FreeIMU: designing a free (as in speech) 9 DOM/DOF MARG IMU

UPDATE 2011-02-10: Check out FreeIMU project page for all the informations about FreeIMU!

In the past months I worked a lot on accelerometers, gyroscopes and digital compasses. I’m now pretty intimate with the ADXL345, the ITG3200 and the HMC5843.

I’ve been able to design and construct homebrew DIY breakout board PCBs for all of them (ADXL345 and ITG3200) and to create a nice library to use them which also implement a great sensor fusion algorithm capable of running on the Arduino without problems.

I’m now making the next step. Let me introduce FreeIMU.

FreeIMU is a 9 DOM/DOF MARG IMU based on the ADXL345, the ITG3200 and the HMC5843. As this is part of my Master of Science Project and that I completely share the openness of projects like Arduino, FreeIMU will be completely open: all the designs will be released under a Creative Commons Attribution-ShareAlike 3.0 Unported while all the software will be release under GNU GPL v3.

As my background is in computer science, I’m quite self-taught in PCB designs and in electronics in general. So, I’m now seeking review for FreeIMU’s schematics and PCB designs. If you have experience working with IMUs, designing PCBs or circuits and you would like to contribute to a free project please have a look at the designs and feel free to comment it.

I’m using kicad as schematics and PCB editing software. It’s free (as in speech) software and, once you get around its glitches, it works really well. Using non-libre software like EAGLE to design a free hardware like FreeIMU would have been simply senseless.
Note: I’m using a nightly updated version of Kicad, so if you have problems opening the files you might need to update your version of Kicad.

So, you’ll find the current Kicad based sources of FreeIMU in the attachments to this page just below. You’ll also need a library of components which I also attach here. For your convenience I attach also a pdf version of the schematics.

I plan to submit FreeIMU to DorkbotPDX PCB Order of the 13th December to have it constructed. I currently don’t see this as a commercial project but if someone is interested in FreeIMU I could sell a couple of boards.

Ok, so.. looking forward to hear your comments. Thanks!

UPDATE 2010-12-13:

FreeIMU designs have been sent for fabrications. Looking forward to receive the PCBs soon! I have received some interesting advices on the board design so the design sent to production has been slightly modified: there’s now space for an optional 10uF tantalum capacitor in package A and there’s more clearance for the mounting holes. The original design would have been making almost impossible screw FreeIMU as there were some capacitor just near the mounting holes.

You find the final PCB design in the attachments below. I also attach below the Gerber and drill files sent for production.

I’d like to thanks everyone who helped in reviewing and advising on FreeIMU. I’d like to thank especially Greg Peek from dorkbotpdf-bladder mailing list who convinced me on adding the 10uF cap and adding more clearance on the mounting holes. I’d like also to thank James Neal for suggesting the addition of the mounting holes in the first place and for taking care of organizing the PCB group order.

UPDATE 2010-12-22:

The FreeIMU project is progressing nicely.

Yesterday Laen received FreeIMU’s PCBs and they shuold have been
shipped to me today.

I’ve also been able to find cheap stencils from
http://www.smtstencil.co.uk/ .. They should have shipped the stencils
yesterday.

Meanwhile I ordered all the components to produce 10 copies of FreeIMU.

The code is now quite stable and I’m using it on my tangible user
interface prototype (basically it’s a sphere capable of detecting
taps, double taps and its orientation – more on this on my blog soon).

I should be able to produce the first boards around the first week of
January.. I’m really looking forward to it!

UPDATE 2011-01-02:

The interest this project is getting is huge! Thanks to everybody who contacted me about FreeIMU and to the people who already reserved FreeIMU units.

For those who are interested in buying one or more FreeIMU units here are the prices:

  • Fully assembled FreeIMU v0.1: 80 euro 70 euro with international shipping and pre-soldered female or male headers (at your choice) included. For multiple orders I can offer a discount, just get in touch with me.
  • FreeIMU v0.1 raw PCB: 15 euro with international shipping included and non-soldered female or male headers. Note: You will have to buy the ICs sensors by yourself and be able to reflow solder them.

If you want to buy one or more units please get in touch with me and I’ll reserve your units for you. The number of available units is limited and a strict first came first served policy will be followed so reserve your units as soon as you can to be sure to get one.

UPDATE 2011-01-14:

Still no signs of FreeIMU’s PCBs. It looks like Lean will need a better shipping option for us in Europe. More than 3 weeks already passed from the shipping of the PCBs from the USA to Italy and still no signs of them. Of course, we had the holidays in the middle, but that’s way too much!

UPDATE 2011-01-18:

Just created a FreeIMU project page on Launchpad. Using launchpad for FreeIMU development will give us some great advantages like: an high quality repository with bazaar, code and designs browsing, questions and answers, bug and features suggestions.. Moving the project to a public place was a step to be made.

So, from now on, you can download FreeIMU designs from it’s repository using:

bzr co lp:freeimu

UPDATE 2011-01-20:

Still no signs of FreeIMU v0.1 .. fuc**in Italian customs. Anyway, FreeIMU version 0.2 has been sent for fabrication and today it has been shipped to me. This time of course using FedEX which shouldn’t be so slow as regular mail. Let’s hope so..

Following some picture of FreeIMU v0.2:

UPDATE 2011-01-26:

FreeIMU is alive! First units of FreeIMU have been produced and I’m currently testing everything. Stay tuned!

AttachmentSize
FreeIMU kicad library2.48 KB
FreeIMU kicad sources (original and outdated version – not sent to production, only for reference)34.41 KB
FreeIMU schematics39.42 KB
FreeIMU kicad sources (final version sent to production)203.22 KB
FreeIMU Gerbers and drill files18.66 KB
FreeIMU_v0.1_gerbers.tar_.gz18.66 KB
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