SANTOSH BAN: BLOG

फागुन २३ र २४ गते नेपाल बन्द

2013-03-06T21:01:00.000+05:45

२०६९ फाल्गुन २३ गते संघिय गणतान्त्रिक परिषदले आम हड्तालको घोसणा गरेको छ ल्

समय : बिहान सबेरै देखि बेलुका ५:०० बजे सम्म

2069 March 6 Wednesday. फाल्गुन २३ - General Strike

2069 March 7 Thursday. फाल्गुन २४ - Nepal Bandha

***copied from another site... if you are owner and it is copyright protected, ,mail me at susanme19@gmail.com ,i will remove it.

How Nepal Telecom WiMax can increase internet user in Nepal

2013-02-26T00:03:00.000+05:45

WiMAX is the fourth generation of communication system which consists very high speed internet service at low cost. Nepal telecom (NT) is preparing to introduce WiMAX technology for the first time in Nepal. According to the spokesperson of Nepal Telecom, “Telecom is very near to start WiMAX technology in Nepal”. Customers of Kathmandu valley can experience WiMAX before the Dashain festival. The fifteen BTS towers are already been set up by Nepal telecom. “The final test will be done between the Dashain and Tihar festival and will be soon started professionally” said the spokesperson.

How WiMAX is different than current WIFI system in Nepal

We have two options now: Wifi or WiMAX? Certainly, they both are initially designed for different purposes. Wifi tends to provide Internet service within closed area to the WiFi access point whereas WiMAX is more powerful and broad version of WiFi which provides Internet Service to the broad area. Here are the key differences:

a) Coverage:

Wifi and WiMAX coverage differences are best understood comparing them with Cordless phone and mobile phones. Wifi, like a cordless phone works without wire but in a limited small area which means less coverage. WiMAX, on the other hand being mobile phone provides connection to a significantly greater distance. Wifi supports transmission ranges up to a few hundred meters whereas WiMAX could support range up to 30 miles.

b) Quality of Service:

WiMAX also has some benefits over Wifi in terms of connection quality. Users are actually battling for connection whereas in wimax each user gets a constant allotment of broadband access. Broadlink and Wordlink operates wifi network which might be resulting in the above problem. Users can experience varying levels of broadband width resulting in the fluctuation of speed whereas user will have quality constant bandwidth thus the constant and quality service with NTC Wimax.

c) Speed:

Comparing the speed of Broadlink and Worldlink WiFi’s and NTC WiMAX certainly the WiMAX users will experience better and constant speed. Like mentioned earlier there will be a huge fluctuation in the speed of WiFi whereas each individual user will get the constant bandwidth in WiMAX resulting the constant and fastest Internet service compared to WiFi.

Nepal Telecom plan on WiMAX

Telecom aims to provide WiMAX internet connection to all of the village development committees (V.D.C), municipalities and major cities of Nepal within one year. This project cost is about 10 million dollars. The agreement between Nepal Telecom and US-based equipment manufacturer and network solution provider company Airspan collaborates to introduce WiMAX for the first time in Nepal. To use WiMAX you must have an CPE device. In the current Nepali market, three types of CPE are available. If you are in the range of one kilometer of the main tower then you can use the indoor CPE. If you are in the range of 2 to 4 kilometer then you have to install the low range outdoor CPE and if you are more than 4 kilometer range of the main BTS then you have to install the high range outdoor CPE to use the WiMAX internet service. NTC has already launch some big plan including installation of Google cache server, and increasing bandwidth for existing adsl user.

Costumers will get minimum speed of 256kbps, which is treated as broadband speed in Nepal. Telecom is establishing Core Network in Kathmandu and setting up 200 BTS towers in eastern Nepal and at the same time, establishing Core Network in Butwal for the Western Region which helps people of rural area to access internet easily. It was never been such easy for rural internet connection before. NTC claimed that WIMAX will be volume based. User can’t get unlimited service like exiting ADSL or WIFI service provide by existing various ISP.

Does WIMAX hampers other ISP of Nepal

Most of the other Internet service provider rely on WiFi technology. Most of the existing service provider like Broadlink, Worldlink use different device for WiFi connectivity to end user from BTS. Due to the various factor like Geographical location of country, the architectural of the building, noise between BTS, it is almost impossible to provide the perfect WiFi connection to the end user. Despite of good customer support of private ISP, many end user are not fully satisfied. WiMAX can help to fill those gaps. But the question lies on the customer support of NTC. Nepal telecom is never good at providing customer service. Their service are pathetic which may bound user to switch to WiMAX from their current WiFi connection. the user who is using WiFi also need to buy extra device for WiMAX. Unless people see strong benefit they don’t prefer to spend extra money to get new connection. NTC comes with pathetic volume base plan which is not useful for heavy internet user.

Final conclusion: WiMAX is a perfect option for the country like Nepal where fiber connection can’t be made accessible to every VDC. NTC must be revere for this decision. NTC doesn’t have a good history of providing good customer support. Thus, many people still raised the question about WiMAX. If NTC would able provide good service and support to the user and there would be involved of private ISP for providing WiMAX services, there would be huge development in Tele communication system of Nepal.

Content is copied from another site. If any one of you is the owner of this content, inform me, i will remove it. **Sources**

The 7 Layers of the OSI Model

2013-02-25T10:33:00.000+05:45

The OSI, or Open System Interconnection, model defines a networking framework to implement protocols in seven layers. This article explains the 7 Layers of the OSI Model.

The OSI, or Open System Interconnection, model defines a networking framework to implement protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Application (Layer 7)

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Presentation (Layer 6)

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Session (Layer 5)

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Transport (Layer 4)

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Network (Layer 3)

This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

Data Link (Layer 2)

At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Physical (Layer 1)

This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

***Content is copied from anothe site. If any one of you is the owner of this content, inform me, i will remove it.

WiMAX Wireless Network

2013-02-24T19:28:00.001+05:45

In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.

WiMAX system consists of two parts:

A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km).

A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.

A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas.

What this points out is that WiMAX actually can provide two forms of wireless service:

There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions -- they are better able to diffract, or bend, around obstacles.

There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth.

WiFi-style access will be limited to a 4-to-6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter's 30-mile radius (2,800 square miles or 9,300 square km of coverage). This is what allows WiMAX to achieve its maximum range.

The final step in the area network scale is the global area network (GAN). The proposal for GAN is IEEE 802.20. A true GAN would work a lot like today's cell phone networks, with users able to travel across the country and still have access to the network the whole time. This network would have enough bandwidth to offer Internet access comparable to cable modem service, but it would be accessible to mobile, always-connected devices like laptops or next-generation cell phones.

how you access the Internet today

2013-02-24T19:16:00.000+05:45

Broadband access

In your home, you have either a DSL or cable modem. At the office, your company may be using a T1 or a T3 line.

WiFi access

In your home, you may have set up a WiFi router that lets you surf the Web while you lounge with your laptop. On the road, you can find WiFi hot spots in restaurants, hotels, coffee shops and libraries.

Dial-up access
If you are still using dial-up, chances are that either broadband access is not available, or you think that broadband access is too expensive.
The main problems with broadband access are that it is pretty expensive and it doesn't reach all areas. The main problem with WiFi access is that hot spots are very small, so coverage is sparse. What if there were a new technology that solved all of these problems? This new technology would provide:
The high speed of broadband service Wireless rather than wired access, so it would be a lot less expensive than cable or DSL and much easier to extend to suburban and rural areas.

Broad coverage like the cell phone network instead of small WiFi hotspots.

This system is actually coming into being right now, and it is called WiMAX. WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.

WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. In the same way that many people have given up their "land lines" in favor of cell phones, WiMAX could replace cable and DSL services, providing universal Internet access just about anywhere you go. WiMAX will also be as painless as WiFi -- turning your computer on will automatically connect you to the closest available WiMAX antenna.

My Website's Home Page: under Construction

2012-12-12T01:01:00.000+05:45

Home Page Screecshoot

Windows 7 / Windows 8 Apache error–Port 80 is unable to start

2012-12-05T17:03:00.000+05:45

This is one of the most popular problems in windows 7/8. There are several common situations, and remedies.(my problem has been solved by using step ***)

Situation #1: Because of Skype

If you have skupe installed, you need disable the following option to fix it.

Situation #2: Internet Information Services (IIS)

You are running IIS Server. There are two possible solutions. One is to turn off IIS server by opening IIS Server Manager, the other is to completely disable IIS server service in your computer.

Situation #3: Port 80 used by unknown process

First of all, open cmd. You can do so by opening Run and then typing cmd, then pressing enter.After opening cmd, type this

netstat -aon

It will give some output. Find out the line something like this. It will contain something that will look like :80.

Notice the PID (Process ID)? Now, open task manager by pressing Ctrl+Shift+Esc. Go to the process details and look for the PID you found out. In this case, its PID is 4.

Now, this is a weird situation. As you can see, it is a system process. You should not close a system process. Moreover, it’s description NT Kernel & System, meaning it is being used to run the process which is using port 80 and we don’t actually know which process is using it.

However, this is also solvable. After a bit of digging, I found that it is also a common scenario(!) to have NT Kernet & System grab port 80 for one particular service in both Windows 7 and Windows 8.

Go to Run prompt again. Type services.msc and press enter. It will show the services. Find the service by the name Web Deployment Agent Service. You have to stop it (by right clicking, or by the left menu). And after stopping you should be able to run Apache in port 80 without any problem.

What if Web Deployment Agent Service is not running?

Well – I am not sure what to do if it is a system process, and grabbed port 80, and is not Web Deployment Agent Service.

I found the Process ID and it is not Skype, or IIS, or System!

Cool. Shut it down through task manager. (After you are sure that you have saved all things related to it and it is not an important process)

*** I do not want to stop the process which grabbed port 80. But I still want to run Apache!

Great!!You will have to change the port of Apache then. You can change it by opening this file.

Then find this line

1\|	ApacheDirectory/conf/httpd.conf
2\|	Listen 80

See that 80? That’s the port. Change it to another value, for example 8080. You will be able to start Apache after that. Remember to access it through browser using port. For example, if the address you want to access is localhost of Apache running in port 8080, you have to enter localhost:8080 in browser.

Fujitsu Lifebook 2013 – A Truly "All-In-One" Concept Device

2012-11-28T18:58:00.001+05:45

The Fujitsu Lifebook 2013 Concept unites a laptop, tablet, phone and camera together in one device. Even if we've seen devices that come close, this concept takes the cake when it comes to multi-functionality.

The ASUS Padfone may be able to transform itself from a phone to a tablet, but the Fujitsu Lifebook 2013 takes that idea a few steps further.

Where a keyboard would be, the laptop holds a small tablet. As soon as the tablet is in the slot, the tablet itself becomes a full size touch-based QWERTY Keyboard.

While this may seem a bit silly, imagine if the tablet could just as easily transform itself into a sketchpad or a second screen for gameplay. I could imagine that being quite useful. It is also helpful for syncing the contents of your phone with your laptop effortlessly and without any wires.

The KT Spider Concept is a laptop we first saw at IFA this year which syncs your phone with your laptop with a similar slot, but it doesn't replace the keyboard. The Fujitsu Lifebook 2013 concept goes much farther, and also includes a slot for a smartphone on the outer case of the laptop.

I think the pouch for the phone looks awkward, and I'm not sure folks would prefer typing on a tablet screen in lieu of an actual physical keyboard, but I can see how this could be helpful for sketching things or for certain kinds of gameplay. I also think that as more and more folks begin using their smartphones as cameras, the need for a device devoted purely to taking photos lessens. But who am I to judge an imaginary device? This is an interesting concept, nonetheless, especially for multi-screen gameplay!

Mobile Bands: Dual-Band/Tri-Band/Quad-Band

2012-11-24T12:52:00.000+05:45

Dual-Band

also known as dual-band or dualband. A dual-band phone operates at both the 900 MHz and 1800 MHz spectrum. Dual-band works in Europe, Africa, Asia, Australia, New Zealand and much of South America.

In Europe two bands (900/1800 MHz) are used in the same country to improve coverage.

In America two bands (850/1900 MHz) are used in the same country to improve coverage.

Dual band phones are also used to enable roaming between different countries. For example, a cellphone with dual band 850/1800 MHz will work in both the United States (850 MHz) and India (1800 MHz).

Tri-Band

also known as tri-band or triband. A tri-band phone operates on three frequency bands, 900 MHz, 1800 MHz and 1900 MHz, allowing you to use it in Europe, Africa, Asia, nearly all of North America, Australia and New Zealand

2G Triband phones are mobile phones that support the GSM 900/1800/1900 MHz bands commonly sold in Europe, Asia and Africa, (for example the LG KE820 is a triband mobile phone that is sold in Europe, but works in big cities of America but not so well in suburbs and rural areas).Or alternatively the 850/1800/1900 bands (commonly sold in the Americas). The Motorola V300 formerly carried by Rogers Wireless used a rare combination of 850/900/1900. A 2G Quad band (850/900/1800/1900) offers more coverage and is now quite common.

A 3G Quad band offers more coverage.

Quad-Band

also known as quad-band or quadband. A quad-band phone allows you to roam almost anywhere globally. It covers the 850 Mhz, 900 MHz, 1800 MHz and 1900 MHz frequency ranges. Many countries in South America only have 850 MHz GSM service while both 1900 MHZ and 850 MHz GSM services are supported in the USA. 99% of all countries use the GSM standard. We believe eventually GSM will be the only cell phone standard in the world.

A quad-band mobile phone is used to designate a phone that can operate in the following GSM frequency bands:

850 MHz (U.S./Canada/Latin America/Brazil (Only the carrier Vivo))
900 MHz (Africa/Europe/Brazil/Africa/Australia/Asia (ex Japan and S. Korea))
1800 MHz (Africa/Europe/Australia/Asia/Brazil)
1900 MHz (U.S./Canada/Latin America)

VLC Media Player Magic...!!!

2012-11-19T20:54:00.000+05:45

As the name of the post suggest this a trick using VLC Media Player.

See the image below After reading this post you can also be able to do this as this very simple...!!!

STEP TO DO THIS:-

Open VLC Media Player
Press Ctrl+N
After this you will see an window will appear as shown below

There type screen://
And the click the play button below.
Then you will see magic happening in your VLC Media player window,Every thing will move backward endlessly...!!!!

Try this And Enjoy...!!! Like Share & give your Feedback if this Trick works...!!!

How to Download Torrent Files Using IDM

2012-11-19T20:35:00.000+05:45

IDM(Internet Download Manager) is the best and fastest download manager.It downloads files at high speeds compared to other download managers.Internet download manager speed doesn't depend on seeders,leeches etc,it only depends on your Internet connection.Downloading Torrent Files With IDM is really useful when you are downloading files with less seeds.

Now lets know the steps how to make this possible....!!!

You can download torrent files using IDM by just following the simple steps...!!!

Go to zbigz.com

Signup for a free account there. After the signup process is finished go to your torrent's search engine and search for the file which you want to download.

Now go to zbigz.com and then hit on upload and choose the torrent file which you have downloaded previously then hit GO.

After you hit go your torrent file will be downloaded by high speed and your file will be ready to download.

Again, When you hit download button then a box will pop up asking the type of download you want either free or premium.Then Just choose Free and Enjoy...!!!

This all about how you can download a torrent file using IDM.

Try this and sahre this with your friends...!!! Comment below your feedback and also contact if you face any problem...!!!

How to post blank status update on facebook

2012-11-19T19:47:00.000+05:45

Hello everyone, here is simple trick to post blank status update on facebook. This is simple and easy.

Just click on update status and enter the following code and Click Post.

The Code is:

@[2:2: ]

Bouncing Ball Animation

2012-11-18T20:36:00.000+05:45

This is a simple animation showing bouncing ball. It is animated by using well known best animating software Autodesk Maya.The basic theme of this animation is creating suitable number of picture frame by frame and playing them with specific time (frame/sec). Larger the number of frame gives best quality of animated video.

Windows 8 Professional (x86|x64)

2012-11-17T19:33:00.000+05:45

Microsoft Windows 8 Professional (X86|X64) Final Retail AIO

Microsoft Windows 8 Professional Final Retail AIO - To be honest I was a bit confused about the final version of Windows 8, is there a more recent version of Windows 8 Final Retail or not. But if the view of news Operating System Windows 8 are scattered on the internet , Retail Final version is the latest. Well,, been a few days since many friends softmenia are requesting Windows 8 Final AIO, so in this article is to present the softmenia AIO version. For those who are interested to have the OS Windows 8 Retail Final, let's let's please directly secured before destroyed the file.

Screenshot

**HERE IS Microsft Windows 8 Professional Final Retail English x86/x64 Version, After activation No Watermark included and the proof is below.

Download Link

1 GB / Part via BillionUpload

Microsoft Windows 8 Professional (x86/x64) Final Retail AIO - (3.83GB)

Link password: -abank.doank-

250 MB / Part via Hulkshare

Microsoft Windows 8 Professional (x86/x64) Final Retail AIO - (3.83GB)

Rar password: koskomputer.blogspot.com

Instruction

Unpack

Mount ISO

Install the Windows

Use loader to active

Enjoy

* If you download from Hulkshare, rename parts extension after downloaded complete.

Example: Name_file.rar.mp3 to Name_file.rar

Torrent Link is here(Better you download from torrent link)

Windows 8 Pro (MSDN)

Some Snaps

2012-11-17T14:51:00.001+05:45

Download Internet Download Manager - (Latest)

2012-05-10T19:10:00.000+05:45

Download Internet Download Manager with crack and instruction-(Latest)

Internet Download Manager v6.12.10.3 With crack and serial numberClick Here For Download.

Click Here for Download

Steps to Install Internet Download Manager

Extract the folder to you Hard Disk
Install idman608.exe
Exit the program. (Right click on the green icon of IDM found in the system tray –> Exit)
Copy the file “IDMan” from the folder crack, in install folder, by default: C:\Program Files\Internet Download Manager and confirm to overwrite existing file.
Run the file “regkey” from folder “crack” to register the program.

** If after install you get the message “Fake serial number…”, run “Unregister.IDM.reg” to remove any previous serial from registry, then use “RegKey Windows 32-bit or 64-bit” to activate IDM. If you still have problems, uninstall IDM, run “Unregister.IDM.reg”, reboot PC, install IDM again, use the crack & regfile to activate it. That´s all.

Note: If you get any message to that new update is available, DO NOT TRY TO UPDATE. You can come back to this page and you’ll get links for the new version of IDM.

How WebCam works

2012-05-09T20:30:00.000+05:45

Webcam is a device used to capture images, audio and videos. Webcam are either inbuilt or can be externally attached with computer. The most common application of a webcam is video chat, video recording, image capturing. A webcam generally consist of a lens, an image and sound sensors, electronic circuitry to process the data and send it to PC.

A variety of webcams with different features are available in the markets. Depending on the features and quality, the technologies used and the prices vary. However the basic function remains the same. You can see an optical lens to capture the images/videos and a small hole to capture sound. The bottom part of the body consists of a plastic casing which provides support to the webcam and a mechanism to fix the webcam on the top of the laptop.

Little tips about building your own RC helicopter

2012-04-29T18:25:00.000+05:45

Flying RC helicopter is really very exhilarating. Their versatility gives a RC pilot a complete access to the three-dimensional space in such a way that no other machines can! I have played RC helicopter for more than one year but still find that I have just learnt a few tricks that it can perform.

For More Click Here

2012-04-27T22:24:00.000+05:45

WINDOWS COMMAND

Accessibility Options : access.cpl
Add Hardware : hdwwiz.cpl
Add / Remove Programs : appwiz.cpl
Administrative Tools : control admintools
Automatic Updates : wuaucpl.cpl
Wizard file transfer Bluethooth : fsquirt
Calculator : calc
Certificate Manager : certmgr.msc
Character : charmap
Checking disk : chkdsk
Manager of the album (clipboard) : clipbrd
Command Prompt : cmd
Service components (DCOM) : dcomcnfg
Computer Management : compmgmt.msc
DDE active sharing : ddeshare
Device Manager : devmgmt.msc
DirectX Control Panel (if installed) : directx.cpl
DirectX Diagnostic Utility : dxdiag
Disk Cleanup : cleanmgr
System Information : dxdiag
Disk Defragmenter : dfrg.msc
Disk Management : diskmgmt.msc
Partition manager : diskpart
Display Properties : control desktop
Properties of the display (2) : desk.cpl
Properties display (tab "appearance") : control color
Dr. Watson : drwtsn32
Manager vérirficateur drivers : check
Event Viewer : Eventvwr.msc
Verification of signatures of files : sigverif
Findfast (if present) : findfast.cpl
Folder Options : control folders
Fonts (fonts) : control fonts
Fonts folder windows : fonts
Free Cell : freecell
Game Controllers : Joy.cpl
Group Policy (XP Pro) : gpedit.msc
Hearts (card game) : mshearts
IExpress (file generator. Cab) : IExpress
Indexing Service (if not disabled) : ciadv.msc
Internet Properties : inetcpl.cpl
IPConfig (display configuration) : ipconfig / all
IPConfig (displays the contents of the DNS cache) : ipconfig / displaydns
IPConfig (erases the contents of the DNS cache) : ipconfig / flushdns
IPConfig (IP configuration cancels maps) : ipconfig / release
IPConfig (renew IP configuration maps) : ipconfig / renew
Java Control Panel (if present) : jpicpl32.cpl
Java Control Panel (if present) : javaws
Keyboard Properties : control keyboard
Local Security Settings : secpol.msc
Local Users and Groups : lusrmgr.msc
Logout : logoff
Microsoft Chat : winchat
Minesweeper (game) : winmine
Properties of the mouse : control mouse
Properties of the mouse (2) : main.cpl
Network Connections : control NetConnect
Network Connections (2) : ncpa.cpl
Network configuration wizard : netsetup.cpl
Notepad : notepad
NView Desktop Manager (if installed) : nvtuicpl.cpl
Manager links : packager
Data Source Administrator ODBC : odbccp32.cpl
Screen Keyboard : OSK
AC3 Filter (if installed) : ac3filter.cpl
Password manager (if present) : Password.cpl
Monitor performance : perfmon.msc
Monitor performance (2) : perfmon
Dialing Properties (phone) : telephon.cpl
Power Options : powercfg.cpl
Printers and Faxes : control printers
Private Character Editor : eudcedit
Quicktime (if installed) : QuickTime.cpl
Regional and Language Options : intl.cpl
Editor of the registry : regedit
Remote desktop connection : mstsc
Removable Storage : ntmsmgr.msc
requests the operator to removable storage : ntmsoprq.msc
RSoP (traduction. ..) (XP Pro) : rsop.msc
Scanners and Cameras : sticpl.cpl
Scheduled Tasks : control schedtasks
Security Center : wscui.cpl
Console management services : services.msc
shared folders : fsmgmt.msc
Turn off windows : shutdown
Sounds and Audio Devices : mmsys.cpl
Spider (card game) : spider
Client Network Utility SQL server : cliconfg
System Configuration Editor : sysedit
System Configuration Utility : msconfig
System File Checker (SFC =) (Scan Now) : sfc / scannow
SFC (Scan next startup) : sfc / scanonce
SFC (Scan each démarraget) : sfc / scanboot
SFC (back to default settings) : sfc / revert
SFC (purge cache files) : sfc / purgecache
SFC (define size CAHC x) : sfc / cachesize = x
System Properties : sysdm.cpl
Task Manager : taskmgr
Telnet client : telnet
User Accounts : nusrmgr.cpl
Utility Manager (Magnifier, etc) : utilman
Windows firewall (XP SP2) : firewall.cpl
Microsoft Magnifier : magnify
Windows Management Infrastructure : wmimgmt.msc
Protection of the accounts database : syskey
Windows update : wupdmgr
Introducing Windows XP (if not erased) : tourstart
Wordpad : write
Date and Time Properties : timedate.cpl
Accessibility Options : access.cpl
Add Hardware : hdwwiz.cpl
Add / Remove Programs : appwiz.cpl
Administrative Tools : control admintools
Automatic Updates : wuaucpl.cpl
Wizard file transfer Bluethooth : fsquirt
Calculator : calc
Certificate Manager : certmgr.msc
Character : charmap
Checking disk : chkdsk
Manager of the album (clipboard) : clipbrd
Command Prompt : cmd
Service components (DCOM) : dcomcnfg
Computer Management : compmgmt.msc
DDE active sharing : ddeshare
Device Manager : devmgmt.msc
DirectX Control Panel (if installed) : directx.cpl
DirectX Diagnostic Utility : dxdiag
Disk Cleanup : cleanmgr
System Information : dxdiag
Disk Defragmenter : dfrg.msc
Disk Management : diskmgmt.msc
Partition manager : diskpart
Display Properties : control desktop
Properties of the display (2) : desk.cpl
Properties display (tab "appearance") : control color
Dr. Watson : drwtsn32
Manager vérirficateur drivers : check
Event Viewer : Eventvwr.msc
Verification of signatures of files : sigverif
Findfast (if present) : findfast.cpl
Folder Options : control folders
Fonts (fonts) : control fonts
Fonts folder windows : fonts
Free Cell : freecell
Game Controllers : Joy.cpl
Group Policy (XP Pro) : gpedit.msc
Hearts (card game) : mshearts
IExpress (file generator. Cab) : IExpress
Indexing Service (if not disabled) : ciadv.msc
Internet Properties : inetcpl.cpl
IPConfig (display configuration) : ipconfig / all
IPConfig (displays the contents of the DNS cache) : ipconfig / displaydns
IPConfig (erases the contents of the DNS cache) : ipconfig / flushdns
IPConfig (IP configuration cancels maps) : ipconfig / release
IPConfig (renew IP configuration maps) : ipconfig / renew
Java Control Panel (if present) : jpicpl32.cpl
Java Control Panel (if present) : javaws
Keyboard Properties : control keyboard
Local Security Settings : secpol.msc
Local Users and Groups : lusrmgr.msc
Logout : logoff
Microsoft Chat : winchat
Minesweeper (game) : winmine
Properties of the mouse : control mouse
Properties of the mouse (2) : main.cpl
Network Connections : control NetConnect
Network Connections (2) : ncpa.cpl
Network configuration wizard : netsetup.cpl
Notepad : notepad
NView Desktop Manager (if installed) : nvtuicpl.cpl
Manager links : packager
Data Source Administrator ODBC : odbccp32.cpl
Screen Keyboard : OSK
AC3 Filter (if installed) : ac3filter.cpl
Password manager (if present) : Password.cpl
Monitor performance : perfmon.msc
Monitor performance (2) : perfmon
Dialing Properties (phone) : telephon.cpl
Power Options : powercfg.cpl
Printers and Faxes : control printers
Private Character Editor : eudcedit
Quicktime (if installed) : QuickTime.cpl
Regional and Language Options : intl.cpl
Editor of the registry : regedit
Remote desktop connection : mstsc
Removable Storage : ntmsmgr.msc
requests the operator to removable storage : ntmsoprq.msc
RSoP (traduction. ..) (XP Pro) : rsop.msc
Scanners and Cameras : sticpl.cpl
Scheduled Tasks : control schedtasks
Security Center : wscui.cpl
Console management services : services.msc
shared folders : fsmgmt.msc
Turn off windows : shutdown
Sounds and Audio Devices : mmsys.cpl
Spider (card game) : spider
Client Network Utility SQL server : cliconfg
System Configuration Editor : sysedit
System Configuration Utility : msconfig
System File Checker (SFC =) (Scan Now) : sfc / scannow
SFC (Scan next startup) : sfc / scanonce
SFC (Scan each démarraget) : sfc / scanboot
SFC (back to default settings) : sfc / revert
SFC (purge cache files) : sfc / purgecache
SFC (define size CAHC x) : sfc / cachesize = x
System Properties : sysdm.cpl
Task Manager : taskmgr
Telnet client : telnet
User Accounts : nusrmgr.cpl
Utility Manager (Magnifier, etc) : utilman
Windows firewall (XP SP2) : firewall.cpl
Microsoft Magnifier : magnify
Windows Management Infrastructure : wmimgmt.msc
Protection of the accounts database : syskey
Windows update : wupdmgr
Introducing Windows XP (if not erased) : tourstart
Wordpad : write
Date and Time Properties : timedate.cpl

2012-04-27T22:07:00.000+05:45

How GPS Works

Our GPS System was actually invented by the U.S. Army for military purposes (eg missile guidance, tracking planes and soldiers, or navigation) Later, they made the system available to civilians.

The system consists of three parts

24 - 32 Satelittes (only twelve are visible at once) in orbit around the Earth.
Ground stations for monitoring and controlling the satelittes.
A GPS receiver that calculates the position.

The twenty-four satelittes are in a certain orbit around our planet. They continously broadcast a signal down to Earth including the current time and the orbit information. The math and equations for determining a precise position is extremely complex, but the general concept is simple.
It takes four satelittes to determine your position. Each of those satelittes transmits a time signal. By comparing the time sent from the satelitte to the GPS Receiver's own clock, the elapsed time of the transmission can be determined. Because the position of the satelitte is known and because we know how fast the message travels through space, the distance between the receiver and the satelitte can be determined. The receiver then repeats this with the other three satelittes and triangulates a position.

GPS Modules

Crunching down all those time signals and calculating a coordinate requires a massive amount of processing power (at least for a small handheld receiver) The best thing to do is buy a module that does all the work for you!

The EM-406A (pictured above) is a fantastic module! It costs about $60 from SparkFun Electronics. They have tons of other great modules too, like the Locosys LS20031 or the EM408. To make it easy to interface to a PC or a microcontroller, these modules have a TX / RX Serial Port that is usually at 4800 bps. Some modules even let you change this.

QuadCopters – How to get started

2012-04-27T19:24:00.001+05:45

In this blog post I will try to describe the different steps I have been thru to plan, design and build the prototype of my QuadCopter. There will be coming some more blog posts later on describing how to get the QuadCopter running, programming it, tuning it etc.

This blog post is divided into 3 parts

What is a QuadCopter
Brushless motors
Propellers
Roll, Pitch and Yaw
ESC – Electronic Speed Controller
Battery
The frame
Frame configuration
Inertial Measurement Unit
Controller electronics
Initial decisions
Theoretical calculator
Conclusion

What is a QuadCopter

In short terms a QuadCopter is what the name says a “copter”-like device with four rotors (quad). You might have seen one in action before, as they are being commercialized for police and monitoring use. You can also find them as toys, fx the AR Drone or even universities have been playing with them, developing swarms with them.

A swarm of nano copterClick Here For Video

QuadCopters can be found and built in many different sizes. All from the tiny ones that isn’t much larger than a CD ROM and up to QuadCopters with a motor-to-motor length of more than a meter.

To plan and build a QuadCopter there is a lot of terms you need to understand. So before planning my design I searched the internet for good resources for DIY QuadCopter and found the following links to be the best:

To give you a better understanding of what a QuadCopter contains I will now go thru some of the parts it contains.

As I said QuadCopters do have 4 motors with a propeller each. Most of the times the so called Brushless Motors are used to drive the propellers. Brushless motors are a bit similar to normal DC motors in the way that coils and magnets are used to drive the shaft. Though the brushless motors do not have a brush on the shaft which takes care of switching the power direction in the coils, and this is why they are called brushless. Instead the brushless motors have three coils on the inner (center) of the motor, which is fixed to the mounting. On the outer side it contains a number of magnets mounted to a cylinder that is attached to the rotating shaft. So the coils are fixed which means wires can go directly to them and therefor there is no need for a brush.

The reason why QuadCopters use brushless motors instead of normal DC motors is the much higher speeds and less power usage for the same speed. The brushless motors are more efficient as there is no power lost as there is in the brush-transition on the DC motors.

On this diagram of the brushed motor you will see that it is the coil that is rotating instead of the magnets as on the brushless. Brushless motors come in many different varieties, where the size and the current consumption differ. When selecting your brushless motor you should take care of the weight, the size, which kind of propeller you are going to use, so everything matches up with the current consumption. When looking for the brushless motors you should notice the specifications, especially the so called “Kv-rating”. The Kv-rating is an indication on how many RPMs the motor will do if provided with x-number of volts. The RPMs can be calculated in this way: RPM=Kv*U

Propellers

On each of the brushless motors there are mounted a propeller. You might not have noticed this on the pictures, but the 4 propellers are actually not identical. If you have a look at the CrazyFlie picture above you will notice that the front and the back propellers are tilted to the right, while the left and right propellers are tilted to the left.

This reason for this is that the motor torque of and the law of physics will make the QuadCopter spin around itself if all the propellers were rotating the same way, without any chance of stabilizing it. By making the propeller pairs spin in each direction, but also having opposite tilting, all of them will provide lifting thrust without spinning in the same direction. This makes it possible for the QuadCopter to stabilize the yaw rotation, which is the rotation around itself. The propellers come in different diameters and pitches (tilting). You would have to decide which one to use according to your frame size, and when that decision is made you should chose your motors according to that. Some of the standard propeller sizes used for QuadCopters are: EPP1045 – 10” diameter and 4.5” pitch – this is the most popular one, good for mid-sized quads APC 1047 – 10” diameter and 4.7” pitch – much similar to the one above EPP0845 – 8” diameter and 4.5” pitch – regularly used in smaller quads EPP1245 – 12” diameter and 4.5” pitch – used for larger quads which requires lot of thrust EPP0938 – 9” diameter and 3.8” pitch – used in smaller quads In general you should select your propeller according to the following four tips: The diameter of the propeller indicates how much air the propeller will be able to “move” while the pitch indicates how much air the propeller moves all the time – not said that you can use this in any way to calculate the air moved. The larger diameter and pitch the more thru the propeller can provide. But be-aware that a large pitch makes it much harder for the motor to drive it, it requires much more power, but in the end it will be able to lift more weight. When using high RPM motors you should go for the smaller or mid-sized propellers When using low RPM motors you should go for the larger propellers as you can run into troubles with the small ones not being able to lift the quad at low speed (RPM) A faster rotating propeller (small diameter and small pitch) is used when you have a motor that runs at a high RPM (Kv > 1000) and can provide a decent amount of torque. A slower rotating propeller (longer or larger pitch) is used when you have a motor that manages fewer revolutions but can provide more torque.

Roll, Pitch and Yaw

For this matter let’s just sum up what Roll, Pitch and Yaw is, as we are going to use these terms much more. Roll, Pitch and Yaw is some well used terms from the aircraft terminology. The terms are used to describe the objects orientation around each of its axis. Have a look at the picture below and I think you will understand the terms.

ESC – Electronic Speed Controller

As the brushless motors are multi-phased, normally 3 phases, you can’t just apply power to it to make it spin. The motors requires some special phase-control electronics that is capable of generating three high frequency signals with different but controllable phases, but the electronics should also be able to source a lot of current as the motors can be very “power-hungry”.

In this case we got the Electronic Speed Controllers, known as ESC’s. The ESCs is simply a brushless motor controller board with battery input and a three phase output for the motors. For the control it is usually just a simple PPM signal (similar to PWM) that ranges from 1ms (min speed=turn off) to 2ms (max speed) in pulse width. The frequency of the signals does also vary a lot from controller to controller, but for a QuadCopter it is recommended to get a controller that supports at least 200Hz or even better 300Hz PPM signal, as it should be possible to change the motor speeds very quickly to adjust the QuadCopter to the stable position. It is also possible to get ESCs that is controlled thru OneWire of I2C. These tends to be much more expensive though, but sometimes it is also possible to “mod” other ESCs to add the I2C feature.

ESCs can be found in many different variants, where the source current is the most important factor. You should always chose an ESC with about 10A or more in sourcing current as what your motor will require.

Another important factor is its’ programming facilities, as some ESCs support range programming while others do not. This means that with some ESCs you don’t necessarily have to use the “1ms to 2ms” range, but you can adjust it to your own needs – this is especially useful when we are going to make our own controller board.

Battery

All this leads to the battery, the power source for the whole device. For the battery two types can be used, whereof one of them is highly recommended. The NiMH and the LiPo. I won’t say much about the NiMH as most communities tells us to stay away from these for driving QuadCopters as they first and foremost are not able to provide enough current and secondly they weight a lot more than LiPo batteries when they have the necessary current ratings. Instead we should talk about LiPo batteries, but in this world there are also a lot of different variants of these too. LiPo batteries can be found in packs of everything from a single cell (3.7V) to over 10 cells (37V). The cells are usually connected in series, making the voltage higher but giving the same amount of amp-hours. For a QuadCopter you should go after the 3SP1 batteries which means 3 cells connected in series as 1 parallel (just forget the parallel, as it has no sense because we just use 3 cells in series). This should give us 11.1V but at fully charged it actually gives us around 12V instead. For a brushless motor with a Kv-rating of 1000, this gives us a maximum of 12000 rounds per minute. This number is totally fictive as the battery voltage will drop immediately to around 11.1V (at fully charged state) when current is being drained. Anyways, this gives us a good idea about how fast the propellers will be spinning!

As for the battery capacity regards you should make some calculations on how much power your motors will draw and then decide how long flight time you want and how much influence the battery weight should have on the total weight. A good rule of thumb is that you with four EPP1045 propellers and four Kv=1000 rated motor will get the number of minutes of full throttle flight time as the same number of amp-hours in your battery capacity. This means that if you have a 4000mAh battery, you will get around 4 minutes of full throttle flight time – though with a 1KG total weight you will get around 16 minutes of hover.
Another thing to be-aware of when selecting the right battery is the discharge rate, formerly known as the C-value. The C-value together with the battery capacity indicates how much current you are able to source from the battery. The calculations follow this simple rule: MaxSource = DischargeRate x Capacity
Take the Zippy4000 from the image above, which has a discharge rate of 20C and a capacity of 4000mAh. With this battery you will be able to source a maximum of 20Cx4000mAh = 80A. So in this case you should make sure that the total amount of current drawn by your motors (ESCs) won’t exceed 80A.
To make some more detailed calculations about your specific design I recommend you to visit the free xcopterCalc – Calculator for Multicopters. I will tell more about this in the “Initial decisions” section.

The frame

Every part in a QuadCopter design works together and the frame is the one joining all of them. The frame can be designed in many ways with many different kinds of materials. The important things are to make it rigid and to minimize the vibrations coming from the motors.

A QuadCopter frame consists of two to three parts which don’t necessarily have to be of the same material:

The center part where the electronics and sensors are mounted
Four arms mounted to the center part
Four motor brackets connecting the motors to the arms

Carbon Fiber
Aluminium
Plywood or MDF

Carbon fiber is the most rigid and vibration absorbant of the three materials but is also by far the most expensive.

Most of the times the arms used in QuadCopters are made of hollow aluminium square rails which makes the QuadCopter relatively light weight but still makes it rigid. The problem with these hollow aluminium rails are the vibrations, as they aren’t damped and will therefor vibrate to the center part and maybe mess up the sensor readings.

Instead solid MDF plates could be cut out for the arms as they will absorb the vibrations much better than the aluminium. Unfortunately we have another problem then, as the MDF plates are not very rigid and will break if the QuadCopter falls to the ground.
As for the center part everything from carbon fiber, aluminium or plywood can be used. Plywood is commonly seen as the center part because it is light weight, easy to work with and is reliable and rigid so it can hold the four arms together as required.
The arm length varies a lot from QuadCopter to QuadCopter as it is up to the individual to decide how big he would like his quad to be. In the QuadCopter terminology we use the abbreviation “motor-to-motor distance” to explain the distance for the center of one motor to the center of another motor of the same arm (or in the same direction).

The motor to motor distance decision goes hand in hand with the propeller diameter decision, as you should definitely make enough space between the propellers. Usual QuadCopters with EPP1045 propellers, which means a propeller diameter of 10”, has a motor to motor distance of around 60 cm ~ 24”, though it will be possible to make it less. Others with smaller propellers, fx with a diameter of 8” or less, will be able to have a motor to motor distance of around 12”.

Frame configuration

While the + configuration looks like this:

The difference is how the motors have to be controlled. For the + configuration the motor controlling is fairly simple as you just have one motor assigned to each direction. The negative aspect of the + configuration though is that you only have a single motor to provide extra thrust (speed up) when you want to move to another direction. In the X configuration you will always have two motors working together on changing direction.

IMU – Inertial Measurement Unit

Wow, I think this post is getting really big, and I haven’t even talked about the fun part yet – the IMU.
The Inertial Measurement Unit is the sensor system of the QuadCopter. The main purpose of the Inertial Measurement Unit is to calculate the orientation of the quad – the three orientation angles, Roll, Pitch and Yaw. These angles are then fed into some controlling electronics that uses those angles to calculate the required changes in the motor speeds.
The IMU consists of at least 6 sensors, also known as 6DOF. These sensors should be a 3-axis accelerometer and a 3-axis gyroscope. Sometimes another sensor, a 3-axis magnetometer, is added for better Yaw stability.

The accelerometers measures acceleration as the name indicates. Now you would think, “Why the heck do we need to measure acceleration to know the orientation?”, but yet again there is another law of physics – the gravity. The gravity is actually a downwards acceleration towards the center of earth, which to all objects makes a downward force keeping the objects on the surface. The accelerometer is actually measuring force, so the downwards gravity acceleration will also be measured by the accelerometer.
As the accelerometer sensor can measure the acceleration in three directions we can actually calculate how the accelerometer is oriented against the surface.

Fx when the accelerometer is held as the image above, the X axis will show positive 1g, while all the other two axis will show 0g.
Now the next question rises, “Why isn’t the accelerometer then enough to measure the orientation?”. The problem lies in the way the accelerometer works, because it isn’t very stable. If only the accelerometer were used to calculate the orientation even the smallest movements of the accelerometer will mess up the orientation. So if mounted on a QuadCopter with vibrating motors it will be no good.
Instead we use a gyroscope to address this problem. A gyroscope measure angular velocity, in other words the rotational speed around the three axis. The output of a gyroscope is given in radians per second or degrees per second. With both the accelerometer and gyroscope readings we are now able to distinguish between movement/vibration going up, down, left or right or rotation of the sensor, which is what we would like to know.
Final question, “Then why didn’t we just use the gyroscope when it can tell us the rotational movement?”. Yet again the problem lies in how the sensor works. The gyroscope tends to drift a lot, which means that if you start rotating the sensor, the gyroscope will output the angular velocity, but when you stop it doesn’t necessarily go back to 0 deg/s. If you then just used the gyroscope readings you will get an orientation that continues to move slowly (drifts) even when you stopped rotating the sensor.
This is why both sensors has to be used together to calculate a good and useful orientation.
For the Yaw rotational movement the accelerometer can’t be used as the reference sensor as it could with the Roll and Pitch movement. Instead a magnetometer is sometimes used. A 3-axis magnetometer measures the magnetic field that affects the sensor in all three directions. As the earth contains a magnetic field on the North- and South Pole, the magnetic sensor can be used to determine where north and south is located. The locations of these poles can then be used as a reference together with the angular velocity around Yaw from the gyroscope, to calculate a stable Yaw angle.
I won’t go more into details on how these calculations are done in this post. I will write another post soon with more details on these algorithms.
The 3 different sensors usually come in QFN or BGA packages which make it hard to do your own development with them. Instead people usually buy an IMU sensor board with 6DOF or 9DOF or even buy a complete IMU unit with processor and sensors.
Here is a list of some of the commercial available IMU sensors boards and units.

IMU sensor boards:

IMU units:

The raw sensor boards I’ve seen in use works either digitally by I2C or by analog. I prefer to use the digital boards as I2C is so easy and fast. Though if you got a fast processor with some good analog inputs capable of sampling fast enough, the analog boards seems to be more inexpensive than the digital ones.
The difference between the IMU sensors boards and the IMU units is that the IMU units contain a microprocessor. Usually it’s a small 8-bit microprocessor which will do the calculation of Pitch, Roll and Yaw by the use of some kind of algorithm. The calculated data will then be put out on a serial bus or sometimes also available by I2C or SPI.
The choice of IMU is going to reflect which kind of controller board you are going to use. So before rushing out buying one of these boards you should read the next section about the controller boards, as some of them do already contain the different sensors.

Controlling electronics

QuadCopters can be programmed and controlled in many different ways but the most common ones are by RC transmitter in either Rate (acrobatic) or Stable mode. You can either buy an already commercial available controller board or build one yourself. Someone is also doing a mixup by buying some of the parts, like an Arduino and the sensors but then they make the shield and some of the software themselves.
Here is a list of some of the commercial available controller boards that I have met on my way thru the QuadCopter jungle.

Some of the controller boards already contain the required sensors while other requires you to buy these on a separate board.

The AeroQuad board is fx a shield for the Arduino, either the Arduino UNO or the Arduino MEGA. The AeroQuad board requires the Sparkfun 9DOF stick which is soldered to the shield.
The ArduPilot board contains an ATMEGA328, the same as on the Arduino UNO. Like the AeroQuad shield this board doesn’t contain any sensors either. You would have to buy fx the ArduIMU and connect it to the board to use it.
The OpenPilot is a more advanced board which contains a 72MHz ARM Cortex-M3 processor, the STM32. The board also includes a 3-axis accelerometer and 3-axis gyroscope. Together with the board comes a great piece of software for the PC to calibrate, tune and especially set waypoints for your QuadCopter if you have installed a GPS module – which I will be talking more about in the next section.

As I said earlier QuadCopters are usually controlled in either Rate (acrobatic) or Stable mode. The difference is the way the controller board interprets the orientational feedback together with your RC transmitter joysticks.
In Rate mode only the Gyroscope values are used to control the QuadCopter. The joysticks on your RC transmitter are then used to set the desired rotation rate of the 3 different axes. In this mode you can control your QuadCopters speed of rotation around the 3 axis, though if you release the joysticks it doesn’t automatically re-balance. This is useful when doing acrobatics with your QuadCopter as you can tilt it a bit to the right, release your joysticks, and then your QuadCopter will keep that set position.
For the beginner the Rate mode is a bit hard to start with so instead you should start with the Stable mode. In the Stable mode all the sensors are used to determine the QuadCopters orientation in the air. This orientation is then used to calculate the speed of the 4 rotors to keep the QuadCopter balanced, being plan with the surface. The joysticks on your RC transmitter are then used to set the desired angle for the different axes. So if you would like to move your QuadCopter forward a bit you should simply tilt one of the joysticks so the desired Pitch angle will be changed. When releasing the joysticks the angle will be reset and the QuadCopter will be stable again.

Source

Kernel

2012-02-16T22:15:00.000+05:45

What is Kernel?

Kernel is the very essential central core part of the operating system which has complete control over everything that happen in the system. it provides basic service to all part of the operating system. It acts as a bridge between the Application and data processing at the Hardware level.It loads the data to the memory and runs after the BIOSGenerally it is stored to the protected memory space, which prevents it from being overwritten from other.

Generally it includes,

1) A Scheduler:It determines how the various processes share the processing time of the Kernel

2) A Supervisor:It gives use of the computer to each process when it is scheduled.

3) An Interrupt Handler;It handles all the interrupt requested from all the hardware devices.

4) A Memory Manager:It allocates memory.

Types of Kernel

There are four popular categories or kinds of Kernels namely monolithic kernels, microkernels, hybrid kernels and exokernels.

1)Monolithic Kernel:Monolithis Kernels are the part of Unix like operating system like Linux,FreeBSD etc. These types of kernel consists of the core part of the operating system and device driver with the ability to load the modules at the run-time.

2)Micro kernel:Microkernel are the part of the operating system like BeOS, Mac OS X, MINIX, QNX etc. These types of kernel generally provide only the minimal service such as defining memory address space, Inter-Process Communication (IPC) and memory management. Running the hardware process are not handled directly by Microkernel.

3)Hybrid Kernel:Hybrid Kernel it the part of the operating system like Microsoft Windows NT, 2000,XP etc. These types of kernel are the extension of the microkernel with some properties of monolithic kernel. These types of kernel are unable to load module during the run time.

4)Exokernel:Exokernel are evolving and still on experiment. It can corporate with multiple operating system library, that means it can handle more than one operating system at a same time, like we can use both windows and linux operating system at same time.

Digital SIganal Processing

2012-02-16T20:14:00.000+05:45

Architecture of the Digital Signal Processor

Digital signal processing (DSP) is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing. DSP includes subfields like: audio and speech signal processing, sonar and radar signal processing, sensor array processing, spectral estimation, statistical signal processing, digital image processing, signal processing for communications, control of systems, biomedical signal processing, seismic data processing, etc.

The goal of DSP is usually to measure, filter and/or compress continuous real-world analog signals. The first step is usually to convert the signal from an analog to a digital form, by sampling and then digitizing it using an analog-to-digital converter (ADC), which turns the analog signal into a stream of numbers. However, often, the required output signal is another analog output signal, which requires a digital-to-analog converter (DAC). Even if this process is more complex than analog processing and has a discrete value range, the application of computational power to digital signal processing allows for many advantages over analog processing in many applications, such as error detection and correction in transmission as well as data compression.[1]

DSP algorithms have long been run on standard computers, on specialized processors called digital signal processor on purpose-built hardware such as application-specific integrated circuit (ASICs). Today there are additional technologies used for digital signal processing including more powerful general purpose microprocessors, field-programmable gate arrays (FPGAs), digital signal controllers (mostly for industrial apps such as motor control), and stream processors, among others.

One of the biggest bottlenecks in executing DSP algorithms is transferring information to and from memory. This includes data, such as samples from the input signal and the filter coefficients, as well as program instructions, the binary codes that go into the program sequencer. For example, suppose we need to multiply two numbers that reside somewhere in memory. To do this, we must fetch three binary values from memory, the numbers to be multiplied, plus the program instruction describing what to do.

Figure 28-4a shows how this seemingly simple task is done in a traditional microprocessor. This is often called a Von Neumann architecture, after the brilliant American mathematician John Von Neumann (1903-1957). Von Neumann guided the mathematics of many important discoveries of the early twentieth century. His many achievements include: developing the concept of a stored program computer, formalizing the mathematics of quantum mechanics, and work on the atomic bomb. If it was new and exciting, Von Neumann was there!

As shown in (a), a Von Neumann architecture contains a single memory and a single bus for transferring data into and out of the central processing unit (CPU). Multiplying two numbers requires at least three clock cycles, one to transfer each of the three numbers over the bus from the memory to the CPU. We don't count the time to transfer the result back to memory, because we assume that it remains in the CPU for additional manipulation (such as the sum of products in an FIR filter). The Von Neumann design is quite satisfactory when you are content to execute all of the required tasks in serial. In fact, most computers today are of the Von Neumann design. We only need other architectures when very fast processing is required, and we are willing to pay the price of increased complexity.

This leads us to the Harvard architecture, shown in (b). This is named for the work done at Harvard University in the 1940s under the leadership of Howard Aiken (1900-1973). As shown in this illustration, Aiken insisted on separate memories for data and program instructions, with separate buses for each. Since the buses operate independently, program instructions and data can be fetched at the same time, improving the speed over the single bus design. Most present day DSPs use this dual bus architecture.

Figure (c) illustrates the next level of sophistication, the Super Harvard Architecture. This term was coined by Analog Devices to describe the internal operation of their ADSP-2106x and new ADSP-211xx families of Digital Signal Processors. These are called SHARC® DSPs, a contraction of the longer term, Super Harvard ARChitecture. The idea is to build upon the Harvard architecture by adding features to improve the throughput. While the SHARC DSPs are optimized in dozens of ways, two areas are important enough to be included in Fig. 28-4c: an instruction cache, and an I/O controller.

First, let's look at how the instruction cache improves the performance of the Harvard architecture. A handicap of the basic Harvard design is that the data memory bus is busier than the program memory bus. When two numbers are multiplied, two binary values (the numbers) must be passed over the data memory bus, while only one binary value (the program instruction) is passed over the program memory bus. To improve upon this situation, we start by relocating part of the "data" to program memory. For instance, we might place the filter coefficients in program memory, while keeping the input signal in data memory. (This relocated data is called "secondary data" in the illustration). At first glance, this doesn't seem to help the situation; now we must transfer one value over the data memory bus (the input signal sample), but two values over the program memory bus (the program instruction and the coefficient). In fact, if we were executing random instructions, this situation would be no better at all.

However, DSP algorithms generally spend most of their execution time in loops, such as instructions 6-12 of Table 28-1. This means that the same set of program instructions will continually pass from program memory to the CPU. The Super Harvard architecture takes advantage of this situation by including an instruction cache in the CPU. This is a small memory that contains about 32 of the most recent program instructions. The first time through a loop, the program instructions must be passed over the program memory bus. This results in slower operation because of the conflict with the coefficients that must also be fetched along this path. However, on additional executions of the loop, the program instructions can be pulled from the instruction cache. This means that all of the memory to CPU information transfers can be accomplished in a single cycle: the sample from the input signal comes over the data memory bus, the coefficient comes over the program memory bus, and the program instruction comes from the instruction cache. In the jargon of the field, this efficient transfer of data is called a high memory-access bandwidth.

Figure 28-5 presents a more detailed view of the SHARC architecture, showing the I/O controller connected to data memory. This is how the signals enter and exit the system. For instance, the SHARC DSPs provides both serial and parallel communications ports. These are extremely high speed connections. For example, at a 40 MHz clock speed, there are two serial ports that operate at 40 Mbits/second each, while six parallel ports each provide a 40 Mbytes/second data transfer. When all six parallel ports are used together, the data transfer rate is an incredible 240 Mbytes/second.

This is fast enough to transfer the entire text of this book in only 2 milliseconds! Just as important, dedicated hardware allows these data streams to be transferred directly into memory (Direct Memory Access, or DMA), without having to pass through the CPU's registers. In other words, tasks 1 & 14 on our list happen independently and simultaneously with the other tasks; no cycles are stolen from the CPU. The main buses (program memory bus and data memory bus) are also accessible from outside the chip, providing an additional interface to off-chip memory and peripherals. This allows the SHARC DSPs to use a four Gigaword (16 Gbyte) memory, accessible at 40 Mwords/second (160 Mbytes/second), for 32 bit data. Wow!

This type of high speed I/O is a key characteristic of DSPs. The overriding goal is to move the data in, perform the math, and move the data out before the next sample is available. Everything else is secondary. Some DSPs have on-board analog-to-digital and digital-to-analog converters, a feature called mixed signal. However, all DSPs can interface with external converters through serial or parallel ports.

Now let's look inside the CPU. At the top of the diagram are two blocks labeled Data Address Generator (DAG), one for each of the two memories. These control the addresses sent to the program and data memories, specifying where the information is to be read from or written to. In simpler microprocessors this task is handled as an inherent part of the program sequencer, and is quite transparent to the programmer. However, DSPs are designed to operate with circular buffers, and benefit from the extra hardware to manage them efficiently. This avoids needing to use precious CPU clock cycles to keep track of how the data are stored. For instance, in the SHARC DSPs, each of the two DAGs can control eight circular buffers. This means that each DAG holds 32 variables (4 per buffer), plus the required logic.

Why so many circular buffers? Some DSP algorithms are best carried out in stages. For instance, IIR filters are more stable if implemented as a cascade of biquads (a stage containing two poles and up to two zeros). Multiple stages require multiple circular buffers for the fastest operation. The DAGs in the SHARC DSPs are also designed to efficiently carry out the Fast Fourier transform. In this mode, the DAGs are configured to generate bit-reversed addresses into the circular buffers, a necessary part of the FFT algorithm. In addition, an abundance of circular buffers greatly simplifies DSP code generation- both for the human programmer as well as high-level language compilers, such as C.

The data register section of the CPU is used in the same way as in traditional microprocessors. In the ADSP-2106x SHARC DSPs, there are 16 general purpose registers of 40 bits each. These can hold intermediate calculations, prepare data for the math processor, serve as a buffer for data transfer, hold flags for program control, and so on. If needed, these registers can also be used to control loops and counters; however, the SHARC DSPs have extra hardware registers to carry out many of these functions.

The math processing is broken into three sections, a multiplier, an arithmetic logic unit (ALU), and a barrel shifter. The multiplier takes the values from two registers, multiplies them, and places the result into another register. The ALU performs addition, subtraction, absolute value, logical operations (AND, OR, XOR, NOT), conversion between fixed and floating point formats, and similar functions. Elementary binary operations are carried out by the barrel shifter, such as shifting, rotating, extracting and depositing segments, and so on. A powerful feature of the SHARC family is that the multiplier and the ALU can be accessed in parallel. In a single clock cycle, data from registers 0-7 can be passed to the multiplier, data from registers 8-15 can be passed to the ALU, and the two results returned to any of the 16 registers.

There are also many important features of the SHARC family architecture that aren't shown in this simplified illustration. For instance, an 80 bit accumulator is built into the multiplier to reduce the round-off error associated with multiple fixed-point math operations. Another interesting

feature is the use of shadow registers for all the CPU's key registers. These are duplicate registers that can be switched with their counterparts in a single clock cycle. They are used for fast context switching, the ability to handle interrupts quickly. When an interrupt occurs in traditional microprocessors, all the internal data must be saved before the interrupt can be handled. This usually involves pushing all of the occupied registers onto the stack, one at a time. In comparison, an interrupt in the SHARC family is handled by moving the internal data into the shadow registers in a single clock cycle. When the interrupt routine is completed, the registers are just as quickly restored. This feature allows step 4 on our list (managing the sample-ready interrupt) to be handled very quickly and efficiently.

Now we come to the critical performance of the architecture, how many of the operations within the loop (steps 6-12 of Table 28-1) can be carried out at the same time. Because of its highly parallel nature, the SHARC DSP can simultaneously carry out all of these tasks. Specifically, within a single clock cycle, it can perform a multiply (step 11), an addition (step 12), two data moves (steps 7 and 9), update two circular buffer pointers (steps 8 and 10), and control the loop (step 6). There will be extra clock cycles associated with beginning and ending the loop (steps 3, 4, 5 and 13, plus moving initial values into place); however, these tasks are also handled very efficiently. If the loop is executed more than a few times, this overhead will be negligible. As an example, suppose you write an efficient FIR filter program using 100 coefficients. You can expect it to require about 105 to 110 clock cycles per sample to execute (i.e., 100 coefficient loops plus overhead). This is very impressive; a traditional microprocessor requires many thousands of clock cycles for this algorithm.

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