Accelerometer readings

Questions and discussion about running MicroPython on a micro:bit board.
Target audience: MicroPython users with a micro:bit.
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thechymist
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Joined: Thu Feb 04, 2021 8:03 pm

Accelerometer readings

Post by thechymist » Thu Feb 04, 2021 8:12 pm

I am trying to program the microbit to measure g by having one act as a falling object and another to log the data. I have got the two of them communicating and got data, but I don't understand the values. Why when my microbit is stationary do i get a z reading of approx -1g? Surely when stationary the acceleration is 0? If the -1000 represents the force due to gravity, why does it go up to a positive value when falling? My expectation was that either it would start at 0 and go to +980 ish whilst falling, or start at +980 ish and then fall to 0 in freefall, but neither seems the case

If anyone can help me with how the accelerometer readings actually work then i would appreciate it

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jimmo
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Re: Accelerometer readings

Post by jimmo » Mon Feb 08, 2021 6:55 am

thechymist wrote:
Thu Feb 04, 2021 8:12 pm
Why when my microbit is stationary do i get a z reading of approx -1g? Surely when stationary the acceleration is 0?
https://en.wikipedia.org/wiki/Equivalence_principle

Being "stationary" in a gravitational field is equivalent to being in an accelerating rocket in empty space.
thechymist wrote:
Thu Feb 04, 2021 8:12 pm
If the -1000 represents the force due to gravity, why does it go up to a positive value when falling?
What sort of positive values do you see? While the device is truly in freefall, (i think) you should see values close to zero.

When the device hits the ground you will see positive values as it decelerates.

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