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Finger tap vibrations via Accelerometer

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-Fire-

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Hi,

I am not sure if this is the right section to post in but this seemed to be most fitting. Apologies elsewise.

I have taken up a standard accelerometer logger application in my android smartphone and recorded the data.

I placed it on a wooden table and noted down the reading per 100 ms. I took the readings for about 5 seconds.

I then placed it on the same position and slightly tapped my fingers over the table. I noted down the readings.

The accelerometer readings were along x, y and z axis.

I then tried to see the difference between the values of the first and second- basically to see if my accelerometer is picking up the vibrations from my finger tapping.

I noticed slight changes in Z values at various intervals. None in X and Y. The change was greater as well as lesser than the values observed previously.

The value without any tapping was flickering between 9.5 and 9.6 whereas the in the tapping I noticed some values in 9.4, 9.2 and 9.8-9.9


Is this seemingly correct?

If not, can anyone give me some idea of how to go about it? Are the value changes supposed to be these slight only? Someone please shed light on this in a "dummy" (me) friendly way please?


P.S: I want to use the readily available accelerometer in the phone only. And this is actually possible with the standard mobile accelerometer, I have seen researches with published work use these only.
 

Do you know what the sample rate of the accelerometer channels are ?
A finger tap has a duration of less than 50 milli-second .
If the accelerometer sample rate is more than 50 milli second, events can be missed
 

I changed the logging values to 10 ms i.e. it logs at every 10 ms. That should capture the event, right? I observe the same pattern as described above.

My question is whether the change observed should be so minute only and that too along one axis only? I mean, am I getting the correct data or not? If not, then how to get correct data? and how do I verify it?

And can you please explain to me in a noob-friendly way how this whole vibrations thing works?
 

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