FFT based simple Spectrum Analyzer

i am writing this blogpost to pay homage to my alma mater... i was not at my level best to understand all aspects of Electonics & Telecommunication, the Microprocessor, the Digital Communication, the Digital Signal processing as taught by my professors... however, after so many years while playing around with different software, i understand how valuable was their contribution to make me an engineer. i remember, how important was the lesson of digital communication, and digital signal processing taught by Dr. T.K.Sen... i remember how important was the lesson of Microprocessor taught by A.R.... i remember how important was the lectures of Maths during our engineering course... i remember how important were the concepts of Fourier Transformation, FFT, DFT, Laplace Transformation, Matrix algebra and Complex Algebra...Hats off to all those professors who in spite of all odds helped a small town boy see the outer world...

Here goes the apk of my FFT based simple Spectrum Analyzer for an Android device with a sampling frequency of 8 KHz and audio encoding as 16 bit PCM...

i was so excited when i finished the coding part (of course with the help of Google...) and saw its working on a real device...

here are the two screenshots i have taken from an Android device...

How to set up proxy for Android emulator behind a firewall...

Here is how i had set up my emulator's network settings for browsing the internet on a Windows 7 machine. for linux the same principle applies...

• Make the emulator pass through the firewall
• if you are behind a proxy go to settings and set up your proxy for the emulator through the following steps-

1. Open the emulator and click on Menu
2. Click on Settings
3. Click on Wireless & Networks
4. Go to Mobile Networks
5. Go to Access Point Names and click on it
6. Click on Telkila Internet
7. In the Edit Access Point, input Proxy server and Port
8. Also provide the User Name and Password
9. Keep rest of the fields blank

• Sometimes the DNS of the host PC is not recognized by the emulator...  in that case use the following command in the command prompt...emulator -avd -dns -server 8.8.8.8 (8.8.8.8 is the Googles default DNS) and change the DNS server of your machine to 8.8.8.8. otherwise you may opt for the DNS your company is using in the emulator -avd -dns -server command...

Hope this discussion comes handy for the Android newbies...

An implementation of Finite State Machine in Android using Handler...

As i was doing some research on different concepts in Android, i came out with this implementation of Finite State Machine using the Handler class... i would like to share it with you... the state diagram of the application will look as the following:

The main Activity class looks like the following:

package com.android.training.statepattern;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;



public class StatePatternActivity extends Activity implements View.OnClickListener{
private Button startStatePattern;
private MyHandler handler;
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
       
       startStatePattern = (Button)findViewById(R.id.button1);
       
       startStatePattern.setOnClickListener(this);
       handler = new MyHandler(this);
   }
   
   public void onClick(View v){
    if(v.equals(startStatePattern)){
    handler.sendEmptyMessage(1);
    }
   }  
}

And the other class is as follows;

package com.android.training.statepattern;

import android.os.Handler;
import android.os.Message;
import android.widget.Toast;

public class MyHandler extends Handler {
private StatePatternActivity MainActivity;

MyHandler(StatePatternActivity a){
this.MainActivity = a;
}
//state transition logic is strongly coupled with the different states...
public void handleMessage(Message msg){
switch(msg.what){
case 1:
////do the processing
Toast.makeText(MainActivity.getApplicationContext(),"Inside State 1", 2000).show();
this.sendEmptyMessage(2);
break;
case 2:
///do the processing
Toast.makeText(MainActivity.getApplicationContext(),"Inside State 2", 2000).show();
this.sendEmptyMessage(3);
break; case 3:
///do the processing
Toast.makeText(MainActivity.getApplicationContext(),"Inside State 3", 2000).show();
this.sendEmptyMessage(4);
break;
case 4:
break;
default:
break;
}
}
}

Let me explain the code a bit... here the crux of the solution lies in the MyHandler class derived from Handler.. The main activity class HAS MyHandler..

We start the State machine by sending a message (integer 1) through the function SendEmptyMessage called on MyHandler object. As a result, the callback function called handleMessage of the Handler is called and we handle this state's functionality here... the next all starte transitions happen sequentially from this callback function...

Hope this throws some lights on a specific design concept in Android...

Robotium - automated unit test tool for Android...

the following text explains how to use Robotium in Eclipse.. Robotium is an automated unit testing tool for Android...

for this we need to download the Robotium.jar file from here...
setting up the environment is easy...

• put the above jar in the build path’s library section...

• add the following lines of code in the manifest.xml file in the manifest section (i.e. outside the app section)...

(instrumentation android:name="android.test.InstrumentationTestRunner"
   android:targetPackage="training.android.trainingunitconverter"
   android:label="1" /)

the below snippet of code is to test the UnitConverter app...

• create a file(say UnitConverterTest.java) and add the following piece of code...

package training.android.trainingunitconverter;


import java.util.ArrayList;
import android.test.ActivityInstrumentationTestCase2;
import android.test.suitebuilder.annotation.Smoke;
import android.widget.EditText;
import android.widget.Spinner;
import com.jayway.android.robotium.solo.Solo;

public class UnitConverterTest extends ActivityInstrumentationTestCase2{
private Solo solo;
public UnitConverterTest() {
super("training.android.trainingunitconverter", UnitConverter.class);
}
public void setUp() throws Exception {
solo = new Solo(getInstrumentation(), getActivity());
}
@Smoke
public void testUnitDropDown() throws Exception {

solo.assertCurrentActivity("Expected UnitConverter activity", "UnitConverter");
solo.pressSpinnerItem(0, 1);
solo.sleep(2000);
EditText value = (EditText)solo.getView(R.id.EditTextValue);
solo.enterText(value, "1");
solo.pressSpinnerItem(1,0);
solo.sleep(1000);
solo.pressSpinnerItem(2,1);
solo.sleep(1000);
solo.clickOnButton(0);
assertTrue(solo.searchText("1000.0"));
}
@Override
public void tearDown() throws Exception {
//Robotium will finish all the activities that have been opened
solo.finishOpenedActivities();
}
}

however, it seems that the solo.PressSpinnerItem() is not functioning properly on the emulator (either Android 2.2 or Android 1.6)... hopefully this issue will be fixed in the next release of Robotium...

to run it in the emulator, right click on the Project... go to Run As.. and press  Android JUnit Test...

the screen shot for the above test condition is 

as from the test case
@Smoke
public void testUnitDropDown() it is clear, that we are first asking the test framework to select the item having index 1 (that is Weight) from the first spinner. then we are asking the framework to put a value 1 in the edittext. we are then asking the test framework to select item with 0th index (that is Kg) from the second spinner and item with index 1 (that is gm) from the third spinner... and we are asking the framework to press Convert button... so the expected result will be 1000.0... and we search in the test case if it has the value 1000.0. then the test case will PASS …
similarly we can test different scenarios automatically by having more such functions as testUnitDropDown...


note:  the source code of the UnitConverter App can be cloned from https://github.com/sommukhopadhyay/UnitConverter

Git & GitHub

i think by now most of the people know about Git and Github. however, as i am still  not very much hands-on vis-a-vis contributing in the open source community, i think this piece of information will be useful to others...  

Git is an opensource version comtrol system developed by the same person who had created Linux. And using free version of Github, we can share our source code to the open source community. 

For this one will just have to open an account at www.github.com, create his own repository. However, to push your source code to this github repository, one has to install Git in the local machine. The latest version of eclipse comes with EGit plugin, which is of great help to push the project from the eclipse workspace.

i think its a good step towards contributing in the open source community...

here are the step by step screenshots of how one can push his project into the GitHub directly from the eclipse workspace...

                                                                           step1

                                                                            step 2

                                                                           step 3

                                                                         step 4

                                                                         step 5

                                                                            step 6

                                                                            step 7

                                                                          step 8

Handling exception at construction in C++ using Boost's shared_ptr

Its a very common problem in C++ that if a class's constructor throws an exception (say memory allocation exception) how we should handle it. Think about the following piece of code. Here class A's constructor has thrown an exception.. so the best way to handle such situation is to instantiate A inside a try block...if exception is thrown in the constructor of A, i will be destroyed by stack unwinding and the thrown exception will be caught... try-catch block in exception is very important as constructor cannot return anything to indicate to the caller that something wrong has happened...

#include (iostream)

#include (string)
#include (memory)

class MyException(string str){
private:

string  msg;

public:

MyException(string str){

msg = str;

}

void printerrmsg(){

cout((msg.c_str()((endl;

}

}

class A{
private: int i;

//if exception is thrown in the constructor of A, i will de destroyed by stack unwinding
//and the thrown exception will be caught
A()
{
i = 10;
throw MyException(“Exception thrown in constructor of A()”);

}

};
void main(){
try{

A();

}
catch(MyException& e){

e.printerrmsg();

}

}

now there is another point... suppose we need to allocate some dynamic memory in the constructor... and while doing that the constructor throws a memory exception... so the stack based pointer which was referencing the heap based memory will be destroyed because of the stack unwinding... so we will have some memory which is referenced by no pointer and hence we cannot access that... so obviously its a memory leak...  so, how can we handle that...

the best way to handle this kind of situation in modern C++ is to use auto_ptr/shared_ptr/shared_array ... so the solution will look something as the following:


#include (iostream)
#include (string)
#include (memory)
#include (boost/shared_ptr.hpp)
#include (boost/shared_array.hpp)



using namespace std;

class SomeClass{
public:
SomeClass(){}
~SomeClass(){};
};

typedef boost::shared_ptr(SomeClass) pSomeClass;
typedef boost::shared_ptr(char) pChar;
typedef boost::shard_array(char) charBuff;

class MyException{
public:
MyException(string str){
msg = str;
}
void printerrmsg(){
cout((msg.c_str()((endl;
}
private:
string msg;
};


class A{
private:
int i;
pChar m_ptrChar;
pSomeClass m_ptrSomeClass;
charBuff m_pcharBuff;

//if exception is thrown in the constructor of A, i will be destroyed by stack unwinding
//and the thrown exception will be caught
public:
A():m_ptrChar(new char),m_ptrSomeClass(new SomeClass),m_pcharBuff(new char[100])
{
i = 10;
throw MyException("Exception at A's constructor");
}
};


int main(){
try{
A objA;
}
catch(MyException& e){
e.printerrmsg();
}
return 1;
}

In Symbian C++, it is handled by a concept called two phase constructor... (it came into the picture because there was no template concept in earlier Symbian C++, and hence there was no auto_ptr)... in this process, if we want to create a dynamic memory allocation at the heap pointed by say *pMem, then in the first phase of construction we initialize the *pMem by NULL. obviously this cannot throw exception...then this pMem is pushed to a cleanupstack(this is something new in Symbian) so that we have a reference in the CleanupStack for future reference... and in the second phase of construction, we allocate memory pointed by pMem... so, if the constructor fails, we still have a reference of pMem in the cleanup stack... we just need to pop it and destroy it... hence there is no chance of memory leak...

hope this discussion comes handy for C++ learners...

How to launch an Android App from the Browser

As i was doing some experimentation with android, i tried to launch a native app from a browser link... and i was successful... i would like to share whatever i have done with you..

The first thing one has to do to launch an app from a browser’s link is to add an additional intent filter in the app’s  Manifest file... for example to launch my native app (called UnitConverter) i have added the following few lines in the App’s manifest...

                  <data android:scheme="unitconverter" />
                  <action android:name="android.intent.action.VIEW" />
                  <category android:name="android.intent.category.BROWSABLE" />
                  <category android:name="android.intent.category.DEFAULT" />

and in the web app i have added html code as (a href="unitconverter://")Launch UnitConverter App(/a)
and it has worked fine..
however, sometimes we may need to pass some query parameters in the html query tag like
(a href="unitconverter://?param1key=param1value&param2key=param2value)Launch UnitConverter App(/a)
to catch these query parameters inside the Android app, i have written the following piece of code and added it in the onCreate function of the main Activity just after the line super.onCreate(savedInstanceState).

//to get the parameter passed from the URI that has launched this app
    final Intent intent = getIntent();
    String scheme = intent.getScheme();
    if(scheme != null){
            final Uri myURI=intent.getData();
            String queryString = new String();
               
            if(myURI!=null)
            {
              queryString = myURI.getQuery();
            }
            String split1 = "&";
            String split2 = "=";
            
            if (queryString != null)
            {
                final String[] arrParameters = queryString.split("&");
                for (final String tempParameterString : arrParameters)
                {
                    final String[] arrTempParameter = tempParameterString.split("=");
                    if (arrTempParameter.length( )== 2)
                    {
                        final String parameterKey = arrTempParameter[0];
                        final String parameterValue = arrTempParameter[1];
                        //do something with the parameters
                        Toast.makeText(this, parameterValue, 500).show();
                    }
                }
            }    
    }

And voila!!! it has worked perfectly...
Hope this discussion comes handy for the Android learners...