Not only the sampling rate is off, but also the data are very
unreliable.
See my thread for our findings:
http://groups.google.com/group/android-developers/browse_thread/thread/f92f0d648a1c274f
If someone from google could comment, I am sure it would become clear
that cell phone is just that.
It will never match a real device at the cell phone's price, unless
poorly manufactured.
On Jul 9, 8:52 am, "House n @ MIT" <to...@mit.edu> wrote:
> Hello,
>
> Has anyone been able to get theaccelerometeron the G1 to sample
> consistently for long periods of time?
>
> We’ve been doing some testing of the G1accelerometeron Android, and
> wanted to see if others have gotten the same result. Our test uses a
> partial wake lock to keep the CPU alive. It stores the xyz values and
> time to local storage and then writes them to a file on the SD card
> once a second. The code below produces a csv file.
>
> The xyz values we’re getting are within the expected range, but the
> sample rate of theaccelerometervaries greatly. To determine that
> using the file produced, for each sample, we found the difference
> between the sample’s timestamp (taken from the SensorEvent) and the
> timestamp from the previous sample. The test results showed the time
> between samples ranging from 30 milliseconds up to 4.6 second
> spikes.
>
> We’re interested to know if other people are seeing similar behavior
> from their phones. If you have the time and means, please run the
> code below and post your results.
>
> Thanks
>
> package edu.acceltest;
>
> import java.io.File;
> import java.io.FileNotFoundException;
> import java.io.FileOutputStream;
> import java.io.PrintWriter;
> import java.util.Arrays;
> import java.util.List;
> import java.util.Timer;
> import java.util.TimerTask;
>
> import android.app.Activity;
> import android.content.Context;
> import android.hardware.Sensor;
> import android.hardware.SensorEvent;
> import android.hardware.SensorEventListener;
> import android.hardware.SensorManager;
> import android.os.Bundle;
> import android.os.PowerManager;
>
> public class AccelTest extends Activity {
>
> private SensorManager mSensorManager;
> private PowerManager.WakeLock mWakelock;
> private PowerManager mPowerMgr;
>
> @Override
> public void onCreate(Bundle savedInstanceState) {
> super.onCreate(savedInstanceState);
> setContentView(R.layout.main);
>
> // Set up theaccelerometerreading
> mSensorManager = (SensorManager)getSystemService
> (Context.SENSOR_SERVICE);
> // Get the list of all sensors, and find theaccelerometer
> within
> List<Sensor> sensorList = mSensorManager.getSensorList
> (Sensor.TYPE_ACCELEROMETER);
>
> mSensorManager.registerListener(mSensorListener,
> sensorList.get(0),
> SensorManager.SENSOR_DELAY_GAME);
>
> mPowerMgr = (PowerManager)getSystemService(POWER_SERVICE);
> if (mWakelock == null)
> {
> mWakelock =
> mPowerMgr.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK
> ,
> "Test");
> mWakelock.acquire();
> }
>
> }
>
> @Override
> public void onDestroy() {
> if (mWakelock.isHeld())
> mWakelock.release();
>
> }
>
> //Accelerometer
> private final SensorEventListener mSensorListener = new
> SensorEventListener() {
>
> private PrintWriter mCurrentFile;
> private Timer second = null;
> boolean never = true;
> String comma = new String(",");
> volatile int index = 0;
> float zam[] = new float[2000];
>
> public void runOnce()
> {
>
> //Creating a file to print the data into
>
> String nameStr = new String("/sdcard/Activity - game
> cached.csv");
> File outputFile = new File(nameStr);
> mCurrentFile = null;
> try {
> mCurrentFile = new PrintWriter(new
> FileOutputStream(outputFile));
> } catch (FileNotFoundException e) {
> // TODO Auto-generated catch block
> e.printStackTrace();
> }
>
> // Create a 1-second timer to check the sample rate
> second = new Timer();
> second.scheduleAtFixedRate(new TimerTask() {
>
> @Override
> public void run() {
>
> // dump to file and reset
> index, eventually overwriting all the
> data
> System.out.println("Sending");
> int a = 0;
> while(true)
> {
> if (zam[a*4] == 0)
> break;
> StringBuffer buff =
> new StringBuffer();
>
> buff.append(String.valueOf(zam[a * 4]));
> buff.append(comma);
>
> buff.append(String.valueOf(zam[a * 4 + 1]));
> buff.append(comma);
>
> buff.append(String.valueOf(zam[a * 4 + 2]));
> buff.append(comma);
>
> buff.append(String.valueOf(zam[a * 4 + 3]));
>
> mCurrentFile.println(buff.toString());
> a++;
> }
> mCurrentFile.flush();
> index = 0;
> Arrays.fill(zam, 0, 1999, 0);
> }
>
> }, 1000, 1000);
>
> }
>
> @Override
> public void onAccuracyChanged(Sensor sensor,
> intaccuracy) {
> // TODO Auto-generated method stub
>
> }
>
> @Override
> public void onSensorChanged(SensorEvent event) {
>
> if (never)
> {
> never = false;
> runOnce();
> }
>
> zam[index] = event.timestamp;
> zam[index + 1] = event.values[0];
> zam[index + 2] = event.values[1];
> zam[index + 3] = event.values[2];
>
> index += 4;
>
> }
> };
>
>
>
> }
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