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Monitor the free fall detection and calculate gravitational force

Thread starter #1
I am using the accelerometer to detect the vibration but at the same time, I need to test the free-fall detection using wireless sensor with Arduino https://store.ncd.io/product/mma766...-sensor-±1-5-g-accelerometer-i2c-mini-module/ and perform some different functions with relay board but before that I need to know if anyone can help me how can I be able to find the free-fall detection as well as gravitational force of the object. Any kind of useful suggestion to make it work will be very helpful
 

dknguyen

Well-Known Member
Most Helpful Member
#2
in free fall all axis will read zero, plus the inaccuracies of the accelerometer. So just read the value and check to see if all axises are near zero before trying to do anything else with it.

probably want to filter the signal from DC before using it for vibration, but only after checking for free fall.
 
Thread starter #3
Thanks for the reply, I tried this way but still values are not similar, any good way to just check the freefall by just checking 0 or 1 value ??
 

alec_t

Well-Known Member
Most Helpful Member
#4
I'm not sure I believe the write-up of that module, where it states "detect quick motion pulses as single-taps, double-taps, and 0g (free-fall) conditions on any or all axis". Surely free fall = 1g (on planet Earth)?
It's my understanding that most accelerometer modules can sense positive or negative acceleration and 0g would give a non-zero output on at least one axis.
 

dknguyen

Well-Known Member
Most Helpful Member
#5
Thanks for the reply, I tried this way but still values are not similar, any good way to just check the freefall by just checking 0 or 1 value ??
That is something the module would have to provide and I did not see it in the datasheet.

When you say "the values are not similar" how similar is not similar?

I'm not sure I believe the write-up of that module, where it states "detect quick motion pulses as single-taps, double-taps, and 0g (free-fall) conditions on any or all axis". Surely free fall = 1g (on planet Earth)?
It's my understanding that most accelerometer modules can sense positive or negative acceleration and 0g would give a non-zero output on at least one axis.
Are you talking about acceleration as measured by an observer external to the accelerometer? Or within the reference frame of the accelerometer itself?
 

alec_t

Well-Known Member
Most Helpful Member
#6
I was referring to the accelerometer's reference frame.
 

JonSea

Well-Known Member
#7
Yes, in free fall, the accelerometer normal to the ground will experience 0 g. The blue line on this plot is the axis normal to the ground, initially showing 1 g as it's (mostly) stationary about 3' above my bed. The step to zero is when I released it and it was in free fall. The big extremes in all axes is when it hit my bed.

SmartSelect_20180824-122028_Sensor Kinetics.jpg
 

JonSea

Well-Known Member
#8
The power in a modern phone is beyond belief. What used to be a rather complex measurement task done in 30 seconds.
 

dknguyen

Well-Known Member
Most Helpful Member
#10
I was referring to the accelerometer's reference frame.
Yeah, so in free-fall the accelerometer will register 0G because the beam inside is not deflected with respect to the frame of accelerometer because both beam and frame are accelerating at 1G downwards.
 

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