Archive

Archive for the ‘Computers’ Category

Wireless on Asus X200M netbooks: Ubuntu 14.04 LTS

April 4th, 2016 Comments off

We resently bought several Asus X200 series netbooks for our faculty members. The main attraction of this  cute  netbook is its  light weight and a built in HDMI port. We plan to use them extensively for   content delivery in class rooms. These  machines are really cheap, costing around Rs17000 ( around $260).  The base model comes with Intel® Celeron® Dual-Core ~ 2.58 GHz Processor and 2GB ram, DOS operating system. It has an 11.6 inch LED display.

Our idea was to put   ubuntu 14.04 and deploy the machines. The machine has an ethernet port and wifi port.  Installation of Ubuntu 15.10 was a smooth affair.  Unfortunately, the broadcom wifi interface did  not work out of the box. Here is what I did to fix the issue.

  1. Find out which wifi chip is used.

$lspci broadcom wifi lspci

The wifi chip is  Broadcom Corporation BCM43142. You have to download and compile the kernel module for this chip.

2) Make sure that the machine is connected to internet and the apt sources are properly set up

3) Update  the machine

$ sudo apt-get update

4) Finally instal the  bcmwl driver.

$ sudo apt-get install linux-headers-`uname -r` dkms build-essential bcmwl-kernel-source

This will downlad necessary driver  your wifi will be up and running. The above line installs dynamic kernel module support  and compiles the broadcom wireless driver.

Categories: Computers, Gnu/Linux Tags:

ATU with REFLECTOMETER

July 2nd, 2011 Comments off

by  R. Jayaraman (VU2JN)

This article is a sequel to the article “A Compact ATU handles 100 watts” that was published online in March 2011. It describes a Norcal-type Antenna Tuning Unit with an in-line Stockton-bridge-type Reflected-power Indicator that I built recently (April 2011). This ATU is also capable of handling the full output of a 100-watt HF transceiver.

The ATU circuit is that of the well-known Norcal BLT ATU, with minor modifications. A Reflectometer, ie. reflected-power indicator, forms part of this ATU and makes it self-contained, obviating the need for a SWR bridge. It is based on the Stockton SWR bridge, an interesting bridge circuit using 2 toroidal RF pick-up coils. This circuit deserves to be used more commonly by hams. For those who are interested, additional details of the Norcal BLT ATU and the Stockton SWR Bridge are available on the internet.

Fig.1. Circuit diagram of the ATU with Reflectometer

The toroidal coil of the Norcal ATU has been replaced with an open air-core coil since this unit is meant as a prototype suitable for duplication by budding hams who might find it difficult to procure large-sized toroids. The two BC-type 330 pF air-variable tuning condensers were salvaged from old discarded radios. They were tested at 230 V AC to make sure that there was no arcing. If air-variable tuning condensers are not available, polyster-variable tuning condensers may be used, but the maximum RF power may have to be restricted to about 50 W.

The entire ATU-cum-Reflectometer is assembled on a bakelite sheet 6.25″ by 3.5″ that was available with me. Hams wishing to build this unit are advised to use a slightly broader sheet. The main coil is wound with 16-gauge copper wire on a short length of 1.25″ dia. plastic water-pipe tubing. The coil has 16 turns spaced to a length of 1.5″ with taps at 8 and 14 turns. The centre of the winding is the earth point. In the Norcal ATU, the RF output is taken through a 6-turn link winding, but in this unit, the messy link is dispensed with and the output is taken from a tap 6 turns from the earth point. Even with this simplification, the ATU works satisfactorily.
vu2 JN ATU
Fig.2. Photo of the ATU with Reflectometer

The open coil will produce a weak RF field in the shack. If the builder wishes so, the unit can be put in an aluminium box, but then (1) leave a minimum space of one diameter around the coil, (2) since the body of the tuning condensers is not at ground potential, leave a small gap between the shafts of the condensers and the front panel, and (3) use knobs with pointers for the tuning condensers (to indicate their position).

The toroids are 0.38 in. o.d. through which runs a short length of RG-174U coax. The centre conductor of the coax forms the primary of the winding, and the outer braid is used as a Faraday shield by grounding at one end only. The secondary windings of the toroidal pick-up coils consist of 18 turns of 24-gauge copper wire. The 1N34A rectifier circuit is used only on the reflected-power side. If the builder wishes so, this indicator can be easily upgraded to a full-fledged SWR bridge.

The visual indicator is a robust disposal-type 500 uA meter that was available in my junk-box. The resistor that comes in series with the meter should be not less than 5 K, and is selected so that there is a substantial reflected-power indication with a mismatched antenna. Since modern transceivers have built-in SWR protection circuitry, there is some sort of automatic control on the reflected power reading. Therefore no sensitivity control is needed.

With the transceiver and antenna connected to the unit, RF power is applied, and the two condensers are adjusted for zero reflected-power indication. Since no reduction drives are used, the condensers need to be tuned very carefully. A very slight hand-capacitance effect is present, but is not bothersome. The ATU-cum-Reflectometer is performing very well, and is able to tune my coax-fed 40-metre dipole on 80 metres, and bring down the reflected power to zero. To sum up, this is a simple and satisfying homebrew project.

PS: The photo reveals the need for some finishing touches on coil L1 that were initially postponed and then forgotten!

— VU2JN.

Note from VU2SWX : OM  Jayaraman has permitted me to  play with tis cute tuner . The unit is currently in my shack.

Categories: Computers Tags:

At barcamp kerala 7

December 23rd, 2009 6 comments

I took a session on recycling old PCs with LTSP at   barcamp kerala 7 last Sunday.  Even though I am associated  with the organizers of barcamp ever since its inception in Kerala, I could not attend any of the previous ones due to various reasons. So I was a bit skeptical about the kind of people I may meet. Also, this was the first public lecture I gave after assuming charges of Principal College of Engineering Attingal. I  conveniently hid this fact from the audience suspecting that my job profile might overshadow the geek in me.

ltsp
I was picked up from home by Kenney Jacob at 5.30 am  and we stated our journey to Changannasery on a TATA VISTA . The car was fantastic with GPS can other gizmos . A few of Kenney’s colleagues were also present in the car. We reached the  venue around 8.45 to find that the  gates of the Krishtu Jayanti college were closed. Kenny made some frantic telephone calls and finally we were asked to enter the college via  the  gates of a Catholic church.

There were around  70 guys in the hall. There was some initial hiccups and the  sessions took some time to start . I missed introductory remark by Kevin as I went to the nearest tea shop for a quick dose of coffee. The next session from Prassed Pai on 3d graphics programming was good and reminded me of my PG classes at CUSAT where we did all the shading and drawing algorithms. I think most of the audience was clue less about the topic.
The next session    Building Complex Website the Drupal Way from  Fredrik Jonsson? was   enlightening.
The third  session on Media by Kenney Jacob initiated some interesting discussions among the audience. Some of the participants expressed the fears about corporate media  manipulating facts .
Next was a cake cutting session . Some one suggested Fredrik Jonsson’s name for the event and every one clapped  when he cut the big cake sponsored by   ayruz web holdings  . Later I had lunch at a local teashop .
I took the first session in the after noon. My Idea was to set up my laptop as ltsp server and net book as the client . Then project the client to  the  big screen and start the presentation on the client.
The Sharp projector  at the venue was behaving erratically. It showed only half of the screen. I had to change instantly to the white board and start writing.  I briefly explained the  LTSP  with a figure that I drew and later on moved the projector to my laptop. The presentation was shown after explaining things with a white board.  I think half of the audience got confused by then.
The next session from UST global was  quite boring. I think such PR crap should be avoided in barcamps. I missed the session by Binny VA as I went out for a tea again.

The last session on linux devices was good,  but Praseed Pai  seemed to be the only person understanding it.
Finally, Fr. Abraham Mulamootil made a surprise appearance. I think it is the first time a catholic priest is seen publicly in a bar(camp). Any way he seems to be the only geek in the church.
The entire event was wound up around 6pm.
The facilities at the venue were pathetic.  No one from the college turned up. There was no net connectivity.  The wifi link of the college was running but their firewall was preventing outgoing net  request. Hope the next barcamp at Thiruvalla will be better and more interesting.

Categories: Computers, Gnu/Linux Tags:

BSNL GPRS on Ubuntu 9.10

December 1st, 2009 2 comments

As I travel frequently  in connection with my official and no-official engagement, my internet presence is disrupted. I have tons on mails and rss feed entries to be read after each journey. I was thinking of buying a netbook.
I recently bought a Toshiba NB200 netbook at a discount rate from my cousin. It came with 160 GB hard disk 1GB RAM, intel atom processor and Windows XP was pre-installed.
The first thing I did with the netbook was to remove windows. I installed ubuntu netbook remix 9.10, All the hardware except sound was instanly recognised by ubuntu. My next task was to  make it internet ready. I looked for various solutions like evdo from BSNL , netconnect from reliance etc. They all looked costly.
Finally I decided to go in for GPRS connection from BSNL. I  am already an unlucky owner of Nokia N72 , which is recognised only from windows. Fortunately the GPRS modem on N72 is accessible from linux . Here is what I did with my BSNL prepaid  phone connection to get it ready for my net book.

1) Enable GPRS on the phone

The GPRS can be enabled on BSNL connections by sending an SMS to  53733 with the following  word.  GPRSPRE. (I use a prepaid connection). They charge heavily    for GPRS usage 10 paise per KB.  However, they have some schemes which provide unlimited Internet access.
If you are a sporadic traveller, unlimited gprs access  for one day can be availed at Rs.20. For ardent travellers, an unlimited connection for one month can be subscribed at Rs 230. For availing the special schemes, you have to send sms to 53733 with the word GPRS20 (or GPRS230). You need a minimum balance of Rs 75 in your prepaid account for availing GPRS20. Once you send the sms,BSNL will ask you to confirm the scheme by sending another sms with GPRS20Y to 53733. (Sometimes it takes an hour or so  to get back the sms asking for confirmation. Being an Indian, you have to be patient.)

2) Configuring the Modem.

This was rather easy as my N72 GPRS modem was recognised as soon as I plugged the data cable.
I verified its presence  by looking at dmesg output on a terminal.

I installed wvdial from the ubuntu repository .

$ sudo apt-get install wvdial

Next, I ran the following command.

$ sudo wvdialconf

It created a minimal configuration file for wvdial  /etc/wvdial.conf.

/etc/wvdial.conf was then edited as shown below.

[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init3 = AT+CGDCONT=1,”IP”,”GPRSSOUTH.CELLONE.IN”,””,0,0
Modem Type = USB Modem
Modem = /dev/ttyACM0
Baud = 115200
Dial Command = ATD
Phone = *99***1#
Username =9194461xxxxx
Password =9194461xxxxx
New PPPD = yes
Stupid Mode =yes

Use your phone number as username and password. I entered the phone number including the country code as shown above. Also look at the Init3 entry. If you are in south India, you can use the above line. For other regions look at this page.

Now you can access internet by dialling out using wvdial.

$ sudo wvdial

The internet speed is reasonable.

I am posting this from Venad Express on my way back from Model Engineering college where I delivered a lecture  on free software. The netbook was really handy for the presentation too.

Categories: Computers, Uncategorized Tags:

Hacked by Bader2010

May 30th, 2009 1 comment

I  was away  from home for a week and returned back yesterday evening.  As I had a weeks emails pending, the first thing I did after reaching home was to  access gmail. To my horror,  google was telling me that I am providing a wrong password. Then, I tried to log in to my blog. I found out that my blog has been defaced. I was getting the following screens, Some Arabic bymn was played in the background.

bad1

bader2010

This page will give you some more information on how a hacked page look like.    I contacted my web hosting provider  and got the password for the site reset and the site was  back with in my control.

However  gmail id  was my lifeline and I had to recover it at any cost. I tried to  recover my password from the gmail login page as below.

google1

The next page had these options.google2

I selected my account has  been compromised  which gave me the following link.

google4

The account recovery page is here. Have a look at it.  Your scucess in retrieving the  account lies in accurate answers in this page. I filled out the following sections.

google51

google6

Fortunately, I remembered who invited me to gmail.( I  had a gmail account at a time when gmail invites were sold on ebay).   Also, I use filters and labels heavily for handling mail.   There was some fuzziness with dates , still I could approximate it.   I have a couple of blogs linked to the account and an orkut profile. I knew only the url of my blog on blogspot.  I  was very skeptical whether I will get it back. I submitted and waited  any response form google.  About an hour later I recievd the following mail from google.

google7

I reset the password and  retrived my account.  The attaker had tried to capture some of my other  on line assets from the gmail id. Some of  the automated responses had his IP address logged( or it might be a proxy). I traced the attacking  IP  to Saudi Arabia.

Why I lost my account ?

There  may be several reasons. Here are some of my assumptions .

a) I had a weak password. ( 6 letters and that too based on a dictionary word)

b) I had enabled POP3 access for my gmail account, even though I was not using it. There are plenty of scripts like this available on the Internet  for  brute force  attack on gmail accounts via POP3.

c) I had used my account from a friends place last week  on a windows XP machine. May be that machine has a key logger installed and the attacker might have obtained the password via IRC  from there.  I cheeked my home machines  for  any possible root kits,  but I could not find any.   My windows machines do not have internet access.

d) Some one might have stolen the password from one of the machines that I use at college. ( As we are having vacation now , I  can safely rule out this possibility)

What  information one must keep about  google accounts.

1) If some one invited to a gmail account ,  keep the email.  It can save you a lot of trouble.  It will give you some idea about the date of creation  of your account.

2)  If you use labeling and filters , remember the labels.  You can give easy to remember names  and  context relevant labels to your mail.

3)  Even if you are not blogging , create a blog on blogspot . The URL of the blog can be an important information.

4)  Email addresses are not by hearted as phone numbers.  So export the your gmail contact list to a file and keep it. The account recovery page asks for   up to five frequently contacted email ids. ( Click on contacts on the left side of any gmail page and select export to save the contacts.)

5) Set up a secondary email id  and give it a different password.  ( You can use Settings->Accounts->google account settings-change security question for this.)

6) Set up a  security question.  It can save you a lot of trouble.

7) If you use orkut, keep the URL of your orkut profile.

You can obtain it from your orkut home page as shown in the figure below.

orkut

9) Disable POP3 and IMAP if you are not using them.

10 Use a Strong password. This is the most important step.  In the change password page, make sure that your password is strong as shown in the picture  below.

gmialpass

Categories: Computers, Electronics Tags: