Sunday, September 8, 2013

Microprocessor Unit(MPU) & Micro-controller Unit(MCU)

1. What is the full form of 'MPU' & 'MCU'?
Ans: MPU: Microprocessor Unit; MCU: Micro-controller Unit.

2. What is the difference between MPU & MCU?
Micro Controller
Microprocessor is heart of Compute system.
Micro Controller is a heart of embedded system.
It is just a processor. Memory and I/O components have to be connected externally
Micro controller has external processor along with internal memory and i/O components
Since memory and I/O has to be connected externally, the circuit becomes large.
Since memory and I/O are present internally, the circuit is small.
Cost of the entire system increases
Cost of the entire system is low
Due to external components, the entire power consumption is high. Hence it is not suitable to used with devices running on stored power like batteries.
Since external components are low, total power consumption is less and can be used with devices running on stored power like batteries.
Most of the microprocessors do not have power saving features
Most of the micro controllers have power saving modes like idle mode and power saving mode. This helps to reduce power consumption even further.
Since memory and I/O components are all external, each instruction will need external operation, hence it is relatively slower.
Since components are internal, most of the operations are internal instruction, hence speed is fast.
Microprocessor have less number of registers, hence more operations are memory based
Micro controller have more number of registers, hence the programs are easier to write.
Microprocessors are based on von Neumann model/architecture where program and data are stored in same memory module
Micro controllers are based on Harvard architecture where program memory and Data memory are separate
Mainly used in personal computers
Used mainly in washing machine, MP3 players

Wednesday, April 24, 2013

Artificial Satellite

A satellite is any object or body that orbits around another object. An artificial satellite is any human made object designed to orbit the Earth or any other celestial body. The is no where near all about artificial satellites. There is a seemingly overwhelming amount of technology and engineering that goes into building even the simplest artificial satellite. Despite the challenges of constructing an artificial satellite, there are thousands of them orbiting our planet.

In 1957, the Soviet Union launched the world’s first satellite, known as Sputnik. Since then, dozens of countries have launched satellites, with more than 3,000 currently operating spacecraft going around the Earth. There are estimated to be more than 8,000 pieces of space junk; dead satellites or pieces of debris going around the Earth as well. Good news is that, Bangabandhu-1 will be Bangladesh's first satellite. This satellite will stay at 119.1° East longitude. (To know more Click Here)

Satellites can be classified by their functions. Satellites are launched into space to do a specific job. The type of satellite that is launched to monitor cloud patterns for a weather station will be different than a satellite launched to send television signals across Canada. The satellite must be designed specifically to fulfill its function.

Below are the names of ten different types of satellites with example-
  • Astronomy satellites - Hubble Space Telescope
  • Atmospheric Studies satellites - Polar
  • Communications satellites - Anik E
  • Navigation satellites - Navstar
  • Reconaissance satellites - Kennan, Big Bird, Lacrosse
  • Remote Sensing satellites - Radarsat
  • Search and Rescue satellites - Cospas-Sarsat
  • Space Exploration satellites - Galileo
  • Weather satellites - Meteosat
  • Military satellites- The U.S deafness.

Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a satellite as a relay station for their communication. One Earth Station sends a transmission to the satellite. This is called a Up-link. The satellite Transponder converts the signal and sends it down to the second earth station.  This is called a Down-link.

Working process of a satellite is very easy. A antenna, low noise amplifier (because the signal is initially very small), input filters to get rid of any noise from Earth, high power amplifiers to be able to send the signal back to earth, output filter to eliminate noise from satellite hardware and signals adding together, another antenna.

If some part of a satellite breaks down, but the satellite remains capable of doing useful work, the satellite owner usually will continue to operate it. In some cases, ground controllers can repair or reprogram the satellite. In rare instances, space shuttle crews have retrieved and repaired satellites in space. If the satellite can no longer perform usefully and cannot be repaired or reprogrammed, operators from the control center will send a signal to shut it off.

The advantages of satellite communication are
  • The coverage area of a satellite greatly exceeds that of a terrestrial system.
  • Transmission cost of a satellite is independent of the distance from the center of the coverage area.
  • Satellite to Satellite communication is very precise.
  • Higher Bandwidths are available for use.

The disadvantages of satellite communication
  • Launching satellites into orbit is costly.
  • Satellite bandwidth is gradually becoming used up.
  • There is a larger propagation delay in satellite communication than in terrestrial communication.



Tuesday, April 23, 2013

Internet Filtering


Internet filters are software tools that can help monitor web content viewed on a particular computer or network. In the case of family safety settings, Internet filters can also help parents manage who kids can communicate with or how long kids can use the computer. Internet filter is a software solution, commonly known as a content-filtering solution or web filtering solution that is designed and configured to make decisions on the type of the sites and content on those sites the users are allowed to visit. The content filtering device decides on what content should be made available to the user and what shouldn't be. The reason to have such a solution is basically to have a kind of internet censorship on the users using a particular system where the software is installed. Initially these kinds of solutions were normally used in home environments where the parents would like to have control on the content available to their children while they are browsing the Internet. Basically to keep the children away from pornography, violence, terrorism, etc.
Later on the internet filtering took on a whole new leap and was realized to have potential for corporate internet control and later on even country level internet control. Organization around the world saw the benefits of internet control as a way of limiting the sites that users can navigate to during their work hours. This served the dual purpose of preventing the employees from wasting their work time on entertainment and personal work and protection of the corporate network from the malicious content that the users might visit accidentally while browsing the web.
The internet filtering tool a whole new censorship meaning when countries across the world started adopting the filtering technology at the ISP level and at the internet perimeter of the country to block certain unwanted sites. A good example would be the blocking of pornographic sites in some countries where it is considered illegal to view such content.

Purpose of Filtering

For many years the Brethren have warned us of the dangers that accompany the Internet, and have counseled us to employ some technological barriers to the unending flow of filth that permeates the otherwise wonderful and extremely useful virtual world of the Internet. Recall President Hinckley’s warning in 2002, when he said: “Guard your homes. How foolish it seems to install bars and bolts and electronic devices against thieves and molesters while more insidious intruders stealthily enter and despoil”, or more recently when Elder Oaks told us in April conference, 2005: “We must also act to protect those we love. Parents install alarms to warn if their household is threatened by smoke or carbon monoxide. We should also install protections against spiritual threats, protections like filters on Internet connections.”

A common question that arises is whether Internet filters really work. The answer depends on what you are attempting to accomplish with the filter. If you are attempting to prevent accidental access to inappropriate content, then most filters can be considered successful.
Many filters also have other features, such as time controls, chat logging, reporting and other useful capabilities. All of these features help keep our family safe, and help provide us with more information regarding how our computers are being used. From this perspective, it would be safe to say that filters work.
One of the unfortunate side-effects of installing a filter is the false sense of security that it provides. Most teenagers can get around just about any filter if they really want to, and parents need to know how this is done so they can watch for the warning signs. Also be sure to use the tools that the filter provides, such as usage reports, blocked site reports, etc. A filter is not a silver bullet, and it is not a set-it-and-forget-it solution.
Increasing individual accountability is one of the most effective ways of filtering content. It is a good practice to place the computer in a public place, and to limit the use of the Internet to times that others are around. Windows Vista/7 and Mac OS X offer time limits on internet access, as do most filters. Many home routers now also offer availability schedules for protecting non-computer devices.
The only foolproof filter is, as President Faust once explained, the personal moral filter: "As the traffic on the communications highway becomes a parking lot, we must depend more and more on our own personal moral filters to separate the good from the bad." 

Types of filtering

There are various kinds of filtering techniques that are employed:

Host based filtering

Through this technique software is installed on the system by the administrator and rules are configured according to the needs of the administrator.
Now when the normal users try to browse internet and the browsing activity is in violence of the rules that have been set by the administrator, the content will be blocked and the user shall not be able to view it.

Server side filtering

 This methodology is normally adopted by companies and organizations at the gateway level. The company can install a hardware or a software that is capable filtering traffic at the gateway level and rules would be configured that will apply to all the users inside the company network.

Content Filtering at the ISP level

 Many internet service providers now days are providing such a service at some additional cost along with the internet link.
The companies and organization who do not wish to invest in their own gateway level content filtering device can go for this option and notify the ISP of their content filtering conditions. Based on those conditions, the ISP would filter the traffic at the ISP level itself.
Content filtering is also done at browser level as well, but this methodology is not as effective as the other three options. The reason is that users can change the browser settings and by pass the filtering that has been set through the browser.

Client-Side vs. Server-Side

Client-side filtering is installed directly onto the PC like any other software program. From there, it monitors Internet activity, blocking inappropriate content. Both home users and businesses can use client-side Internet filtering. Server-side filtering typically resides on the company server, controlling access for all connected computers. warns that server-side filtering isn't very customization  making a client-side solution more viable. While both may utilize the same blocking or filtering tactics, client-side software typically has more customization, a broader feature set and more frequent updates. 

Black & White List Filters

Blacklist filtering, according to, is one of the more popular methods, because of its ease of use. This type of software requires the parent or administrator to manually enter websites deemed inappropriate. After the website is recorded by the software, further access will be denied. White-list filters use the same principle, just in reverse. This much-stricter method requires the parent or administrator to specify websites that can be accessed instead of ones that can't. In other words, this method filters out the majority of the Internet, allowing access only to specifically pre-determined websites.

Keyword and Content Filters

Keyword and content filtering software takes a similar approach to black and white-list filters, only filtering out websites with specific words or pre-defined content. For example, a home Internet filter might offer to filter out pornographic content. The software will then try to determine, through the words used on the site and previously data-based information, whether a specific site is pornographic. If so, the user will be denied. According to, this method is often ineffective, because it tends to block legitimate websites misinterpreted as inappropriate. Conversely, if the keyword or content filter is set too low, it may allow unwanted content through, unable to recognize the site for what it is.

Types vs. Methods

While both client- and server-side Internet filtering are two different types, within those types there are methods that specify just how the software goes about filtering content. Understand the methods, such as blacklisting filters and keyword filters, is important to making an informed decision about what to buy. In other words, knowing whether a filter is client- or server-based isn't enough. You should also find out the method used and evaluate whether that's the right method for your family or company. 

Internet Filtering in different country

Internet Filtering in Australia

In Australia internet filtering has only recently been discussed as being implemented by the Australian Government (Foo, 2008). Whilst Australia at the time of writing does not have a national internet filtering policy, parents were able to filter the internet in their own homes using software subsidized by the Australian Government. Foo (2008) quotes Senator Conroy who stated, "With less than 150,000 filters accessed or downloaded and only 20 per cent of these still in use, the program has clearly failed.". This failure of parents to filter the internet in their homes is outside of the scope of this paper but the lack of uptake and continued usage shows that filtering of undesirable content is not being implemented on an individual level.
Filtering in the form that the Australian Government was considering is one of the first that can be considered a democratic decision of the people to implement filtering. (Bambauer, 2008) The Australian filtering program is unique due to it being part of an election campaign policy. Thus filtering can be implemented by law rather than using informal pressure on internet providers as in the United Kingdom. (ibid) Since obtaining government the scope of the filtering program has changed from unlawful material being filtered to also incorporating content that is considered unlawful. (ibid) It is the broadening of the scope that has drawn interest and raises concerns on what is considered filtering and when the filtering constitutes censorship.
Depken (2006) comes to a conclusion that,
"..those with kids, who are married, who are older, who use the internet for religious content, who work in the public sector, and who think pornography or privacy are the predominant issue concerning the Internet tend to favor Internet censorship."
Whilst this conclusion is true not all people fall into the categories mentioned thus demonstrating that not all people are in favor of censorship. Australia is one of the first Western countries to formally and legally implement internet filtering nationally, whilst claiming to protecting their citizens from inappropriate content. The writings have not been conclusive in determining if all filtering is censorship. The Australian model demonstrates the lack of distinction between filtering and possible crossing into censorship due to policy forming part of an election campaign in a democratic election without a clearly defined agenda. The issues of when a country protecting content crossing borders should be allowed but government but is a free manner with defined courses of request for access. In the case of Australia, the government does have the right to filter the internet but the way in which filtering is implemented must be carefully done with openness so it cannot be constituted as censorship.

Internet Filtering in the People's Republic of China

Internet censorship in the People's Republic of China is conducted under a wide variety of laws and administrative regulations. There are no specific laws or regulations which the censorship follows. In accordance with these laws, more than sixty Internet regulations have been made by the People's Republic of China (PRC) government, and censorship systems are vigorously implemented by provincial branches of state-owned ISP s, business companies, and organizations.
The censorship is not applied in Hong Kong and Macau, as they are special entities recognized by international treaty vested with independent judicial power and not subject to most laws of the PRC,including those requiring the restriction of free flow of information.
China started its Internet censorship with three regulations issued by China’s central government. The first regulation was called the Temporary Regulation for the Management of Computer Information Network International Connection. The regulation was passed in the 42nd Standing Convention of the State Council on 23 January 1996. It was formally announced on 1 February 1996, and updated again on the 20th of May 1997.
 The content of the first regulation states, “No units or individuals are allowed to establish direct international connection by themselves.” (Item 6) “All direct linkage with the Internet must go through China-net  GBNet, CERNET or CSTNET. A license is required for anyone to provide Internet access to users.” (Item 8) The second regulation was the Ordinance for Security Protection of Computer Information Systems. It was issued on February 18th of 1994 by the State Council to give the responsibility of Internet security protection to the Ministry of Public Security, which is entitled to “supervise, inspect and guide the security protection work”, and to “investigate and prosecute illegal criminal cases” (Item 17)
The Ordinance regulation further led to the Security Management Procedures in Internet Accessing issued by the Ministry of Public Security in December 1997. The regulation defines "harmful information" and further lists five kinds of harmful activities regarding Internet usage, “ (1) Intruding in a computer information network or making use of network resources without authorization; (2) Canceling, altering or adding functions in a computer information network without authorization; (3) Canceling, altering or adding data and application software for the purpose of memory, processing, or transmission in a computer information network without authorization; (4) Intentionally producing, disseminating destructive software such as a computer virus; (5) Other activities that are harmful to the security of a computer information network.” (Item 6)

Internet filtering in Bangladesh

An intelligence agency in a report submitted to the home ministry suggested that the government should monitor activities on social networking such as Facebook and Twitter round-the-clock 'so that any evil axis cannot hatch conspiracies by launching campaigns against the government on the sites.'
Evaluating the recent unrest in the Arab world and Middle East countries, the agency put forth a number of suggestions in the report 'Analysis of the impact of the political crisis in Arab world on social and political situation of Bangladesh.' The hoe ministry sent to report to other ministries on May 22.
The report analyzed the use of information technology in Egypt's upheaval which became popular as 'generation text' and it warned the government of such a situation and suggested the round-the-clock monitoring of Facebook and Twitter 'so that no evil axis can hatch conspiracies by campaigning against the government.'
The report also made some suggestions on local issues which could trigger public unrest such as managing traffic congestion by making roads off-limit to rickshaws and evicting hawkers from footpaths.
It also emphasized making warm the relations with Middle Eastern counties so that the market of Bangladeshi manpower remains stable.
Senior home ministry officials said the copies of the report had been sent to ministries of food, energy, expatriates' welfare and communications.
At a meeting of the cabinet committee on law and order on January 26, intelligence agencies also suggested that the government should monitor web contents. The suggestion was made after several incidents of violence in the Chittagong Hill Tracts. 
Earlier on May 30, 2010, Bangladesh blocked access to Facebook after satirical images of the Prophet Muhammad and the country's leaders were posted online.
The intelligence agency suggested that the government should mobilize public opinion against the opposition's possible attempt of evil politics centering on price spiral and the shortage of gas, power and water. The agency also called for creating a good relation with newspapers and the electronic media.
The report also stressed the need for a single spokesperson for the government to limit scopes for misinterpretation of the government's position.
In the wake of uprising in the Middle East, the agency called for ensuring energy security by exploring petroleum and modernizing energy production and distribution and by importing petroleum from countries outside the Middle East and OPEC members.
The report also suggested that the government should arrange employment of expatriate workers who were forced to return home for the turmoil in the Middle East and other countries.

How internet filters work

Internet Safety for Schools

Internet Filtering Product Guide Schools' and parents' concerns about safe surfing have created a market for products that allow Internet users to control the kind of content they receive on their computers. These various filtering solutions all deny access to a manually created and maintained list of Web sites, called a "not" list. These products rely on vendors' keeping up with the proliferation of "not" sites and adding them to their restricted list.
The major development that has changed schools' filtering requirements is the growth of sophisticated school network infrastructures, linking hundreds or thousands of computers. Any filter that has to be downloaded, installed, and configured on each computer on a large network is not a viable solution for schools with such a network

Parental Control

Internet due to its free nature contains information about each and every subject that you can name. This huge bulk of information contains some inappropriate or objectionable material like pornographic content, classified information and textual or visual material that can be provocative. Research had shown that most of the crimes in developed world are linked directly or indirectly to use of internet. Watching or reading objectionable material can be extremely harmful for the health and safety of your child and loved ones and it becomes your responsibility to save them from this destructive content.
Due to the distributed nature of internet it is very difficult to totally block a website both for individuals and governments. This is where parental control features help you. Parental control refers to special features that can be added to Mobile phones, computer software, televisions, video games and other electronic devices.
This basic purpose of parental control features on these devices is to limit access to certain information, surveillance and security reasons. Almost all the high tech internet security programs such as antivirus software have the parental control feature in them.
Like Norton is an antivirus product from Symantec Corporation, it had got one of the best and advanced parental control features. Similarly other antivirus software like bit defender and kaspersky internet security have parental control features in them. Along with that, Operating systems like Windows 7, Linux, Windows Vista and Mac OSX have parental control features in them.
There are several methods of implementing these features. For example to block a website on your computer you can add that website to the blocked list of your operating system or of antivirus software. Stand alone parental control programs are also available in market. These programs are powerful enough to block any kind of website from opening on your computer.
Parental control software can even block or monitor the API in order to scrutinize internet application like web browser or chatting software. You can also protect your confidential information by using parental control software. To protect sensitive information from being displayed on internet you can add specific keywords such as passwords and pin codes to your blocked database.
The parental control software will monitor the chat window and would intervene to block the flow of information upon finding a match in the banned database. Parental control software has self protection modules and have got passwords to stop unauthorized access. On the basis of their working we can classify parental controls in four categories.

Content Filters

Content filters are the most popular and basic kind of parental control. Content filters simply block access to a website depending on its content. Specific websites or content phrases are stored in database of filter and upon founding a matching entry the access is blocked. Content filters can block images and even media files. Content controls can also be applied on digital televisions to limit access to certain channels.

Usage Controls

Usage controls are more technical and sophisticated filters. They can be used in computers, televisions, automobiles and music players. You can turn your television or computer or internet off at certain time or control the volume of music player. Similarly you can control the speed of your child's car sitting miles away and know exactly where he or she is.

Computer Usage monitoring tools

Computer usage monitoring tools are specifically designed for computers. They are often incorporated inside an internet security suite or an antivirus program. Stand alone versions of computer monitoring programs are also available. Such features are also available in operating systems such as windows seven, windows vista and Mac OSX. These programs are used to block websites and protect privacy and prevent leakage of confidential information.


Surveillance programs have the same capabilities as spyware. Their basic purpose is to keep record of all the activities being performed on a machine. Surveillance programs are stand alone software that can be installed on any machine. For that you have to be the legal owner of the machine or parents have the authority to monitor their kids activities, if they are aged below 18 then covertly and above that age by their consent.
Examples of surveillance programs are key loggers and monitoring tools. This software is designed to operate in stealth mode. They keep recording all the activities that are being performed on a machine and make a log file of them. This log file can be later viewed by the administrator or even can be e-mailed on his Id.
Most of the antivirus and internet security programs consider key loggers and monitoring bots as spyware, you must be legally eligible to install such software on a machine. 


Either way we go, there is always going to be a downfall to censoring the Internet. If we let the government do it for us, we will not only be letting them take our first amendment rights, but also our fourth amendment rights because the internet does not stop at web pages. You will let the government see your e-mail, and go into your computer, and see what you are looking at. If they can take away our fourth amendment rights on the internet, which is to say they won't start pulling over every car, and seeing what is inside. The alternative, filtering programs are not efficient, and block too much information. The ideal way to prevent children from pornography, and not get rid of all of the information on the Internet would be the new system they are trying to organize called Platform Internet Content Selection. What this system will do is make a rating system for web pages, very similar to that of the T.V. each person in your house hold will have a user id, and based on what the administrator specifies on what ratings you can see, you will be able to see certain web sites. The only drawback is who decides what material is objectionable, but this will always be a problem. Censoring the Internet would be taking a huge step back. The Internet is full of ideas, and things we can benefit from and we should censor it.

  1. Overpowering the Goliath in Our Lives, President Gordon B. Hinckley, Ensign, January 2002
  2. 2. Pornography, Elder Dallin H. Oaks, Ensign, May 2005
  3. 3. The Power of Self-Mastery, President James E. Faust, Ensign, May 2000
  4. (21 July 2011)
  5. (21 July 2011)
  6. (21 July 2011)
  7. (3 August 2011)
  8. (1 August 2011)


Monday, February 25, 2013

Power Plant

 Solar power Plant

Hydro Power Plant

Nuclear Power Plant

 Thermal Power Plant

 Wind Power Plant


Sunday, February 24, 2013

kVA=kVAR+kw, wind generator and solar panel, Simple DC motor, ac servo motor construction


 wind generator and solar panel

 Simple DC motor

ac servo motor construction

Lie Ditector

Essential Materials

         সার্কিট বোর্ড/Circuit Board
         ক্যাপাসিটর/Capacitor - C1:1μF
         রেসিস্টর/Resistor- R1-1.5kΩ, R3: 1.5kΩ
         ভেরিয়েবল রেসিস্টর/Veriable resistor- (R2: 5-10kΩ))
         ট্রান্সিস্টর/Transistor- (Q1: 2N3565)
         এনালগ মিটার /Analog meter- (M1: 0-1 mA)
          টা পেন্সিল ব্যাটারি(6 pencil battery  (1.5*3. & 1.5*3 = .)
          টি ইলেকট্রোড /  টি ক্লিপ(2 electrode/2 clip )

প্রথমেইযাকে পরিক্ষা করবেনতার হাতে ইলেকট্রোড / ক্লিপ দুটি লাগিয়ে দিন। লক্ষ রাখবেনআপনার এই দুটি ইলেকট্রোড / ক্লিপ কিন্তু আপনার সার্কিটের ইনপুট হিসেবে কাজ করবে। তাই চামড়ার সাথে এই দুটি ইলেকট্রোড / ক্লিপ যেন ভাল ভাবে সংসুক্ত থাকে। এবারসার্কিটে দেখানো R2 (ভেরিয়েবল রেসিস্টর)টি কে বাড়িয়ে অথবা কমিয়ে আপনার এনালগ মিটারের মান টিকে  শুন্যে নিয়ে আসুন। আপনার সার্কিটের প্রস্তুতি শেষ
এখন আপনি আপনার প্রশ্ন করুন। যাদি দেখেনআপনার এনালগ মিটার এর কাটা নেগেটিভের দিকে যাচ্ছেতবে যাকে আপনি প্রশ্ন করছেনতিনি মিথ্যা বলছেন
ব্যাস হয়ে গেল আপনসাধারন মিথ্যা কথা ধরার যন্ত্র

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