+) correct ? That's the way the chips are soldered on your JPG of the Femtoduino.
3) Minor, Two RED LEDs are in the Mouser BOM instead of 1 RED and 1 GREEN FYI.

Thanks !

Tom B.

Tom, I've updated the Mouser

Submitted by Ricardo Arturo Cabral (not verified) on Thu, 2011-05-26 14:06.

Tom, I've updated the Mouser BOM / Project so that it comes with a green and a red LED.

Thanks!

Submitted by fabio on Thu, 2011-05-26 14:45.

Thanks!

1) that pads are not for

Submitted by fabio on Thu, 2011-05-26 09:09.

1) that pads are not for soldering a switch.. the idea is to use a small rigid wire and touch the two sides to short them out when needed to reset the board.

2) yes, check the pictures and the video for the correct orientation. Be careful as tantalum caps really don't like reverse voltages (may even explode :-( ).

3) I didn't noticed that. If you could provide a link to a revised Mouser BOM I'd appreciate it.

Thanks!

tantalum in reverse. Mine got

Submitted by Brian (not verified) on Wed, 2011-09-14 21:36.

tantalum in reverse. Mine got super hot then died.... :-( But, I've since soldered in new ones and the power circuit lights the LED. Now to test program and test. --- FUN ! ----

Are the Kicad and Gerber silk screen reversed for the tantalum placement?

Yes, the silkscreen is wrong.

Submitted by fabio on Thu, 2011-09-15 07:41.

Yes, the silkscreen is wrong. Please refer to the pictures I published for the correct placement.

Tom, you can leave the SW

Submitted by Ricardo Arturo Cabral Mejía (not verified) on Thu, 2011-05-26 00:30.

Tom, you can leave the SW pads as they are. I looked around and could not find a switch that was SMD and that small.
The silk screen has the polarity inversed in KiCad, I learnt that the hard way. The correct way to place the capacitors appear on the picture.
The Mouser BOM was created by me for others to use as they please.
You may add the project to your cart and then proceed to change the parts you don't like.

Thanks for your contribution

Submitted by fabio on Thu, 2011-05-26 09:10.

Thanks for your contribution to the discussion Ricardo.

Re: Building Femtoduinos -- Today's stencil

Submitted by Tom Billman (not verified) on Tue, 2011-05-24 00:26.

The link at http://tinyurl.com/3c7onvz show the stencils I'll be using to create some Femto's..

They are cut from 2 mil Kapton on an Epilog.

Tom B.

Awesome! Where did you get

Submitted by fabio on Tue, 2011-05-24 00:52.

Awesome! Where did you get those stencils made?

Looking forward seeing your Femtos built! Keep us posted! ;-)

DIY, Cut the Kapton on the

Submitted by Tom B (not verified) on Wed, 2011-05-25 02:25.

DIY, Cut the Kapton on the Epilog at the local TechShop. My buddy has a Full Spectrum Laser, but we haven't fully dialed it in. I'll likely be building my own Laser, but that's after the Pick-n-Place and wrapping up my Reflow oven.

Backed the back-side of the Femtoduino today. Placed my first 0402s YAY...

Fabio, let me know if you'd like some free stencils. Assuming import duty isn't TOO expensive I can send them to you.

couple of questions regarding the design of the board

Submitted by xa4 (not verified) on Sun, 2011-05-08 15:26.

Kudos for releasing this nice femtoduino board!

When reading the datasheet of the mic5205 voltage regulator (http://www.micrel.com/_PDF/mic5205.pdf), the typical application uses only a 470pF and a 2.2uF (minimum) capacitors..

Could you please explain what is the rationale for putting the two 10uF polarized and the 0.1uF decoupling capacitors (like on the arduino pro mini)?

Are the values of the capacitors the same for the 3.3V and the 5V version ?

Also, you wrote about eventual enhancements for the V3.. could you please write about them ?

Thank's in advance for your answers,
Xavier

Hi Xavier, Could you please

Submitted by fabio on Sun, 2011-05-08 15:45.

Hi Xavier,

Could you please explain what is the rationale for putting the two 10uF polarized and the 0.1uF decoupling capacitors (like on the arduino pro mini)?

There is not a strong rationale behind this.. I simply copied what Sparkfun guys were doing with the pro mini. I also noticed that the datasheet suggest a simpler cap schematics but I didn't risk and simply used the Sparkfun guys approach.

Are the values of the capacitors the same for the 3.3V and the 5V version ?

Yes

Also, you wrote about eventual enhancements for the V3.. could you please write about them ?

The most important thing to change would be increasing the space between the top and right connectors.. right now it's perfectly fine but if the user need to use female or male 0.05" connectors on them they have to use a file to smooth the connectors edges as otherwise the wouldn't plug next to each other.

The possible other minor enhancement for a possible v0.3 would be:

  • moving all the components to the top side. Right now there are 2 caps and one resistor on the bottom side but this makes hand assembling harder.
  • slightly increase the size of the silkscreen for the pins
  • find a voltage regulator which wouldn't make use of tantalum caps

If you wanna jump in and contribute a Femtoduino v0.3 with the above changes I would surely appreciate that!

I had the same exact problems

Submitted by Ricardo Arturo Cabral Mejía (not verified) on Mon, 2011-05-09 20:19.

I had the same exact problems with the pin spacing.. I had to trim the connectors so they would fit together.

College Lab Use

Submitted by Anonymous (not verified) on Sun, 2011-04-10 16:55.

We are working with very small, lightweight, aero type vehicles in an undergraduate lab, and this controller fits the bill. If you think someone would be making these in the next couple of months or so, I'd be very interested in at least 50. Otherwise, it's going to be some late nights and bleeding eyes! Wonderful project. The arduino is great, and open source is a fantastic idea. Americans don't get it, it's called sharing, and I love it. I'll try to give back anyway I can. Thanks again.

I can ask for production cost

Submitted by mclien (not verified) on Sat, 2011-04-16 14:01.

My wife works in a company (germany), which produces these tings.
I can ask her for a offer about this. I think of 1/9 braaaekout boards and femtoduino.
I think the price offer would be for free...

I've ordered some from Laen

Submitted by Will (not verified) on Sat, 2011-03-19 00:12.

Hi there. I've ordered three Femtoduino boards and three breakouts from the boardhouse you recommended. I'm looking forward to receiving them, although the soldering will be a challenge...

The Femtoduino will be great for a data-logging and sensing project I'm working on - I'll let you know how the testing goes.

Cool! James from Dorkbot PDX

Submitted by fabio on Sat, 2011-03-19 01:49.

Cool! James from Dorkbot PDX told me about many Femtoduino orders lately ;-)

Let me know if you need assistance in the soldering.. I'd love to see a picture of your Femtoduino once completed.. keep me posted!

p.s.: what kind of sensor data logging are you into? I'm also working on something like that soon.

Femtoduino for sensing

Submitted by Will (not verified) on Thu, 2011-05-19 09:47.

I work at UCL Energy Institute, and we're really interested in logging the output of sensors to do with temperature, humidity, light, as well as events such as doors opening, room occupancy etc.

I received the Femtoduino boards a while ago, but have been on a long holiday. The components have arrived now as well (they took a while from Mouser because the crystals were out of stock).

Over the next few weeks I'm going to think about how to best go about soldering these all together.

I'll keep in touch with the progress.

Regards,

Will

Great! Keep us posted and

Submitted by fabio on Thu, 2011-05-19 11:22.

Great! Keep us posted and comment here if you need assistance in soldering/building/programming them!

Extra Pin

Submitted by Brett (FightCube) (not verified) on Fri, 2011-02-25 05:19.

Was just looking at your schematic and noticed you have pin 33 listed as GND, on a 32 pin part ;-)

Nice work btw on the whole project.

That's intentional. Pin 33 is

Submitted by fabio on Fri, 2011-02-25 09:14.

That's intentional. Pin 33 is the big pad placed behind the ATMEGA, which has to be connected to ground. So, we do actually have 33 pins.

My Bad

Submitted by FightCube (not verified) on Sat, 2011-02-26 07:30.

I was working on a design using the TQFP package and looking at your schematic. I forgot about a heat sink pad!

Ok, well maybe I should have

Submitted by fabio on Sat, 2011-02-26 09:37.

Ok, well maybe I should have marked it as pin 0 so that it would have been clearer that it is something special.. maybe next time.

Thanks for your contribution and for your interest in Femtoduino!