USB OTG : Create your own cable

First of all, we need to understand what is USB OTG (On The Go). USB OTG is a protocol which enables electronic gadgets (such as mobile phones, cameras, pen drives) to communicate with each other through USB. As you would understand normally these gadgets get connected to a computer (which is called a 'host') as a peripheral (which is called a 'slave').

But in the USB OTG; some of these gadgets (which would normally play the role of 'slave') can act as 'hosts' for other gadgets.

Now a problem arises. How does a gadget (such as your smart phone) get to know the role which it needs to play (ie should it play as the host or the slave)? To answer this problem, we need to look at the pin assignment in a USB port.

A USB cable has 4 wires. 1 pair for power and another pair for data. But if you observe a mini or micro USB port which comes in a gadget like a phone or a camera, you will notice that there are 5 pins in the port. Apparently one pin is extra. That extra pin which happens to be the 4th pin (in between ground and data- pins) is the key.

If the extra (4th pin) is kept unconnected, the gadget will assume the role of the slave. This is the way a phone connects with a PC. If the 4th pin is connected to ground, the gadget assumes the role of host. This is how you need to connect a phone(host) with a pen drive (slave).

Now another important question, why do we need to create a DIY USB OTG cable? Number of mobile phones supporting USB OTG is very low. Also the number of users who are aware of USB OTG facility is even lower. Further many phone manufacturers do not not provide an OTG cable with the phone itself. Therefore it is very difficult to find a USB OTG cable in Sri Lankan market. As per my understanding only Nokia agents have this cable in their head office store at a very inflated price of about Rs 2000. But from Fort you can buy a normal USB micro (data) cable for Rs 200 and a normal USB (Regular) extension cable for Rs 100. Then you can make a USB OTG cable with only Rs 300 and litle bit of labour.

Therefore simply what we need to do in order to make a USB OTG cable out of a normal USB micro cable and a USB extension cable is

1. Crack open a micro USB connector and connect 4th (extra pin) and 5th (ground pin) pins.
2. Replace the male USB connector with a female one so that gadgets like pen drives can be connected (We need the the regular USB extension cable to salvage the female connector)

Now connect your smart phone with pen drive or other gadget and enjoy. By the way, did I mention that, your smart phone should support USB OTG?

Perfect java IDE for beginners

We have many java IDEs. Netbeans, Eclipse, IntelliJ being the most popular.

I'm an ardent netbeans follower. But there was a pressing problem in my mind about IDEs. What is the best IDE for a beginner; for a person who learns java?

The problem with Netbeans, Eclipse and IntelliJ is that they are meant for adavanced programmers. They are production tools and not learning tools.

1. They have cool yet 'not good for beginner' features like code completion
2. They have a rather complicated 'project structure' for the code. In other words they are not meant to write small 1 page, 1 file programs.
3. They are huge programs

Other option for the beginner is to program using a text editor, compile via command line. This is good but the beginner need to learn more 'techy' stufff like command line args, vim etc. This is very troublesome for the teacher.

So what we need a bare bone level IDE which

1. Does not have code completion and support
2. Facilitates writing short 1 page, 1 file programs without a complicated project structure.
3. Can compile the code with a single click
4. Should be smaller in size

Recently I came across 'Jcreator LE' which is free and crippled version. Yep that is crippled by removing features like code completion and that makes it the ideal IDE for learners.

VPN configurations for internet addicts

Preamble :

One of my friends have blogged on how he managed to connect via VPN and to generic internet in parallel.

http://tdevinda.blogspot.com/2009/11/whats-inside-what-virtualization.html

This ended up in bringing a nice discussion on routing, VPN and VMs.

Following is my solution.


Issue :

Under normal conditions; when you get connected to a VPN, it is not possible to get connected with the internet.

Reason:

When you get connected to the VPN, automatically it is set as the default route.


Solution:

1. Once you are connected to VPN, remove the default route for VPN. Under linux vpn is normally tun0.
2. Then add a default entry for your usual network interface. (eth0, ppp0, etc)
3. Then add the routing entry for the specific IP or the subnet which you need to get connected through VPN for tun0

Installing IE 8

Installed IE 8 in my office pc. (Yes I do use Fedora in my laptop, but the PC at office is still windoz xp). I am an avid follower of firefox. But my job includes testing web pages in many browsers. Earlier I was using IE6. But it was a pain to use it as it had no tabs. So after putting it off for many months, finally I decided to have the plunge.

Installing was a pain. If I participated in testing IE8, I will never give OK for it. There are many improvements to be done.
1. Installing process is awfully lengthy. In fact, an OS can be installed within that time.
2. There is no progress bar in the installation dialog, only a scrolling green worm like bar. So you got no idea whether installtion is actually in progress or something has gone wrong and installer is not responding.

Functionality seems still OK. In fact I'm writing the blog, via IE8. :-)

Hats off for Linux

I decided to use Fedora in my Laptop. The biggest hindrence I had to shift to Fedora from Windoz is now solved. You can plug and play USB HSPA modems now. Now hassles, just plug it and it works, even faster than on windoz xp.

This facility is available in Fedora 11 and Ubuntu 9. Guess most of the new Linux like Oss should have this.

C++ with netbeans

Few steps should be followed to integrate C++ with netbeans in Windows

1. Download and install MinGW
2. Download and install msys

• MinGW is the C/C++ compiler
• Msys is some kind of a unix emulator. After installing it and setting it in the path system variable, you can input unix commands such as mkdir, ls in the dos prompt. This is needed as makefile in C++ needs to access unix commands.

3. In the compile command dialog in netbeans provide the MinGW bin directory for base. Then it will identify C and C++ compilers other than the makefile. You need to provide the makefile.exe in msys/bin as the makefile location.

Then as the K&R said in their famouse C book, "if you have not botched anything, it should work" :-)

JSP importing class and jar files

Using java class files in jsp files

1. Put the class files in WEB-INF/classes/ folder

2. Import the class as <%@page import="."%>

3. Call that class as you would do in a normal java program

eg:

<%@page import="test.Hello"%>

<%
Hello heloo = new Hello();
String myName = heloo.SayName();
out.println("From scriptlet : "+ myName + "\n");
%>





Using a jar file in jsp

1. Put the jar file in lib folder.

2. Import the jar file as <%@page import=".*"%>

3. Call the class as .

eg:

<%@page import="jarTest.*"%>

<%
jartest.Main m = new jartest.Main();
String name = m.getName("Pinda");
out.println(name);
%>