joerg at openmoko.org
Sat Aug 30 16:57:02 CEST 2008
Am Fr 29. August 2008 schrieb Andy Green:
> I don't know anything about advantage of having two,
The original idea of having 2 g-meters probably was to detect rotation. Alas
it turns out they aren't sensible and exact enough to do this trick for
anything other than quick rotation shaking motion out of your forearm, given
the maximum possible distance between them on a phone. At least for rotations
in the range <1/sec it seems doesn't help.
Nice theory, but in pratice we needed one g-meter plus a 3-axis-gyro (example:
to do this right.
> Analogue ones are not that great anyway as I said we have to run them
> all the time instead of using the threshold quench stuff. As Harald
> said noise from routing would definitely make trouble on analogue
> version of LIS302 (ALB), it has 32K output impedence already, so they
> would have to be buffered with opamp at the device before the long
> routing. But with that and considering unusually low bandwidth on them
> so a capacitor at the ADC input to filter them too is possible, it would
> be OK I think.
We need to integrate analog signal with a capacitor anyway, to get true
integral of acceleration during last sample-window. Not trivial.
So we don't probably like to use analog g-meter, as it will bring maybe a
dozen other components to the board, like opamps, C etc.
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