Hello,
Has anyone been able to get the accelerometer on the G1 to sample
consistently for long periods of time?
We’ve been doing some testing of the G1 accelerometer on 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 the accelerometer varies 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 the accelerometer reading
mSensorManager = (SensorManager)getSystemService
(Context.SENSOR_SERVICE);
// Get the list of all sensors, and find the accelerometer
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, int
accuracy) {
// 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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