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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* On the table face up values are 0, 0, -1000  (face down would read 0, 0, 1000)
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* On the table on botton side (landscape): 0, -1000, 0
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* On the table on right side (portrait): -1000, 0, 0
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* In any other position any mix of those 3 values.
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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:
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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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Simple example
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{{{
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  def get_rotation():
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    try:
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        f = open("/sys/class/i2c-adapter/i2c-3/3-001d/coord", 'r' )
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        input=f.readline( )
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        f.close()
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        coords = input.split(' ')
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        x=0
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        y=0
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        z=0
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        try:
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            x=int(coords[0])
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            x=int(coords[1])
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            z=int(coords[2])
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        except:
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            return (0,0,0)
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        return (x,y,z)
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    except:
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        return (0,0,0)
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}}}
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The above is probably far from optimal, so please fix if you know how to read the data faster.
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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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