Maemo Wiki Mirror - User contributions [en]

Accelerometers

2010-01-18T13:04:56Z

189.115.169.82: /* sysfs */

Fremantle provides an accelerometer API. Currently<ref>[https://bugs.maemo.org/show_bug.cgi?id=4724 #4724] ''Lack of official documentation on how to use the accelerometer''</ref> there are two interfaces available:
# 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.)
| -500
| -500
| 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 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:

angle_in_radians = '''atan2'''(''y'', -''z'')

== Python ==

Using the sysfs interface:
<pre>
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
</pre>

== 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)

<pre>

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;
}
</pre>

== References ==


<references/>


[[Category:Development]][[Category:Fremantle]]

Accelerometers

2010-01-18T13:03:12Z

189.115.169.82: /* Using the data */

Fremantle provides an accelerometer API. Currently<ref>[https://bugs.maemo.org/show_bug.cgi?id=4724 #4724] ''Lack of official documentation on how to use the accelerometer''</ref> there are two interfaces available:
# 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.)
| -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<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''):

angle_in_radians = '''atan2'''(''x'', -''y'')

Similar, ''Y'' and ''Z'' can be used to calculate the pitch:

angle_in_radians = '''atan2'''(''y'', -''z'')

== Python ==

Using the sysfs interface:
<pre>
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
</pre>

== 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)

<pre>

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;
}
</pre>

== References ==


<references/>


[[Category:Development]][[Category:Fremantle]]

Accelerometers

2010-01-18T13:02:41Z

189.115.169.82: /* Using the data */

Fremantle provides an accelerometer API. Currently<ref>[https://bugs.maemo.org/show_bug.cgi?id=4724 #4724] ''Lack of official documentation on how to use the accelerometer''</ref> there are two interfaces available:
# 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.)
| -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<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''):

angle_in_radians = '''atan2'''(''x'', -''y'')

Similar, ''Y'' and ''Z'' can be used to calculate the pitch.

angle_in_radians = '''atan2'''(''y'', -''z'')

== Python ==

Using the sysfs interface:
<pre>
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
</pre>

== 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)

<pre>

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;
}
</pre>

== References ==


<references/>


[[Category:Development]][[Category:Fremantle]]