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Archive for December, 2011

Creating custom enclosures

29. December 2011 21:04 by Jens Willy Johannsen
Categories: PCB

For another project (that I have shamefully neglected to write about) I decided I needed to put it into some kind of enclosure. And I since I couldn't find any off-the-shelf enclosures that fit I decided to make my own.
A little bit of googling let me to Shapeways that lets you create 3D printed models from your own 3D files in several different materials.

The models themselves can be created in pretty much any 3D modeling application (including the free SketchUp or Blender). I used Luxology's modo.
Obviously, exact dimensions are important. So I got PCB dimensions and coordinates from Eagle and used a caliper to measure the size of the battery and plugs and so on. And I created dummy objects for the battery and the PCB to make sure that everything fit. This is what I came up with:

Enclosure (click for larger version)

The stand-offs have 4.1 mm holes for threaded inserts to use with M3 machine screws (like these ones from RS).

And here with the dummy objects visible:

With dummy objects (click for larger version)

I exported the object to Wavefront OBJ format and uploaded it to Shapeways (I needed to rotate 90 degrees about the X-axis first in order for the preview image to render correctly on Shapeways) and specified the units as meters (since that's what modo uses by default).

The price came to €20.14 plus shipping (€8.38 for UPS shipping) for "white, strong, flexible" material. So now it's just wait and see how it turns out.

Bear in mind, that this is my first attempt at making a 3D printed object. I haven't even smoothed the edges or added support ribs or anything. Not to mention that I have only made the bottom part of the enclosure (it does however have a "lip" for mating with the top half).

For a much nicer custom enclosure, take a look at this one (also on Shapeways).

 

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Filtering ADXL335 data

7. December 2011 12:07 by Jens Willy Johannsen
Categories: Projects

As mentioned in my previous post, noise from the ADXL335 accelerometer readings result in flickering light. And I don't want that.

So in order to smooth the sensor data I will implement a filter. Either a simple moving-average filter or a nearly as simple low-pass filter.

(Read the entire post to see chart comparisons of the two filtering methods.)

Read the entire post »

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RGB Tumbler done

7. December 2011 9:36 by Jens Willy Johannsen
Categories: Projects

I got the PCBs yesterday and promptly set about assembling one. The really interesting part of that, of course, was whether it was possible to hand-solder the LFCSP ADXL335 accelerometer ("lead frame chip scale package" – who comes up with these names?).
It turned out it was, in fact, possible. The bottom pad is not soldered, of course, and even though I had made the pads longer to be able to reach them with the soldering iron it was still kinda tricky. But it worked. In first attempt, even.

And the little tumbler thingie works perfectly! (I'll post a video.)

But I need to tweak the firmware a bit. The sensor data from the accelerometer has quite a bit of noise and this results in too flickering light. So I will need to implement a filter of some sort. Either a moving-average filter or a simple low-pass filter. And maybe also some way of "snapping" to 0, 0.5 and 1 values in order to get more "clean" colors. Stay tuned…

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