Accelerometers
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
| Position | X | Y | Z |
|---|---|---|---|
| Lying on table (back down) | 0 | 0 | -1000 |
| Lying on table (face down) | 0 | 0 | 1000 |
| Sitting on table (bottom edge down) | 0 | -1000 | 0 |
| Sitting on table (right edge down) | -1000 | 0 | 0 |
| Sitting on table (left edge down) | 1000 | 0 | 0 |
| Bottom right corner down (approx.) | -500 | -500 | 0 |
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 (note the inverted sign of y):
angle_in_radians = atan2(x, -y)
Similar, Y and Z can be used to calculate the pitch.
Python
Using the sysfs interface:
def get_rotation():
f = open("/sys/class/i2c-adapter/i2c-3/3-001d/coord", 'r' )
coords = [int(w) for w in f.readline().split()]
f.close()
return coords
References
- ↑ Tom Pycke, Accelerometer to pitch and roll