I'm probably getting ahead of myself diving into this before the sensor
API is nailed down, but if we wanted to add some generic helper
functions that make use of the sensor API, what would be a good location
or what to organize them as a package? It isn't always easy to organize
things like this by sensor type since there is a lot of overlap.
I can think of two helper packages we might want to add as a core test
case, that are useful for testing and getting actionable, useful output
from the sensor API:
ORIENTATION
Using only an accelerometer you can get rough roll/pitch values:
https://github.com/microbuilder/LPC11U_LPC13U_CodeBase/blob/development/src/drivers/sensors/accelerometers/accelerometers.c#L81
If you add a magnetometer you can get rough roll/pitch/heading values:
https://github.com/microbuilder/LPC11U_LPC13U_CodeBase/blob/development/src/drivers/sensors/sensorfusion.c#L78
If you add a gyroscope, you can do proper 9DOF sensor fusion using a
variety of algorithms and get better quality roll/pitch heading
(madgwick, mahoney, etc.).
All of this will require at a minimum magnetometer calibration to
compensate for hard and soft iron errors, and probably gyroscope
calibration to remove the zero drift error. Accel calibration helps, but
isn't as critical as the mag and gyro.
All of the above can probably be fit into a package based on sensor
'orientation', which might be a natural organizational unit?
FILTERS
A second very important helper unit is something that implements basic
DSP algorithms to filter raw sensor data. This is critical in my
opinion, but often neglected in open source systems.
This should contain things like a simple moving average filter, a basic
FIR and IIR filter (that can take coefficients from Octave/Matlab), and
a other very common but useful filters that will help remove noise from
less expensive sensors like the lsm303dlhc.
For example, see:
* *iir.c* here:
https://github.com/microbuilder/LPC11U_LPC13U_CodeBase/tree/development/src/drivers/filters/iir
* Simple and weighted moving average filters here:
https://github.com/microbuilder/LPC11U_LPC13U_CodeBase/tree/development/src/drivers/filters/ma
The iir.c example above has some notes on calculating the coefficients
for a 2 pole butterworth filter, or determining the coefficients
internally. It's a limited example, but I think the right direction to
move things:
* Octave Butterworth Example:
https://github.com/microbuilder/LPC11U_LPC13U_CodeBase/blob/development/src/drivers/filters/iir/iir.c#L57
* Calculating Butterworth Directly:
https://github.com/microbuilder/LPC11U_LPC13U_CodeBase/blob/development/src/drivers/filters/iir/iir.c#L269
BONUS POINTS: PEDOMETER
A third package that could be implemented that would be a useful example
for BLE is taking accelerometer data and turning it into a pedometer,
which can be done with some reasonably straight forward code. I have
some code I can recycle for this, but it isn't publicly available on
Github.
I think this is interesting for BLE and I can help here, but the two
above are more critical.
Kevin
PS: Some of the code above is quite old and I'm not terribly proud of it
and would do things differently today and I've reimplemented these
elsewhere differently, but I think the examples are at least valid as an
illustration or where things need to move to be useful in the real world.
