Editing Accelerometers

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#REDIRECT [[N900 accelerometer]]
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Fremantle offers the possibility to play with accelerometers. There is a plan to offer a proper interface for accelerometers in Maemo, but if you want to try out before there are a couple of ways to do it.
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See also the [http://talk.maemo.org/showthread.php?p=288990 related thread] in talk.maemo.org.
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== D-Bus ==
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Thomas Thurman ([http://twitter.com/marnanel marnanel]) has put together a simple demo of an application using accelerometers using the D-Bus interface. You can find sources and .deb up at http://people.collabora.co.uk/~tthurman/sandcastle/
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== sysfs ==
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Another way is to use the sysfs file information.
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/sys/class/i2c-adapter/i2c-3/3-001d/coord
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When reading that file you get 3 values X, Y and Z. Values are in mG (milli G). 1000 = 1 G
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{| class="wikitable"
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|-
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! Position
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! X
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! Y
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! Z
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|-
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| Lying on table (back down)
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| 0
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| 0
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| -1000
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|-
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| Lying on table (face down)
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| 0
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| 0
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| 1000
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|-
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| Sitting on table (bottom edge down)
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| 0
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| -1000
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| 0
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|-
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| Sitting on table (right edge down)
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| -1000
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| 0
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| 0
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|-
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| Sitting on table (left edge down)
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| 1000
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| 0
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| 0
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|-
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| Bottom right corner down (approx.)
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| -500
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| -500
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| 0
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|}
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These are theoretical values. In real life your mileage will vary.
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== Using the data ==
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The ''X'' and ''Y'' values can be used to calculate<ref>Tom Pycke, ''[http://tom.pycke.be/mav/69/accelerometer-to-attitude Accelerometer to pitch and roll]''</ref> the roll (that is, clockwise rotation) using the ''atan2'' function (note the inverted sign of ''y''):
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  angle_in_radians = '''atan2'''(''x'', -''y'')
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Similar, ''Y'' and ''Z'' can be used to calculate the pitch.
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== Python ==
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Using the sysfs interface:
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<pre>
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  def get_rotation():
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    f = open("/sys/class/i2c-adapter/i2c-3/3-001d/coord", 'r' )
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    coords = [int(w) for w in f.readline().split()]
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    f.close()
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    return coords
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</pre>
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== References ==
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<small>
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<references/>
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</small>
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[[Category:Development]][[Category:Fremantle]]

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