unable to start service intent : not found
<p>I used AlarmManager to call up an activity every interval, however, the interval must can be changed. The activity is just a another function that I have changed into pendingIntent. 
The calling class is shown  below, which is also the main class. The called class is shown after the calling class. At the end , is the manifest file, which might contain the source of error.</p>

<pre><code>  Timer_test:

  package com.timer_test;

  import android.app.Activity;
  import android.app.AlarmManager;
  import android.app.PendingIntent;
  import android.content.Intent;
  import android.os.Bundle;
  import android.os.SystemClock;
  import android.view.View;
  import android.view.View.OnClickListener;
  import android.widget.Button;

 public class Timer_testActivity extends Activity {
  /** Called when the activity is first created. */

   private PendingIntent mAlarmSender;
   int update_freq = 1;
   Intent toast_make;
   int interval;

   @Override
   public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button button1 = (Button)findViewById(R.id.button1);
    Button button3 = (Button)findViewById(R.id.button3);
    Button button5 = (Button)findViewById(R.id.button5);
    Button button10 = (Button)findViewById(R.id.button10);

    toast_make = new Intent("com.timer_test.toast_testClass");
    mAlarmSender = PendingIntent.getService(Timer_testActivity.this, 0, toast_make           ,0);

    button1.setOnClickListener(new OnClickListener(){
        public void onClick(View arg0){
            update_freq = 1;
            timer_schedule();
    }
    });

    button3.setOnClickListener(new OnClickListener(){
        public void onClick(View arg0){
            update_freq = 3;
            timer_schedule();
    }
    });

    button5.setOnClickListener(new OnClickListener(){
        public void onClick(View arg0){
            update_freq = 5;
            timer_schedule();
    }
    });

    button10.setOnClickListener(new OnClickListener(){
        public void onClick(View arg0){
            update_freq = 10;
            timer_schedule();
    }
    });
}

  public void timer_schedule(){

    long firstTime = SystemClock.elapsedRealtime();

    interval = update_freq*1000;
    AlarmManager am = (AlarmManager)getSystemService(ALARM_SERVICE);
    am.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, firstTime, interval,    mAlarmSender);

}

 package com.timer_test;

 import android.app.Activity;
 import android.os.Bundle;
 import android.widget.Toast;

 public class toast_test extends Activity{

public void onCreate(Bundle icicle){
    super.onCreate(icicle);
    setContentView(R.layout.main);

    onClick("yes");
}

public void onClick(String n) {
    Toast.makeText(toast_test.this,n,
        Toast.LENGTH_SHORT).show();
     }

     }


    &lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.timer_test"
  android:versionCode="1"
  android:versionName="1.0"&gt;
  &lt;uses-sdk android:minSdkVersion="8" /&gt;

&lt;application android:icon="@drawable/icon" android:label="@string/app_name"&gt;
    &lt;activity android:name=".Timer_testActivity"
              android:label="@string/app_name"&gt;
        &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.MAIN" /&gt;
            &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
        &lt;/intent-filter&gt;
    &lt;/activity&gt;

    &lt;service android:name="com.timer_test.toast_test"/&gt;

  &lt;/application&gt;
 &lt;/manifest&gt;
</code></pre>
