I am using LIS2DW12 Accelerometer for tilt angle detection
I can now get a interrupt trigger from the accelerometer when it crosses the threshold value given in the WAKE_UP_THS register in one direction(either clockwise or counter clock wise).
Is it possible to detect the tilt angle in both directions and trigger the interrupt event in wakeup interrupt mode?
It is possible in 6d orientation mode, but I need wakeup interrupt mode since I have to detect the tilt angles from 10 degrees.
Please suggest a suitable solution.
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I am currently developing an App which should calculate the speed by the accelerations of the device. To achieve this I am using Sensing Kit. The app records data of the users motion and saves it to the local storage. When the user stops the recording it is possible draw the collected accelerations in velocity by time (Three graphs for every axis of the accelerometer).
Sensing Kit uses startAccelerometerUpdates of the CMMotionManager to get the accelerations. To calculate the velocity I do some signal processing and an integration of the acceleration (and multiply it by 9.81 because apple measures the acceleration in increments of gravity). The result is the velocity over the recorded time (Its not very precise but that doesn't matter in my case).
I tested my app by sliding the phone over a table with the screen up and the upper screen side in moving direction. The movement later shown up in the resulting graph of Y-Axis, but it has a negative velocity (The accelerations are negative, too). I expect that the velocity and the acceleration should be positive, because I moved the device in the positive direction of the Y-Axis.
The same happens with the X-Axis wehen I move the phone on the table in the direction of this axis.
I tested it today without Sensing Kit and get same results.
The gravity is always as I expect a negative velocity on the z-Axis, because its an acceleration to the ground.
Can somebody explain to me why the acceleration of the sensor has the wrong sign?
Thank you.
https://developer.apple.com/documentation/foundation/unitacceleration
https://developer.apple.com/documentation/foundation/units_and_measurement
The Foundation library has a function for this and you could use this to convert between UnitAcceleration and UnitSpeed.
I'm new to Core Motion and I'm very confused. Can somebody please explain what these inputs measure and how they can be useful in simple terms?
Accelerometers measure movement relative to gravity, by virtue of "feeling" the force of movement applied to the device. Force of movement can be described as the rate of acceleration and deceleration of the device, hence the name of this sensor.
Gyroscopes measure changes in rotation by virtue of a suspended element reporting its rotation relative to the device. As the device rotates, this suspended element doesn't rotate, so there's a report coming from it that tells you how far the phone's rotated.
Magnetometers get their idea of rotational position from the north/south magnetic fields that compasses use to know where they are relative to the poles. This data is used (primarily) to help the Gyroscope, because these things suffer from float and inertia.
Combined, the information from these sensors, when filtered well (which Apple does for you with CoreMotion) give you all the movement of a phone.
So you can know if the user is swinging the phone around like a table tennis bat, or steering like a Wii Remote Mario style game controller, or simply walking.
In iOS, it is easy to access Linear Acceleration which is equal to subtracting Gravity from Raw acceleration.
I am trying to estimate position by double integrating Linear Acceleration. For that I recorded the data by keeping the phone steady on table.
Then I did double integration in Matlab using cumtrapz but when I plot the position it grows with time.
What am I doing wrong? I was expecting that the position should be 0.
From what I've read this is too error-prone to be useful. Accelerometer based position calculations are subject to small drift errors, which accumulate over time. (If the phone is traveling at 100 kph constant velocity when your app first launches, you can't tell.) All you can measure is acceleration.
There would always been biasing errors from the sensors which can grow with time while integration. Can you calculate the drift of sensor when the device is at rest?. And then try to take the mean of the drift and subtract it from the input so that sensor shows 0 at rest, Then try to double integrate it
I'm making an app in which the user can move their devices left, right, up, and down in order to view an image. The way I'm doing this is by reading in the accelerometer data to calculate how far in each direction the user moved the device. The issue is that these readings are heavily influenced by the tilt of the device, because the axis change slightly with every tiny tilt. I know the gyroscope measures the rotational accelerations, so is there a way I could use those readings to take tilt out of the picture and fix the axis so they are the same at whatever angle the user holds the device? I realize this is a very eloborate problem, so if you don't understand something feel free to ask
Iphone accelerometer provides user acceleration and gravity reading? It's clear from the apple guide the user acceleration means, the acceleration than the phone get's from the user. Then what is the meaning of gravity reading? Anyway they have mention total acceleration is the addition of both! I m confused with gravity reading, Can anyone explain me the theory behind this?
Thank you in advance!
The accelerometer measures the sum (user acceleration + gravity). Unfortunately it is of little use, in your application you typically need one or the other. So it is split into components (into user acceleration and gravity) with a sophisticated procedure called sensor fusion.
Gravity points downwards, corresponds to the gravitation. It tells you where downwards is. You can compute tilt angles from it, which may be handy in developing tilt games.
The user acceleration is handy when you are trying to figure out how the phone is shaken. It good for shaking games.
See also accelerometers uses- smartphone
Gravity is an acceleration which is constant an downward. It is indistingishable along its vector from any other constant acceleration. Rotating the phone is going to change the contribution of gravity to each of the acceleration axis proportionate to angle with the ground. Gravity being constant, any change in combined vector length of the three axis should be due to user acceleration.