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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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RGB Tumbler

5. November 2011 19:40 by Jens Willy Johannsen
Categories: Projects

For a new project I thought I'd like to do some RGB LED stuff. And I got the idea of making a small circuit (small enough to be put inside a ping-pong ball) that controlled one (or more) RGB LEDs from its physical orientation. Simply put, acceleration on the X, Y and Z axes would translate to intensity of the red, green and blue LED. And since there is always an acceleration of 1G towards the center of the Earth (also known as "gravity"), the color of the RGB LED would depend on its orientation.

So the system will comprise the following "blocks":

  1. Power
  2. MCU
  3. 3 axis accelerometer
  4. LED driver. Or maybe the LEDs can be controlled directly from the MCU.
  5. RGB LED. One or two.

When looking for parts there's a few things to keep in mind:

  1. Size matters. It must be as small as possible. I only recently started working with SMD components but already I can't imagine having to deal with those clunky, Soviet tractor-like through-hole components. But I still haven't gone all the way into reflow soldering. So I'm looking for primarily SOIC, TSSOP and TQFP packages. QFN packages are actually possible to hand-solder but it's not fun at all and LGA and BGA are pretty much impossible. For many-pin devices, SOIC is actually kinda big with their huge 1.27 mm pitch and 0.5 mm pitch TSSOP would be preferable.
  2. Power. As little as possible. I plan on running everything off a single 3V coin cell so voltage should be 2.7 to 3 volts and amps should be as few as at all possible.
  3. Availability. I much prefer to be able to get everything from one, local provider.

So off to the intertubes for some Googling…

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