Android - Acceleration Down (Smash)

Android - Acceleration down (smash)

A stationary device will have an gravity value of +9.81, which corresponds to the acceleration of the device (0 m/s2 minus the force of gravity, which is -9.81 m/s2). Thus if the device is moving downward from stationary then the gravity will be less than 9.81. A free fall device will have gravity equals 0.

Below is how to determine if the device starts moving downward. It will not be able to determine whether the device is moving downward if the device is already moving downward with constant speed, since in this case there is no acceleration downward and the gravity norm should be around 9.81.

You need to use TYPE_GRAVITY. If the device does not have TYPE_GRAVITY, then low pass filter TYPE_ACCELEROMETER to get the gravity vector.

As above a stationary device will have a gravity vector with norm equal 9.81. However, this value will vary slightly with devices. Thus you need first to determine this stationary gravity norm. You can do this by register for TYPE_GRAVITY or TYPE_ACCELEROMETER and ask the user to lay the device flat and then press a button. Once the button is pressed the app will calculate the norm of the gravity in onSensorChanged.

private float mStationaryGravityNorm;
private float mDeviation = 0.01;
private float mCount;
private boolean mIsCalculatingStationGravityNorm = true;

Button button = findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener( {
    @Override
    public void onClick(View v) {
        // register sensor
    }
    });

@Override
public void onSensorChanged(SensorEvent event) {
// Will average out 100 gravity values.
if (mIsCalculatingStationGravityNorm) {
    if (mCount++ < 100) {
        mStationaryGravityNorm += Math.sqrt(event.values[0] * event.values[0] + event.values[1] * event.values[1] + event.values[2] * event.values[2]);
    } else {
        mStationaryGravityNorm /= 100;
        mIsCalculatingStationGravityNorm = false;
} else {
    float gravityNorm = Math.sqrt(event.values[0] * event.values[0] + event.values[1] * event.values[1] + event.values[2] * event.values[2]);
    if (gravityNorm < mStationaryGravityNorm - mDeviation) {
    // moving down
    }
}

PS For moving up an down you do want to calculate gravity. When the device is stationary, the gravity norm is approximately 9.81 (depending on device). Now if the device is moving down, there is an acceleration downward, thus the gravity norm will be less than 9.81 and if the device is moving up the gravity norm will be more than 9.81. So by comparing the gravity norm against this stationary gravity norm, you will know if the device moving up or down. This is independent of the device orientation. TYPE_GRAVITY will give better accuracy but if the device does not have this type then low pass filter TYPE_ACCELERATOR will give you the gravity vector.

Android: Accelerometer false detection

Here are a few code discrepancies...

• There may be a problem regarding the updating of last_x, last_y, and last_z. I believe they should be included inside the if ((curTime - lastUpdate) > 100) { statement. In other words, they are being updated every time onSensorChanged is called, not every 100 milliseconds. You should probably move the updating of those three variables into the curly brace above them.

• On the line where you compute the speed, the formula ends with ... / diffTime * 10000; Are you wanting to multiply just diffTime by 10000, or the entire result? Since / and * typically have the same operator precedence in most languages I know of (such as Java), your equation will be evaluated from left to right, dividing first by diffTime then multiplying that result by 10000.

  I'm guessing you mean to multiply just diffTime by 10000, thus dividing the final result by that amount. This is the difference between dividing by 10000 or multiplying by 10000, which means you are probably getting values for speed that are 10^8 greater than you should, thus tripping your threshold even when the device is idle. You need to put parentheses around the multiplication, like ... / (diffTime * 10000);, to make sure it's performed before the division takes place.

  Additionally, if you are intending to scale diffTime from milliseconds to seconds, your scale factor should be 1000.

Moving an image using Accelerometer of android

Use this code. You were never setting the location of the drawable after you intialized that class. You'll have to do some calculations to set the balls location properly. The way you were doing it was getting values over 10000 which was drawing the oval off screen.

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;

public class Accelerometer extends Activity implements SensorEventListener
{
    /** Called when the activity is first created. */
    CustomDrawableView mCustomDrawableView = null;
    ShapeDrawable mDrawable = new ShapeDrawable();
    public static int x;
    public static int y;

    private SensorManager sensorManager = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {

        super.onCreate(savedInstanceState);
        // Get a reference to a SensorManager
        sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        mCustomDrawableView = new CustomDrawableView(this);
        setContentView(mCustomDrawableView);
        // setContentView(R.layout.main);

    }

    // This method will update the UI on new sensor events
    public void onSensorChanged(SensorEvent sensorEvent)
    {
        {
            if (sensorEvent.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
                // the values you were calculating originally here were over 10000!
                x = (int) Math.pow(sensorEvent.values[1], 2); 
                y = (int) Math.pow(sensorEvent.values[2], 2);

            }

            if (sensorEvent.sensor.getType() == Sensor.TYPE_ORIENTATION) {

            }
        }
    }

    // I've chosen to not implement this method
    public void onAccuracyChanged(Sensor arg0, int arg1)
    {
        // TODO Auto-generated method stub

    }

    @Override
    protected void onResume()
    {
        super.onResume();
        // Register this class as a listener for the accelerometer sensor
        sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
                SensorManager.SENSOR_DELAY_NORMAL);
        // ...and the orientation sensor
        sensorManager.registerListener(this, sensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION),
                SensorManager.SENSOR_DELAY_NORMAL);
    }

    @Override
    protected void onStop()
    {
        // Unregister the listener
        sensorManager.unregisterListener(this);
        super.onStop();
    }

    public class CustomDrawableView extends View
    {
        static final int width = 50;
        static final int height = 50;

        public CustomDrawableView(Context context)
        {
            super(context);

            mDrawable = new ShapeDrawable(new OvalShape());
            mDrawable.getPaint().setColor(0xff74AC23);
            mDrawable.setBounds(x, y, x + width, y + height);
        }

        protected void onDraw(Canvas canvas)
        {
            RectF oval = new RectF(Accelerometer.x, Accelerometer.y, Accelerometer.x + width, Accelerometer.y
                    + height); // set bounds of rectangle
            Paint p = new Paint(); // set some paint options
            p.setColor(Color.BLUE);
            canvas.drawOval(oval, p);
            invalidate();
        }
    }
}

My Application Crashes when I Register a Sensor Listener

mContext is null - you need to initialise it before you pass it to Toast.makeText().

Service is a context so you can just call

Toast.makeText(this,"Heelooo" , Toast.LENGTH_SHORT).show(); 

It works when you remove the lines you mention because then the SensorListener is never registered, and onSensorChanged is never called.

Android - How to approach fall detection algorithm

First, I want to remind you that you cannot just add the x, y, z values together as they are, you have to use vector mathematics. This is why you get values of over 15 m/s. As long as the phone is not moving, the vector sum should always be about 9.8 m/s. You calculate it using SQRT(x*x + y*y + z*z). If you need more information, you can read about vector mathematics, maybe http://en.wikipedia.org/wiki/Euclidean_vector#Length is a good start for it.

I also suggest another algorithm: In free fall, all three of the x,y,z values of the accelerometer should be near zero. (At least, that's what I learned in physics classes a long time ago in school.) So maybe you can use a formula like if the vector sum of x,y,z <= 3 m/s than you detect a free fall. And if the vector sum then raises to a value over 20 m/s, than you detect the landing.

Those thresholds are just a wild guess. Maybe you just record the x,y,z values in a test application, and then move around the phone, and then analyze offline how the values (and their normal and vector sum) behave to get a feeling for which thresholds are sensible.

Which android sensor will give ma data if I move phone like this...?

You need Acceleration sensor and Orientation sensor as well to accuratelly recognize the move described in your video.

So, I would recommend to collect the data from mentioned sensors and describe movement (acceleration and orientation should have separate 3D functions) with few mathematical functions/graphs. Then , within certain accuracy, check whether repeated move matches expected behaviour on all axis.

You will need this for reference on the axis:

http://developer.android.com/reference/android/hardware/SensorEvent.html

Looks like no change (or very small) should occur on Y-axis to describe move from your video.

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