Accelerometer’s frequency on Android with code

English text

Some values for accelerometer’s frequency

After researchs on the Internet with my friend Google, as I did not find out the frequency of Samsung Galaxy S2 Accelerometer on Android, I decided to build my own code to know the frequency !

On Android, you can use one of the four next rates for the accelerometer :

1. FASTEST
2. GAME
3. NORMAL
4. UI

Get accelerometer's frequency on android

On my Galaxy S2, I get the next frequencies for the accelerometer :

1. FASTEST    : 100 Hz
2. GAME          : 50   Hz
3. NORMAL    : 5      Hz
4. UI                 : 16    Hz

This the Java code to test the frequency of your accelerometer. You can also download all the code and import the project in Eclipse for example.

Code

package samoht.tuto.frequency;
import android.app.Activity;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
/**
 *
 * @author Samoht
 * http://samoht.fr
 * Do what you want with this code, if you let this disclaimer
 * 19/11/2011 18:00
 *
 */
public class GetFrequencyActivity extends Activity implements SensorEventListener {
	private static final double nbElements = 30;
	private SensorManager sensorManager;
	private Sensor accelerometer;
	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
		boolean accelSupported = sensorManager.registerListener(this,
				sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_UI);
		accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
		if (!accelSupported) {
			sensorManager.unregisterListener(this, accelerometer);
			((TextView) findViewById(R.id.acc)).setText("Accelerometer not detected");
		}
	}
	/**
	 * Always make sure to disable sensors you don't need, especially when your
	 * activity is paused. Failing to do so can drain the battery in just a few
	 * hours. Note that the system will not disable sensors automatically when
	 * the screen turns off.
	 **/
	protected void onResume() {
		super.onResume();
		sensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_UI);
	}
	protected void onPause() {
		super.onPause();
		sensorManager.unregisterListener(this);
	}
	protected void onDestroy() {
		super.onDestroy();
		sensorManager.unregisterListener(this);
	}
	@Override
	public void onAccuracyChanged(Sensor sensor, int accuracy) {
		// Nothing to do
	}
	long now = 0;
	long time = 0;
	int temp = 0;
	@Override
	public void onSensorChanged(SensorEvent event) {
		long tS;
		// only if the event is from the accelerometer
		if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
			float x, y, z;
			x = event.values[0];
			y = event.values[1];
			z = event.values[2];
			// Get timestamp of the event
			tS = event.timestamp;
			((TextView) this.findViewById(R.id.axex)).setText("X : " + x);
			((TextView) this.findViewById(R.id.axey)).setText("Y : " + y);
			((TextView) this.findViewById(R.id.axez)).setText("Z : " + z);
			// Get the mean frequency for "nbElements" (=30) elements
			if (now != 0) {
				temp++;
				if (temp == nbElements) {
					time = tS - now;
					((TextView) findViewById(R.id.acc)).setText("Frequency : " + (nbElements * 1000000000 / time)
							+ " Hz");
					temp = 0;
				}
			}
			// To set up now on the first event and do not change it while we do not have "nbElements" events
			if (temp == 0) {
				now = tS;
			}
		}
	}
	public void onClickQuit(View v) {
		finish();
	}
}

Remarks

If you want to limit the number of digits in the frequency, use a mask :

	String mask= new String("#0.##");
	DecimalFormat form = new DecimalFormat(mask);
        ...
((TextView) findViewById(R.id.acc)).setText("Frequency : " + form.format(<code>nbElements </code> * 1000000000 / time) + " Hz");
....

Then, if you want a more precise frequency,change the value of nbElements. Instead of 30, set 50 or 100. The greater the number is, the slower the refresh time is.

Other usefull information, the timestamp is in nanosecond, that’s why I multiplie by 10 to power of 9, to change the result in seconds.

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