Accelerometers
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Simple example | Simple example | ||
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def get_rotation(): | def get_rotation(): | ||
try: | try: | ||
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The above is probably far from optimal, so please fix if you know how to read the data faster. | The above is probably far from optimal, so please fix if you know how to read the data faster. | ||
| - | x, y and z values are in 1 G conditions between -900 and 900. Nominal state for each vector is 0. The values can be multiplied by the amount of Gs you may experience. | + | x, y and z values are in 1 G conditions between -900 and 900. Nominal state for each vector is 0. The values can be multiplied by the amount of Gs you may experience. |
== References == | == References == | ||
Revision as of 19:18, 28 July 2009
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.
See also the related thread in talk.maemo.org.
Contents |
D-Bus
Thomas Thurman (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/
sysfs
Another way is to use the sysfs file information.
/sys/class/i2c-adapter/i2c-3/3-001d/coord
When reading that file you get 3 values X, Y and Z. Values are in mG (milli G). 1000 = 1 G
- On the table face up values are 0, 0, -1000 (face down would read 0, 0, 1000)
- On the table on botton side (landscape): 0, -1000, 0
- On the table on right side (portrait): -1000, 0, 0
- In any other position any mix of those 3 values.
These are theoretical values. In real life your mileage will vary.
Using the data
The X and Y values can be used to calculate[1] the roll (that is, clockwise rotation) using the atan2 function:
angle_in_radians = atan2(x, y)
Similar, Y and Z can be used to calculate the pitch.
Python
Simple example {{{
def get_rotation():
try:
f = open("/sys/class/i2c-adapter/i2c-3/3-001d/coord", 'r' )
input=f.readline( )
f.close()
coords = input.split(' ')
x=0
y=0
z=0
try:
x=int(coords[0])
x=int(coords[1])
z=int(coords[2])
except:
return (0,0,0)
return (x,y,z)
except:
return (0,0,0)
}}}
The above is probably far from optimal, so please fix if you know how to read the data faster.
x, y and z values are in 1 G conditions between -900 and 900. Nominal state for each vector is 0. The values can be multiplied by the amount of Gs you may experience.
References
- ↑ Tom Pycke, Accelerometer to pitch and roll