That's where getting an accurate sample as fast as you can comes into play.
But, with the A/D on a PIC, you can sample too fast and kill your accuracy.
So, you've got to play with it and find a balance between sampling fast and keeping a decent amount of accuracy. Also, whether or not the acceleration is constant isn't really an issue. The speed of sampling takes care of that for you. The less time between the samples, the less chance there is of the rate of acceleration actually changing enough to matter between those samples.
That program you posted, are you saying that it's working, it's just that you can't get a decent output from it? Not large enough or what? Not 'sensitive' enough?
I just did a bit of math. Apparently, at .66mv/deg/sec, with a 10bit A/D on the PIC (5v Vref = 4.8828125mv/bit), the lowest rate you'll be able to detect would be 7.4deg/sec.
Maybe you should change your +Vref and -Vref.
How about a resistive divider running off the 5v/Ground rail. Get 3 resistors that are almost EXACTLY the same. That should be able to get you down to 2.46deg/sec.
And you could do that all day, but then you run into the problem of range. You can have one but not the other.
I think a better fix for this might be to go with an A/D with more BITS! Maybe an external 16 bit A/D (if not more!).
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