|
|
| (4 intermediate revisions by the same user not shown) |
| Line 1: |
Line 1: |
| [[Open development/Maemo roadmap/Fremantle|Fremantle]] provides an accelerometer API. There are currently [https://bugs.maemo.org/show_bug.cgi?id=4724 two interfaces available]:
| | #REDIRECT [[N900 accelerometer]] |
| # D-Bus | |
| # sysfs
| |
| | |
| See also the [http://talk.maemo.org/showthread.php?p=288990 related thread] at talk.maemo.org.
| |
| | |
| == D-Bus ==
| |
| | |
| 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/
| |
| | |
| == 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 (provided on one line, separated by white space). Values are in mG (milli G). 1000 = 1 G
| |
| | |
| {| class="wikitable"
| |
| |-
| |
| ! 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.)
| |
| | -707
| |
| | -707
| |
| | 0
| |
| |}
| |
| | |
| These are theoretical values. In real life your mileage will vary.
| |
| | |
| An example can be found at: [http://git.zimmerle.org/?p=inclinometer.git;a=summary]
| |
| | |
| == Using the data ==
| |
| | |
| 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 pitch (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 roll:
| |
| | |
| angle_in_radians = '''atan2'''(''y'', -''z'')
| |
| | |
| == Python ==
| |
| | |
| Using the sysfs interface:
| |
| <source lang="python">
| |
| 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
| |
| </source>
| |
| | |
| And using the D-Bus interface:
| |
| <source lang="python">
| |
| import dbus
| |
| bus = dbus.SystemBus()
| |
| accel = bus.get_object('com.nokia.mce',
| |
| '/com/nokia/mce/request',
| |
| 'com.nokia.mce.request')
| |
| orientation , stand , face , x , y , z = accel.get_device_orientation()
| |
| </source>
| |
| x,y,z are the raw accelerometer measurements values, and the first three variables give text information about the device orientation. In particular, the first one informs about the landscape/portrait state.
| |
| | |
| == Smoothed C interface ==
| |
| | |
| This is a C function which returns smooth values from the accelerometer.
| |
| Designed for applications running at >=25fps (otherwise it lags)
| |
| | |
| (GPL code extracted from libliqbase: liqaccel.c)
| |
| | |
| <source lang="c">
| |
| static int ocnt=0;
| |
| static int oax=0;
| |
| static int oay=0;
| |
| static int oaz=0;
| |
|
| |
| static const char *accel_filename = "/sys/class/i2c-adapter/i2c-3/3-001d/coord";
| |
| | |
| int liqaccel_read(int *ax,int *ay,int *az)
| |
| {
| |
| FILE *fd;
| |
| int rs;
| |
| fd = fopen(accel_filename, "r");
| |
| if(fd==NULL){ liqapp_log("liqaccel, cannot open for reading"); return -1;}
| |
| rs=fscanf((FILE*) fd,"%i %i %i",ax,ay,az);
| |
| fclose(fd);
| |
| if(rs != 3){ liqapp_log("liqaccel, cannot read information"); return -2;}
| |
| int bx=*ax;
| |
| int by=*ay;
| |
| int bz=*az;
| |
| if(ocnt>0)
| |
| {
| |
| *ax=oax+(bx-oax)*0.1;
| |
| *ay=oay+(by-oay)*0.1;
| |
| *az=oaz+(bz-oaz)*0.1;
| |
| }
| |
| oax=*ax;
| |
| oay=*ay;
| |
| oaz=*az;
| |
| ocnt++;
| |
| return 0;
| |
| }
| |
| </source>
| |
| | |
| [[Category:Development]]
| |
| [[Category:Fremantle]]
| |
| [[Category:Hardware]]
| |
| [[Category:Sensors]]
| |
