circuitzone123

Some useful questions while facing an interview

2008-12-02T11:44:00.002+05:30

Introduction
Okay, so you have managed to hold your nerves in control and brave the questions of the HR. You are now at the end of your interview session. What next? The answer is, there are a few more steps to go. For instance, the HR person may ask you if you have anything to ask of him/her. How do you respond to that? It is quite likely that you are stressed out and nothing comes to your mind. This article deals with this situation and gives you a few intelligent questions that you may ask.
The Rationale
First of all let us try to understand why the HR person puts you in such a situation. Is he/she simply being nice to you or is there more to it? One possible reason is that the company wants to project an image of transparency. The company wants you to know that it encourages two-way communication between the top management and the subordinates, an atmosphere where everyone can ask relevant questions and expect to get answers. In other words, the company respects the employee’s need to know about matters that affect him, no matter where he is in the hierarchy.
Next, and more important, this situation checks your presence of mind and ability to form intelligent questions. So far you have been simply answering questions asked of you. How do you behave when you are in a position to ask questions? What kind of questions do you ask? It also shows how serious you are about the company and the job.
Let us get on to some questions now.
Some Useful Questions
Before you set out to ask questions, keep the above reasons in mind. It would be good to sincerely thank the HR person for such an opportunity. You can start with something like “I have really enjoyed this opportunity to meet you and your team at .. (the company name). Yes, there are a few things I would like to know, thank you for asking” However it is not wise to ask the HR a volley of questions and turn it into a counter interview. Consider the questions below and choose one or two from them that you find the most useful to you.

What do you personally find the most enjoyable part of working for this company?
May I ask why or how you joined this organization? / What brought you here?
I would like to know about the work atmosphere here…
Would you be able to tell me about this company’s vision/philosophy?
How would you evaluate this organization’s strengths and weaknesses?
I would like to know a little about my day-to-day responsibilities.
Is this an immediate requirement? How soon would you be taking people on board for this position?
I would like to know how my skills compare with the other people who have applied for this position.
I am really interested in this opportunity and I feel I have the required skills for this position. What would I have to do next?
Now that our interview is coming to close, is there anything you would like to know about my ability towards this job?
Would you be able to tell me a little about what the company expects from its employees?
What are the most important assets and skills for this company?
Does the company follow a structured path in promoting the employees? How does it go?
If the company finds me good at the job, how would it advance me? What would be the next step in my career growth?
If I performed well in the current position, what are the additional likely opportunities for me within this company?
Are there any special areas in this company that the top leaders emerge from?/ Are there special areas like say sales or engineering that have more prospects for growth within this company, or do the leaders come from a cross section of different areas?
The company has decided to recruit for this position from outside. How does the company choose between recruiting from within or outside?
How far does this particular position contribute to the bottom line?
What advice would you give to someone selected for this position?
What are the current challenges of this position/department within the company?
Before I leave, can I have a formal/written description of the position? This would help me to review the activities and evaluate what is expected of me.
Is this job likely to lead to other positions in the company? What is the usual route?
Would you be able to tell me a little about the people I will be working with?
Before I take your leave, let me check my understanding of the position. The designation is …., the responsibilities are …., it is in the ….. department, and I would be reporting to ……. Please correct me if I have got it wrong anywhere.
How does this company promote equal opportunity and diversity?
Would you be able to tell me who the company regards as its stars? What have been their most important contributions?
How do the subordinates address their seniors in this company?
Could you tell me about the management style of this company?
If you selected me for this position, what assignment would I be starting on?
Does this company have a formal mission statement? Am I allowed to see it?
What are the most important parameters along which this company evaluates an employee’s contribution?

Some Usefull Question Answers
1. Tell me about yourself?
I am down-to-earth, sweet, smart, creative, industrious, and thorough.
2. How has your experience prepared you for your career?
Coursework:
Aside from the discipline and engineering foundation learning that I have gained from my courses, I think the design projects, reports, and presentations have prepared me most for my career.
Work Experience:
Through internships, I have gained self-esteem, confidence, and problem-solving skills. I also refined my technical writing and learned to prepare professional documents for clients.
Student Organizations:
By working on multiple projects for different student organizations while keeping up my grades, I've built time management and efficiency skills. Additionally, I've developed leadership, communication, and teamwork abilities.
Life Experience:
In general, life has taught me determination and the importance of maintaining my ethical standards.
3. Describe the ideal job.
Ideally, I would like to work in a fun, warm environment with individuals working independently towards team goals or individual goals. I am not concerned about minor elements, such as dress codes, cubicles, and the level of formality. Most important to me is an atmosphere that fosters attention to quality, honesty, and integrity.
4. What type of supervisor have you found to be the best?
I have been fortunate enough to work under wonderful supervisors who have provided limited supervision, while answering thoughtful questions and guiding learning. In my experience, the best supervisors give positive feedback and tactful criticism.
5. What do you plan to be doing in five years' time?
Taking the PE exam and serving in supervisory/leadership roles both at work and in professional/community organization(s).
6. What contributions could you make in this organization that would help you to stand out from other applicants?
In previous internships, my industriousness and ability to teach myself have been valuable assets to the company. My self-teaching abilities will minimize overhead costs, and my industriousness at targeting needs without prompting will set me apart from others. Additionally, one thing that has always set me apart from my scientific/engineering peers are my broad interests and strong writing abilities. I am not your typical "left-brained" engineer, and with my broad talents, I am likely to provide diverse viewpoints.
7. What sort of criteria are you using to decide the organization you will work for?
Most importantly, I am looking for a company that values quality, ethics, and teamwork. I would like to work for a company that hires overachievers.
8. What made you choose your major?
My academic interests are broad, so I sought civil engineering to achieve a great balance of mathematics, chemistry, biology, physics, and writing.
9. Have your university and major met your expectations?
The College of Engineering at MSU has exceeded my expectations by providing group activities, career resources, individual attention, and professors with genuine interest in teaching.
My major has met my expectations by about 90%. I would have enjoyed more choices in environmental courses, and would have preferred more calculus-based learning.
10. What made you choose this college?
I chose this college for the following reasons: my budget limited me to in-state schools, I was seeking an area with dog-friendly apartments, the MSU web site impressed me, I saw active student groups, and the people were very friendly.

How to make your desktop ikons transperent

2008-11-30T14:13:00.000+05:30

Go to ontrol Panel > System, > Advanced > Performance area > Settings button Visual Effects tab "Use drop shadows for icon labels on the Desktop"

Get to the Address bar quick

2008-11-30T14:09:00.000+05:30

To get to the Address bar quickly, press F6. Not only does this move the cursor there, it also highlights the current address so it is deleted with the first key you press.

How to change the Broeser title text

2008-11-30T14:04:00.002+05:30

1.Click Start > Run > Type gpedit.msc
2.Click User Configuration > Windows Setting > Internet Explorer Maintenance > Browser User Interface
3.Double click on Browser Title
4.Click on Customize Title Bars
5.Change the text to what whatever you want
6.Click on Ok

How to rename the recyclebin

2008-11-16T11:16:00.000+05:30

To change the name of the Recycle Bin desktop icon, open Regedit and go to:

HKEY_CLASSES_ROOT/CLSID/{645FF040-5081-101B-9F08-00AA002F954E}

and change the name "Recycle Bin" to whatever you want (don't type any quotes).

Rename a series of files

2008-11-16T11:14:00.000+05:30

When you download photos from your digital camera, they often have unrecognizable names. You can rename several similar files at once with the following procedure. This also works for renaming other types of files.

1.Open the My Pictures folder. (Click Start, and then click My Pictures.) Or open another folder containing files that you want to rename.
2.Select the files you want to rename. If the files you want are not adjacent in the file list, press and hold CTRL, and then click each item to select it.
3.On the File menu, click Rename.
4.Type the new name, and then press ENTER.

All of the files in the series will be named in sequence using the new name you type. For example, if you type Birthday, the first will be named Birthday and subsequent files in the series will be named Birthday (1), Birthday (2), and so on. To specify the starting number for the series, type the starting number in parentheses after the new file name. The files in the series will be numbered in sequence starting with the number you type. For example, if you type Birthday (10), the other files will be named Birthday (11), Birthday (12), and so on.

On screen keyboard

2008-11-16T11:11:00.000+05:30

Want to use an on screen keyboard? Well it is this simple - Click on the start button and select run. Then type in osk in the box and click OK.

How to Hide the Logon Script Dialog Box on a Windows Client

2008-11-16T11:08:00.001+05:30

RESOLUTION

Create a batch file that calls the actual logon script. Using Notepad, create a file that has the following entry:

START /MIN LOGON.BAT

Save the batch file and specify this file as the logon script name for the user accounts in User Manager for Domains. Now, when the users log on to Windows, they will initially run the above batch file, which, in turn, calls the logon script and starts it minimized. The last entry in the real logon script file must be EXIT so the file will close properly.

This works great and solves the problem of users seeing the commands being processed in the actual logon script.

Windows for Workgroups clients do not understand the START command, so this won't work if you have those clients. Also, the initial call to the logon script designated in User Manager for Domains still creates a logon dialog box. The box disappears almost immediately, but may still cause a problemfor the administrator who does not want the user to see anything out of the ordinary when logging on. To have the logon script dialog box minimized during logon and support all clients, do the following:

1.	For the initial preparation, insert a pause statement into the logon script specified in User Manager for Domains. This pause will be important because it is needed to access the properties of the logon script window.
2.	Log on to the workstation as the user in question and, when the logon script pauses, select Properties from the Control menu.
3.	Select the Layout tab in Windows or the Screen Size and Position tab, and set the Width and Height on the Screen Buffer Size and Window Size to 1.
4.	Set the Window Position to 0 for the Left setting and set the Top position to the highest number possible (this will vary depending on the screen resolution). This will put the Window in the lower left-hand corner of the screen.
5.	Select OK after changing the settings and then you will be presented with an Apply Properties dialog box. Select "Save properties for future windows with the same title" and then select OK.
6.	Log off as the user, remove the pause from the logon script, and then log back on. The dialog box is still present, but in the lower left corner of the screen out of the users way.

If, at a later time, you need to resize the windows and cannot access it through the screen, use Registry Editor and delete the following key:

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 (http://support.microsoft.com/kb/322756/) How to back up and restore the registry in Windows

HKEY_CURRENT_USER\Console\_ComputerName_NETLOGON_LogonScript

After that key is deleted, the default dialog box will once again be presented for Windows with that same title.

MORE INFORMATION

Because logon scripts reside in the NetLogon share of every domain controller, the chances are good that you may run the logon script from a different server than the one used in the above example.

Your file is represented in the registry as _ComputerName_NETLOGON_LogonScript. The computer name obviously won't be the same if you are validated by a different controller. Here are two methods to solve this problem.

•

Log on to the workstation as the user in question. Select Start and then Run, or File and then Run, and run the batch file using the UNC path for each of your domain controllers. For example

run \\PDC\NETLOGON\logon.bat

When the file runs, follow steps 3 through 5 above and repeat this for each domain controller (that is. BDC1, BDC2, BDC3, and so on). This will create an entry in the registry for the logon script on each of the possible authenticating servers.

•

You can, when you are logged on as the user in question, run REGEDIT.

Expand the HKEY_CURRENT_USER\Console folder. After going through steps 1 through 6 above, you will see an entry that looks very similar to the following:
_ComputerName_Share_logon.s

Select the key in question, select Registry and then click Export Registry. Give the file a name of your choice. Edit the file using Notepad. It will look like the following:

Copy the above information and paste it below, changing the SERVER name to the name of another authenticating server. Do this for all your domain controllers. The file will now look like the following:

REGEDIT4 [HKEY_CURRENT_USER\Console\__SERVER_NETLOGON_logon.bat] "HistoryNoDup"=dword:00000000 "WindowSize"=dword:0001000d "WindowPosition"=dword:01c00000 "ScreenBufferSize"=dword:0001000d "FontSize"=dword:000c0008 "FontFamily"=dword:00000030 "FontWeight"=dword:00000190 [HKEY_CURRENT_USER\Console\__SERVER2_NETLOGON_logon.bat] "HistoryNoDup"=dword:00000000 "WindowSize"=dword:0001000d "WindowPosition"=dword:01c00000 "ScreenBufferSize"=dword:0001000d "FontSize"=dword:000c0008 "FontFamily"=dword:00000030 "FontWeight"=dword:00000190 [HKEY_CURRENT_USER\Console\__SERVER3_NETLOGON_logon.bat] "HistoryNoDup"=dword:00000000 "WindowSize"=dword:0001000d "WindowPosition"=dword:01c00000 "ScreenBufferSize"=dword:0001000d "FontSize"=dword:000c0008 "FontFamily"=dword:00000030 "FontWeight"=dword:00000190

After you have added an entry for each of your servers, save the file. You can now log on as any user with the same windows resolution and simply double-click this file or import it into the registry using REGEDIT. All users will now have the same window settings on the logon script for any authenticating server.

Direct Bootup Without Typing Password

2008-11-16T11:05:00.000+05:30

1. At a command prompt, type "control userpasswords2" and press Enter to open the Windows 2000-style User Accounts
application.
2. On the Users tab, clear the Users Must Enter A User Name And Password To Use This Computer check box and then
click OK.
3. In the Automatically Log On dialog box that appears, type the user name and password for the account you want to be
logged on each time you start your computer.

Remove Login Password

Control Panel/Administrative Tools/Local Security Settings/Minimum Password Length/Reduce it to 0 (No password required). Control Panel/User Account/Your Account/Remove Password.

Cannot Change the Administrator Password in Control Panel

After you log on as an administrator to a computer that is not a member of a domain, when you double-click User Accounts in Control Panel to change the password for the built-in Administrator account, the Administrator account may not appear in the list of user accounts. Consequently, you cannot change its password.

This behavior can occur because the Administrator account logon option appears only in Safe mode if more than one account is created on the system. The Administrator account is available in Normal mode only if there are no other accounts on the system. To work around this behavior:

- If you are running Windows XP Home Edition, restart the computer and then use a power user account to log on to the
computer in Safe mode.

- If you are running Windows XP Professional, reset the password in the Local Users and Groups snap-in in Microsoft
Management Console (MMC):

1. Click Start, and then click Run.
2. In the Open box, type "mmc" (without the quotation marks), and then click OK to start MMC.
3. Start the Local Users and Groups snap-in.
4. Under Console Root, expand "Local Users and Groups", and then click Users.
5. In the right pane, right-click Administrator, and then click Set Password.
6. Click Proceed in the message box that appears.
7. Type and confirm the new password in the appropriate boxes, and then click OK.

How to Change User Password at Command Prompt

How to use the net user command to change the user password at a Windows command prompt. Only administrators can change domain passwords at the Windows command prompt. To change a user's password at the command prompt, log on as an administrator and type: "net user * /domain" (without the quotation marks)

When you are prompted to type a password for the user, type the new password, not the existing password. After you type the new password, the system prompts you to retype the password to confirm. The password is now changed.

Alternatively, you can type the following command: net user . When you do so, the password changes without prompting you again. This command also enables you to change passwords in a batch file.

Non-administrators receive a "System error 5 has occurred. Access is denied" error message when they attempt to change the password.

How to Enable Automatic Logon in Windows

If you set a computer for auto logon, anyone who can physically obtain access to the computer can gain access to all of the computer contents, including any network or networks it is connected to. In addition, if you enable autologon, the password is stored in the registry in plaintext. The specific registry key that stores this value is remotely readable by the Authenticated Users group.

As a result, this setting is only appropriate for cases where the computer is physically secured, and steps have been taken to ensure that untrusted users cannot remotely access the registry.

1. Start/Run/Regedit, and then locate the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon
2. Using your account name and password, double-click the DefaultUserName entry, type your user name, and then click
OK.
3. Double-click the DefaultPassword entry, type your password, and then click OK.

NOTE: The DefaultPassword value may not exist. If it does not:

a. Click Add Value on the Edit menu.
b. In the Value Name box, type DefaultPassword, and then click REG_SZ for the Data Type
c. Type your password in the String box, and then save your changes.

Also, if no DefaultPassword string is specified, Windows automatically changes the value of the AutoAdminLogon key
from 1 (true) to 0 (false), thus disabling the AutoAdminLogon feature.

4. Click Add Value on the Edit menu, enter AutoAdminLogon in the Value Name box, and then click REG_SZ for the Data
Type.
5. Type "1" (without the quotation marks) in the String box, and then save your changes.
6. Quit Regedit.
7. Click Start, click Shutdown, and then click OK to turn off your computer.
8. Restart your computer and Windows. You are now able to log on automatically.

NOTE: To bypass the AutoAdminLogon process, and to log on as a different user, hold down the SHIFT key after you log off or after Windows restarts.

Note that this procedure only applies to the first logon. To enforce this setting for subsequent logoffs, the administrator must set the following registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon

Value: ForceAutoLogon
Type: REG_SZ
Data: 1

Windows XP Inherits Autologon Setting After Upgrade from Win2000

After you upgrade a Microsoft Windows 2000-based computer, Windows XP Professional may start directly to the desktop without stopping at the Welcome screen or requiring you to type a username and password. If you then create a new user account, you may not receive any option that allows you to log on by using the new account.

This behavior can occur if Windows 2000 was configured for automatic logon (Autologon). Windows XP inherits this configuration setting.

To resolve this behavior, turn off the automatic logon feature and require a username and password at logon:

1. Click Start on the Windows taskbar, and then click Run.
2. In the Open box, type control userpasswords2, and then click OK.
3. In the dialog box that appears, click to select the "Users must enter a user name and password to use this computer"
check box, and then click OK.

To work around this behavior, log off from the Autologon account, and then log on by using the new account.

Not Prompted to Create Password with New XP User Account

When you create a new user on a Microsoft Windows XP Home Edition-based computer, you are not prompted to create a password. To create a password for a user account, click the icon for the account, and then click "Create a Password".

Stored User Names and Passwords Feature Interoperability at a Command Prompt

By default, the Stored User Names and Passwords feature creates a "key" for any connection that you make in the graphical user interface (GUI) that requires alternate credentials. When you make a connection at a command prompt by using the net use command and by passing alternate credentials, a key is not created.

For the net use command to save the credentials in Credential Manager, use the /savecred switch. When you use the /savecred switch, any credentials that you are prompted for when you use the net use command are saved as a key.

Therefore, if you are prompted for the user name and password (or if you are prompted only for the password) when you use the net use command (but not because you used an asterisk [*] in the net use command for password prompting) and the /savecred switch, the credentials are saved.

When you type the net use * \\ computer_name \ share_name /savecred command, the user is prompted for a user name, and then the user is prompted for a password.

When you type the net use * \\ computer_name \ share_name /u: domain_name \ user_name /savecred command, the user is prompted for a password.

However, when you type one of the following commands, a key is not created:
net use * \\ computer_name \ share_name * /user: domain_name \ user_name /savecred
-or-
net use * \\ computer_name \ share_name * /savecred /user: domain_name \ user_name

If you type net help use at a command prompt, more information is displayed about the net use command.

Password Has Expired Message

Start/Programs/Administrative Tools/Local Security Policy/Account Policies/Password Policy. In the right pane, right click, properties, modify (use accordingly). And Start/Programs/Administrative Tools/Computer Management/Local Users and Groups/Right Click "User"(intended)/Properties...Or with Admin privileges, at a command prompt type: net accounts /maxpwage:unlimited.

To Create a Password Reset Disk

The Forgotten Password Wizard lets you create a password reset disk that you can use to recover your user account and personalized computer settings if you forget your password. The steps to perform this task differ depending on whether your computer is a member of a network domain or is part of a workgroup (or is a stand-alone computer).

My Computer is on a Domain

Press CTRL+ALT+DELETE to open the Windows Security dialog box. Click Change Password.
Click Backup to open the Forgotten Password Wizard. Click Next and then follow the instructions as they appear on the screen.

My Computer is not on a Domain

The steps to perform this task differ depending on the type of user account you have. If you have a computer administrator account: Open User Accounts in Control Panel. Click your account name. Under Related Tasks located on the left side of the window, click Prevent a forgotten password. In the Forgotten Password Wizard, follow the instructions as they appear on the screen.

If you Have a Limited Account

Open User Accounts in Control Panel. Under Related Tasks located on the left side of the window, click Prevent a forgotten password. In the Forgotten Password Wizard, follow the instructions as they appear on the screen.

Notes: To open User Accounts, click Start, point to Settings, click Control Panel, and then click User Accounts.

Certain Programs Do Not Work Correctly If You Log On Through a Limited User Account.

After you log on to a computer by using a Limited User Account, you may observe one or more of the following
behaviors when you try to use a program that is not expressly designed for Windows XP. Information here.

Password Reset Disk Overview

To protect user accounts in the event that the user forgets the password, every local user should make a password reset disk and keep it in a safe place. Then, if the user forgets his or her password, the password can be reset using the password reset disk and the user is able to access the local user account again.

Resetting the Password

After you reset the password of an account on a Windows XP-based computer that is joined to a workgroup, you may lose access to the user's: Web page credentials, File share credentials, EFS-encrypted files, Certificates with private keys (SIGNED/ENCRYPTed e-mail). More information in detail here.

I assume no responsibility for the purpose to which this information is used. This includes employees attempting to bypass restrictions put into place by System Administrators on corporate machines.

Delete Admin Password

Boot up with DOS and delete the sam.exe and sam.log files from Winnt\system32\config in your hard drive. Now when you boot up in NT the password on your built-in administrator account will be blank (No password). This solution works only if your hard drive is FAT. [Editor's note: Use with caution, there may be other ramifications from performing this tip.]

Forgot your Admin Password

This is a utility to (re)set the password of any user that has a valid (local) account on your NT system, by modifying the crypted password in the registrys SAM file. You do not need to know the old password to set a new one.

It works offline, that is, you have to shutdown your computer and boot off a floppydisk. The bootdisk includes stuff to access NTFS partitions and scripts to glue the whole thing together. Note: It will now also work with SYSKEY, including the option to turn it off! More information here. Download here.

All Passwords-Master Copy

With Darn! Passwords! Just one password opens the safe that holds all those other ones for programs and web sites that require you to log in. Download Here.

Just pick the password, and drag it and it's log-in (if there is one) into the program that uses it. No retyping is necessary (even in programs that do not accept the drag, you can just paste the password in). Go to the URL of a password protected site with the click of a button.

Information on System Restore and Password Restoration

Passwords That Are Restored:

1. Program passwords are restored, such as Hotmail Messenger, AOL Messenger, Yahoo Messenger, and other Web server-based passwords. This behavior is by design: The programs simply cache these passwords; the actual passwords are
stored on a Web server. System Restore does not actually change the password, but it changes the password that is remembered by the program. You can use the current password for the program to log on to the server.

2. Domain and Computer passwords are restored. This behavior is by Design and is a limitation of System Restore. System Restore only rolls back the local machine state. Part of the information about joining domains resides in Active Directory, and Active Directory is not rolled back by System Restore.

Migration Wizard Does Not Migrate Passwords

The Migration Wizard does not migrate passwords. Passwords for Dial-Up Networking connections, Microsoft Outlook Express accounts, Microsoft Internet Explorer saved passwords, mapped drives, and so on will need to be reconfigured once the migration is complete.

Administrator Account Not Used for Logon

The administrator account and password created during Setup are used to log on in Safe Mode only. To create a password for user accounts, double-click Manage Users in Control Panel.

Logon Name Not in Task Manager or Under Documents & Settings

When the Welcome screen is appears, the names that are displayed do not match any of the names of users' folders under the Documents and Settings folder or any of the names on the Users tab in Task Manager.

This behavior may occur if you have changed the name of the account in the User Accounts tool in Control Panel. By doing so, the new name appears on the Welcome screen, but the actual account name remains the same. The folders under the Documents and Settings folder and the names that are listed in Task Manager show the actual account name.

To resolve this behavior, if the display name for a user account has been changed, you can find out which account the new display name belongs to by logging on as that user, starting Task Manager, and then clicking the Users tab.

The user account that is marked as active is the one that is currently logged on. Also, you can find out which of the folders under Documents and Settings belongs to the currently logged-on user by right-clicking Start, and then clicking Explore. Windows Explorer will then start in the Start Menu folder of the currently logged-on user's folder.

Administrator Unable to Unlock a "Locked" Computer

This behavior can occur for either of the following reasons: When the default screen saver is set to use a non-existent screen saver program. And/or When you use a corrupted screen saver that is password protected. More Information.

Information About Unlocking a Workstation

The following registry setting is received every time the computer is locked: Start/Run/Regedit

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

ForceUnlockLogon
REG_DWORD

0 - Do not force authentication inline (default)
1 - Require online authentication to unlock

The preceding value controls whether a full logon is performed during the unlock process. This can force a validation at the domain controller for the user attempting the unlock process.

NOTE: If the value is not present, it functions as if it had been set to 0 (zero).

Lock Your Computer and Use Other Windows Logo Shortcut Keys

To use the shortcut, press the Windows logo key+L. The following list has different computer lock-up scenarios that are available to you, as well as other ways to lock the computer: Click Here.

Create a Shortcut to Lock Computer

Right click a blank space on the desktop, select new, shortcut. Copy and Paste this line: "rundll32.exe user32.dll,LockWorkStation" in the program location box. Click next and create a name for your shortcut, click finish.

Lock the Taskbar

This restriction is used to force the locking of the taskbar and restrict users from making any changes to its position. Start/Run/Regedit: Navigate to this key and create a new DWORD value, or modify the existing value, called 'LockTaskbar' and edit the value according to the settings below. Exit your registry, you may need to restart or log out of Windows for the change to take effect.

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
Value Name: LockTaskbar
Data Type: REG_DWORD (DWORD Value)
Value Data: (0 = Unlocked, 1 = Locked)

Formatting hard drive

2008-11-16T11:01:00.001+05:30

Now to begin, you will need a MS Dos6.xx or Windows9x boot disk.

STEP ONE
You first need to decide what operating system you intend to load after formatting the hard drive. It is best and easiest to use a boot disk for that Operating System, such as MS Dos6.2 or Windows95b or Windows98SE. You will need the proper Windows95/98 boot disk in order to load the these operating systems on the computer, else it will reject loading due to the wrong Operating System on the computer.

STEP TWO
Insert your boot disk in the floppy drive and start the computer. Once the system has completed booting and an A: prompt appears we are ready to start.

Type: format C: /s [press Enter]

This statement tells the system to format your "C" drive and when it is finished to copy the system files to the drive, (the /s switch for 'System'). You can format a different drive this way by using a different drive letter.

Format should display: WARNING, ALL DATA ON
NON-REMOVABLE DISK DRIVE C: WILL BE LOST!
Proceed with Format (Y/N)? Type [Y] [Press ENTER]

Your screen should display the size of your drive and a countdown in percentage of formatting completed. Depending on your computer's speed and the size of the drive it can take from a few minutes to over 15minutes.

STEP THREE
When it reaches 100% complete, you will see a new message:
FORMAT COMPLETE. SYSTEM TRANSFERRED.

This indicates that the files required to boot your computer from the hard drive have been copied from the floppy to the hard drive. The computer can now boot from the hard drive without a boot disk in the floppy drive.

You will see one last message:
Volume label (11 characters, ENTER for none)?
Type anything you like or leave it blank - [Press ENTER]

You can now begin to load your Operating System

Special Note:
You may receive the error message:
"insufficient memory to load system files"

This is caused by the lack of a memory manager loaded at boot and your PC can only access the first 1mg of ram memory. There are two possible solutions:

1) Omit the /s switch when formatting. This is done by typing this:
FORMAT C: [press enter]

Then when the format is complete, manually add the system files to your hard drive by using this command:
SYS C: [press enter]

2) You will need to load a memory manager in order to overcome this issue. Not knowing what operating system boot disk you are using is an issue here. However, Windows98 boot disks load a memory manager, so let us assume it is either Windows95 or earlier.

You need to add the file HIMEM.SYS to your boot disk and then modify your Config.sys file on the boot disk.

Download HIMEM.SYS 10k

Unzip the file to your boot disk and add this line in the Config.sys, (make this the first line):

DEVICE=himem.sys

Now, reboot your computer with the boot disk and it should work fine.

You will find that the boot disks we offer for download are all configured with a Memory manager and contain the file: HIMEM.SYS

Partitioning a hard drive

2008-11-16T10:55:00.001+05:30

Removing an existing Partition

Now to begin, you will need a MS Dos6.xx or Windows9x boot disk.

Step One
Insert your Windows95/98 Startup Disk (or DOS 6 boot disk) in the A: Drive. Turn on the computer with the floppy disk drive in the A: drive.

When the computer has finished booting you should be at the A: Prompt. (If your computer still boots to the C: drive or continues to load into Windows, then you make sure the boot sequence of the computers BIOS/CMOS is set to boot from the floppy drive, (A,C) first.)

Step Two
From the A: prompt type: FDISK [Press-Enter]

Windows95b(OSR2) and Win98 will give you this prompt:

Do you wish to enable large disk support (Y/N)..? [Y]

(Yes is 32bit fat and NO is 16bit fat) If you wish a partition larger than 2gigs, choose [Y]. See our FAQ 16bit partitions vs 32bit partitions.

IMPORTANT: If you enable large disk support and create any new drives on this disk, you will not be able to access the new drive(s) using other operating systems, including some versions of Windows 95 and Windows NT, as well as earlier versions of Windows and MS-DOS. In addition, disk utilities that were not designed explicitly for the FAT32 file system will not be able to work with this disk. If you need to access this disk with other operating systems or older disk utilities, do not enable large drive support.

Now this screen will appear:

Press 3 and then press [Enter]. At this point it is all very simple. Just begin by selecting the partition you wish deleted and follow the instructions on the screen.

Creating a New Partition

Step One
Insert your Windows95/98 Startup Disk (or DOS 6 boot disk) in the A: Drive. Turn on the computer with the floppy disk drive in the A: drive.

Step Two
From the A: prompt type: FDISK [Press-Enter]

Windows95b(OSR2) and Win98 will give you this prompt:

Do you wish to enable large disk support (Y/N)..? [Y]

(Yes is 32bit fat and NO is 16bit fat) If you wish a partition larger than 2gigs, choose [Y]. See our FAQ 16bit partitions vs 32bit partitions.

Now this screen will appear:

STEP THREE
First thing to do is determine if you have a partition on the hard drive. Choose 4 and [Press Enter] If you are ready to proceed, this screen will display a message of: "No paritions defined." [Press Esc] to return to the previous screen. NOTE: If any partitions are displayed you will need to delete them to proceed.

Now, we have no partitions on the drive, Choose 1 and [Press Enter].

Now this screen will appear:

Choose 1 and [Press Enter].

STEP FOUR
Now, a screen will appear with this question:

Do you if you want to partition the full size of the drive? Choose [Y] and [Press ENTER]

You will be asked "Do you wish to Set the Partition as Active?" Choose [Y] and [Press Enter]

When FDISK has finished creating the partition:
[press ESC] and exit FDISK. Your system must reboot inorder for it to use the new partition. Time now to REBOOT.

How to write CD

2008-11-16T10:40:00.001+05:30

•Insert a blank, writable CD into the CD recorder.

•Open My Computer.

•Click the files or folders you want to copy to the CD. To select more than one file, hold down the CTRL key while you click the files you want. Then, under File and Folder Tasks, click Copy this file, Copy this folder, or Copy the selected items.

•If the files are located in My Pictures, under Picture Tasks, click Copy to CD or Copy all items to CD, and then skip to step 5.

•In the Copy Items dialog box, click the CD recording drive, and then click Copy.

•In My Computer, double–click the CD recording drive. Windows displays a temporary area where the files are held before they are copied to the CD. Verify that the files and folders that you intend to copy to the CD appear under Files Ready to be Written to the CD.

•Under CD Writing Tasks, click Write these files to CD. Windows displays the CD Writing Wizard. Follow the instructions in the wizard.

Notes:

•Do not copy more files to the CD than it will hold. Standard CDs hold up to 650 megabytes (MB). High–capacity CDs hold up to 850 MB.

•Be sure that you have enough disk space on your hard disk to store the temporary files that are created during the CD writing process. For a standard CD, Windows reserves up to 700 MB of the available free space. For a high–capacity CD, Windows reserves up to 1 gigabyte (GB) of the available free space.

•After you copy files or folders to the CD, it is useful to view the CD to confirm that the files are copied. For more information, click Related Topics.

To stop the CD recorder from automatically ejecting the CD

•Open My Computer.

•Right–click the CD recording drive, and then click Properties.

•On the Recording tab, clear the Automatically eject the CD after writing check box.

Simplify using ur mouse change double click to single-click

2008-10-13T17:59:00.004+05:30

When you browse the Web with Microsoft Internet Explorer, links open with a single click. Yet, when you browse My Computer or My Documents, a single click lets you select a file or folder, but you have to double-click to open it.

If you'd rather single-click to open files and folders, you can change the setting on your mouse (don't worry, this process doesn't require any double clicks).

To change the settings on your mouse

Click Start, and then click My Computer.

Click Tools, and then click Folder Options.

Click Single-click to open an item. Then, click OK.

Now you can navigate folders and open files with a single rather than a double click. If you need to select a file, simply hold your mouse over the file for a few seconds without clicking.

Create a keyboard shortcut to open a folder

2008-10-13T17:56:00.000+05:30

Do you have a folder that you'd like to be able to open quickly and easily whenever you want? If you create a keyboard shortcut for that folder, you can open it anytime by pressing a key combination, no matter which other programs you have open.

To create a keyboard shortcut to open a folder

1.	Click on Start, All Programs, Accessories, and then click Windows Explorer.
2.	In Windows Explorer (the program that appears when you open folders such as My Computer, My Documents, My Pictures, or My Music), right-click the folder to which you want instant access, click Send To, and then click Desktop.
3.	On your desktop, right-click the new shortcut, and then click Properties.
4.	On the Shortcut tab, click in the Shortcut key box. Now press the letter on your keyboard that you want to use to open the folder. Note: In the Shortcut key box, Microsoft Windows XP automatically adds CTRL+ALT before the key you press, because to use the shortcut to open a folder, you have to hold down both the CTRL and ALT keys simultaneously, while pressing the letter you chose. This way, your folder won't open every time you type that letter.
5.	Click OK.
6.	Now test your shortcut. Hold down the CTRL and ALT keys, and then press the letter you chose.

Tired of chasing your mouse? Use keyboard shortcuts

2008-10-13T17:51:00.003+05:30

The mouse, one of the greatest advances in computing history, provides you with an intuitive point-and-click method for using your computer. Depending on the type of work you're doing, however, sometimes using a mouse actually slows you down. If you are a good typist, taking your hands away from the keyboard to move the mouse can use up a few seconds. Over the course of a full day, you could save several minutes by using keyboard shortcuts instead of the mouse.

You can use your keyboard instead of your mouse to do these three tasks:

•	Start a program
•	Navigate menus
•	Minimize, maximize, and close windows

Start a program using a keyboard shortcut

The Start menu is great for finding programs, but its multiple levels of folders can be time consuming to navigate. If there is a program you start frequently, you should set a keyboard shortcut for it so that you can start the program without taking your hands off the keyboard.

To set a keyboard shortcut to start a program

1.	Click the Start menu, and then click All Programs. Right-click the program that you want to start with a keyboard shortcut, and then click Properties.
2.	Click in the Shortcut key box. Now press the letter on your keyboard that you want to use to start the program. Make it easy to remember—for example, press I for Microsoft Internet Explorer. Note: You can use either uppercase or lowercase letters when creating your keyboard shortcuts—and when accessing them later. In the Shortcut key box, Microsoft Windows XP automatically adds Ctrl + Alt + before the key you pressed. When you want to start the program, hold down both the CTRL and ALT keys simultaneously, while also pressing the letter you chose. This way, your program won't start every time you type that letter.
3.	Click OK.
4.	Now test your shortcut. Hold down the CTRL and ALT keys, and then press the letter you chose. If you find it difficult to hold down two keys at once, read Turn on the Sticky Keys feature. Your program should start.

When your friends see you start up programs without touching your mouse, they just might think you have a psychic connection with your computer!

Top of page

Navigate menus using the keyboard

You can speed up tasks in almost any program by choosing menu items using your keyboard instead of your mouse. This operation is particularly handy when you're performing repetitive tasks.

To control menus using your keyboard

With your program open, press the ALT key. Notice that one letter on each menu name is now underlined. To open the menu, press the underlined key. For example, in Internet Explorer, the View menu name shows the V underlined after you press the ALT key. To open the View menu, press the ALT key, and then press V.

Now, each menu item will show one letter underlined. To access or activate the menu item you want, simply press the underlined key. For example, in Internet Explorer, after you open the View menu, the Privacy Report menu item shows the V underlined. Instead of clicking Privacy Report with your mouse, you can just press the V key.

You can also choose menu commands by pressing key sequences quickly, without waiting for the menus to open. For example, to quickly view a Web page's privacy report in Internet Explorer, press ALT, V, V. Similarly, to save a Web page in Internet Explorer, you would normally click the File menu, and then click Save As. To choose the same commands using your keyboard, press ALT, F, A.

Top of page

Control windows using your keyboard

If you like to keep four or five windows open while you work (or play) on your computer, you'll appreciate knowing these keyboard shortcuts. You can quickly switch between your Web browser, e-mail, instant message windows, and other programs without taking your hands off the keyboard.

Action	Shortcut
Minimize a window to your taskbar	ALT, SPACEBAR, N
Maximize a window so it takes up your whole desktop	ALT, SPACEBAR, X
Restore a window so it's visible but doesn't take up your whole desktop	ALT, SPACEBAR, R
Close a window	ALT+F4
Switch to the last window you had open	ALT+TAB
Switch to any window	Hold down the ALT key, and press TAB until the window you want is active

Programs often start up in a "restored" state, where the window takes up only part of the screen. To maximize the window so that it takes up the entire screen, press the ALT key, press the SPACEBAR, and then press X. This will feel natural after you do it a few times, and you will feel much more efficient while using your computer.

How to draw the circuit diagrams

2008-10-11T18:39:00.004+05:30

Drawing circuit diagrams

Drawing circuit diagrams is not difficult but it takes a little practice to draw neat, clear diagrams. This is a useful skill for science as well as for electronics. You will certainly need to draw circuit diagrams if you design your own circuits.
Follow these tips for best results:

Make sure you use the correct symbol for each component.
Draw connecting wires as straight lines (use a ruler).
Put a 'blob' () at each junction between wires.
Label components such as resistors and capacitors with their values.
The positive (+) supply should be at the top and the negative (-) supply at the bottom. The negative supply is usually labelled 0V, zero volts.
If you are drawing the circuit diagram for science please see the section about drawing diagrams the "electronics way".

If the circuit is complex:

Try to arrange the diagram so that signals flow from left to right: inputs and controls should be on the left, outputs on the right.
You may omit the battery or power supply symbols, but you must include (and label) the supply lines at the top and bottom.

Drawing circuit diagrams the 'electronics way'

Circuit diagrams for electronics are drawn with the positive (+) supply at the top and the negative (-) supply at the bottom. This can be helpful in understanding the operation of the circuit because the voltage decreases as you move down the circuit diagram.

Circuit diagrams for science are traditionally drawn with the battery or power supply at the top. This is not wrong, but there is usually no advantage in drawing them this way and I think it is less helpful for understanding the circuit.

I suggest that you always draw your circuit diagrams the 'electronics way', even for science!

Quantities and units

2008-10-11T18:27:00.002+05:30

Quantities

The table shows electrical quantities which are used in electronics.
The relationship between quantities can be written using words or symbols (letters), but symbols are normally used because they are much shorter; for example V is used for voltage, I for current and R for resistance:
As a word equation:
voltage = current × resistance

The same equation using symbols: V = I × R
To prevent confusion we normally use the same symbol (letter) for each quantity and these symbols are shown in the second column of the table

Quantity	Usual Symbol	Unit	Unit Symbol
Voltage	V	volt	V
Current	I	amp*	A
Charge	Q	coulomb	C
Resistance	R	ohm
Capacitance	C	farad	F
Inductance	L	henry	H
Reactance	X	ohm
Impedance	Z	ohm
Power	P	watt	W
Energy	E	joule	J
Time	t	second	s
Frequency	f	hertz	Hz
* strictly the unit is ampere, but this is almost always shortened to amp.

Units

The first table shows the unit (and unit symbol) which is used to measure each quantity. For example: Charge is measured in coulombs and the symbol for a coulomb is C.
Some of the units have a convenient size for electronics, but most are either too large or too small to be used directly so they are used with the prefixes shown in the second table. The prefixes make the unit larger or smaller by the value shown.

Some examples:
25 mA = 25 × 10^-3 A = 25 × 0.001 A = 0.025 A
47µF = 47 × 10^-6 F = 47 × 0.000 001 F = 0.000 047 F
270k = 270 × 10³ = 270 × 1000 = 270 000

Why not change the units to be better sizes?

It might seem a good idea to make the farad (F) much smaller to avoid having to use µF, nF and pF, but if we did this most of the equations in electronics would have to have factors of 1000000 or more included as well as the quantities. Overall it is much better to have the units with their present sizes which are defined logically from the equations.
In fact if you use an equation frequently you can use special sets of prefixed units which are more convenient... For example: Ohm's Law, V = I × R
the standard units are volt (V), amp (A) and ohm (),
but you could use volt (V), milliamp (mA) and kilo-ohm (k) if you prefer.
Take care though, you must never mix sets of units: using V, A and k in Ohm's Law would give you wrong

Prefix	Prefix Symbol	Value
milli	m	10^-3	= 0.001
micro	µ	10^-6	= 0.000 001
nano	n	10^-9	= 0.000 000 001
pico	p	10^-12	= 0.000 000 000 001
kilo	k	10³	= 1000
mega	M	10⁶	= 1000 000
giga	G	10⁹	= 1000 000 000
tera	T	10¹²	= 1000 000 000 000

555 & 556 Timer circuits

2008-10-11T18:14:00.002+05:30

Introduction

Example circuit symbol (above)

Actual pin arrangements (below)

The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. With just a few external components it can be used to build many circuits, not all of them involve timing!
A popular version is the NE555 and this is suitable in most cases where a '555 timer' is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams on this page show a 555, but they could all be adapted to use one half of a 556.
Low power versions of the 555 are made, such as the ICM7555, but these should only be used when specified (to increase battery life) because their maximum output current of about 20mA (with a 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555.
The circuit symbol for a 555 (and 556) is a box with the pins arranged to suit the circuit diagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually just the pin numbers are used and they are not labelled with their function.
The 555 and 556 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum).Standard 555 and 556 ICs create a significant 'glitch' on the supply when their output changes state. This is rarely a problem in simple circuits with no other ICs, but in more complex circuits a smoothing capacitor (eg 100µF) should be connected across the +Vs and 0V supply near the 555 or 556.
The input and output pin functions are described briefly below and there are fuller explanations covering the various circuits:

Astable - producing a square wave
Monostable - producing a single pulse when triggered
Bistable - a simple memory which can be set and reset
Buffer - an inverting buffer (Schmitt trigger)

Inputs of 555/556

Trigger input: when < ¹/₃ Vs ('active low') this makes the output high (+Vs). It monitors the discharging of the timing capacitor in an astable circuit. It has a high input impedance > 2M.
Threshold input: when > ²/₃ Vs ('active high') this makes the output low (0V)*. It monitors the charging of the timing capacitor in astable and monostable circuits. It has a high input impedance > 10M.
* providing the trigger input is > ¹/₃ Vs, otherwise the trigger input will override the threshold input and hold the output high (+Vs).

Reset input: when less than about 0.7V ('active low') this makes the output low (0V), overriding other inputs. When not required it should be connected to +Vs. It has an input impedance of about 10k.
Control input: this can be used to adjust the threshold voltage which is set internally to be ²/₃ Vs. Usually this function is not required and the control input is connected to 0V with a 0.01µF capacitor to eliminate electrical noise. It can be left unconnected if noise is not a problem.

The discharge pin is not an input, but it is listed here for convenience. It is connected to 0V when the timer output is low and is used to discharge the timing capacitor in astable and monostable circuits.

Output of 555/556

The output of a standard 555 or 556 can sink and source up to 200mA. This is more than most ICs and it is sufficient to supply many output transducers directly, including LEDs (with a resistor in series), low current lamps, piezo transducers, loudspeakers (with a capacitor in series), relay coils (with diode protection) and some motors (with diode protection). The output voltage does not quite reach 0V and +Vs, especially if a large current is flowing.
To switch larger currents you can connect a transistor.The ability to both sink and source current means that two devices can be connected to the output so that one is on when the output is low and the other is on when the output is high. The top diagram shows two LEDs connected in this way. This arrangement is used in the Level Crossing project to make the red LEDs flash alternately.

Loudspeakers

A loudspeaker (minimum resistance 64) may be connected to the output of a 555 or 556 astable circuit but a capacitor (about 100µF) must be connected in series. The output is equivalent to a steady DC of about ½Vs combined with a square wave AC (audio) signal. The capacitor blocks the DC, but allows the AC to pass as explained in capacitor coupling.

Piezo transducers may be connected directly to the output and do not require a capacitor in series.

Relay coils and other inductive loads

Like all ICs, the 555 and 556 must be protected from the brief high voltage 'spike' produced when an inductive load such as a relay coil is switched off. The standard protection diode must be connected 'backwards' across the the relay coil as shown in the diagram. However, the 555 and 556 require an extra diode connected in series with the coil to ensure that a small 'glitch' cannot be fed back into the IC. Without this extra diode monostable circuits may re-trigger themselves as the coil is switched off! The coil current passes through the extra diode so it must be a 1N4001 or similar rectifier diode capable of passing the current, a signal diode such as a 1N4148 is usually not suitable

555/556 Astable

555 astable output, a square wave
(Tm and Ts may be different)

555 astable circuit

An astable circuit produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). Note that the durations of the low and high states may be different. The circuit is called an astable because it is not stable in any state: the output is continually changing between 'low' and 'high'.
The time period (T) of the square wave is the time for one complete cycle, but it is usually better to consider frequency (f) which is the number of cycles per second.

T = 0.7 × (R1 + 2R2) × C1 and f =	1.4
	(R1 + 2R2) × C1

T = time period in seconds (s)
f = frequency in hertz (Hz)
R1 = resistance in ohms ()
R2 = resistance in ohms ()
C1 = capacitance in farads (F)

The time period can be split into two parts: T = Tm + Ts
Mark time (output high): Tm = 0.7 × (R1 + R2) × C1
Space time (output low): Ts = 0.7 × R2 × C1
Many circuits require Tm and Ts to be almost equal; this is achieved if R2 is much larger than R1.

For a standard astable circuit Tm cannot be less than Ts, but this is not too restricting because the output can both sink and source current. For example an LED can be made to flash briefly with long gaps by connecting it (with its resistor) between +Vs and the output. This way the LED is on during Ts, so brief flashes are achieved with R1 larger than R2, making Ts short and Tm long. If Tm must be less than Ts a diode can be added to the circuit as explained under duty cycle below.

Choosing R1, R2 and C1

555 astable frequencies
C1	R2 = 10k R1 = 1k	R2 = 100k R1 = 10k	R2 = 1M R1 = 100k
0.001µF	68kHz	6.8kHz	680Hz
0.01µF	6.8kHz	680Hz	68Hz
0.1µF	680Hz	68Hz	6.8Hz
1µF	68Hz	6.8Hz	0.68Hz
10µF	6.8Hz	0.68Hz (41 per min.)	0.068Hz (4 per min.)

R1 and R2 should be in the range 1k to 1M. It is best to choose C1 first because capacitors are available in just a few values.

Choose C1 to suit the frequency range you require (use the table as a guide).
Choose R2 to give the frequency (f) you require. Assume that R1 is much smaller than R2 (so that Tm and Ts are almost equal), then you can use:
R2 = 0.7

f × C1
Choose R1 to be about a tenth of R2 (1k min.) unless you want the mark time Tm to be significantly longer than the space time Ts.
If you wish to use a variable resistor it is best to make it R2.
If R1 is variable it must have a fixed resistor of at least 1k in series
(this is not required for R2 if it is variable).

Astable operation

With the output high (+Vs) the capacitor C1 is charged by current flowing through R1 and R2. The threshold and trigger inputs monitor the capacitor voltage and when it reaches ²/₃Vs (threshold voltage) the output becomes low and the discharge pin is connected to 0V.

The capacitor now discharges with current flowing through R2 into the discharge pin. When the voltage falls to ¹/₃Vs (trigger voltage) the output becomes high again and the discharge pin is disconnected, allowing the capacitor to start charging again.

This cycle repeats continuously unless the reset input is connected to 0V which forces the output low while reset is 0V.
An astable can be used to provide the clock signal for circuits such as counters.
A low frequency astable (< 10Hz) can be used to flash an LED on and off, higher frequency flashes are too fast to be seen clearly. Driving a loudspeaker or piezo transducer with a low frequency of less than 20Hz will produce a series of 'clicks' (one for each low/high transition) and this can be used to make a simple metronome.
An audio frequency astable (20Hz to 20kHz) can be used to produce a sound from a loudspeaker or piezo transducer. The sound is suitable for buzzes and beeps. The natural (resonant) frequency of most piezo transducers is about 3kHz and this will make them produce a particularly loud sound.

Duty cycle

The duty cycle of an astable circuit is the proportion of the complete cycle for which the output is high (the mark time). It is usually given as a percentage.

For a standard 555/556 astable circuit the mark time (Tm) must be greater than the space time (Ts), so the duty cycle must be at least 50%:

Duty cycle =	Tm	=	R1 + R2
	Tm + Ts		R1 + 2R2

555 astable circuit with diode across R2

To achieve a duty cycle of less than 50% a diode can be added in parallel with R2 as shown in the diagram. This bypasses R2 during the charging (mark) part of the cycle so that Tm depends only on R1 and C1:

Tm = 0.7 × R1 × C1 (ignoring 0.7V across diode)
Ts = 0.7 × R2 × C1 (unchanged)

Duty cycle with diode =	Tm	=	R1
	Tm + Ts		R1 + R2

Use a signal diode such as 1N4148.

555/556 Monostable

555 monostable output, a single pulse

555 monostable circuit with manual trigger

A monostable circuit produces a single output pulse when triggered. It is called a monostable because it is stable in just one state: 'output low'. The 'output high' state is temporary.
The duration of the pulse is called the time period (T) and this is determined by resistor R1 and capacitor C1:

time period, T = 1.1 × R1 × C1

T = time period in seconds (s)
R1 = resistance in ohms ()
C1 = capacitance in farads (F)
The maximum reliable time period is about 10 minutes.

Why 1.1? The capacitor charges to ²/₃ = 67% so it is a bit longer than the time constant (R1 × C1) which is the time taken to charge to 63%.

Choose C1 first (there are relatively few values available).
Choose R1 to give the time period you need. R1 should be in the range 1k to 1M, so use a fixed resistor of at least 1k in series if R1 is variable.
Beware that electrolytic capacitor values are not accurate, errors of at least 20% are common.
Beware that electrolytic capacitors leak charge which substantially increases the time period if you are using a high value resistor - use the formula as only a very rough guide!
For example the Timer Project should have a maximum time period of 266s (about 4½ minutes), but many electrolytic capacitors extend this to about 10 minutes!

Monostable operation

The timing period is triggered (started) when the trigger input (555 pin 2) is less than ¹/₃ Vs, this makes the output high (+Vs) and the capacitor C1 starts to charge through resistor R1. Once the time period has started further trigger pulses are ignored.

The threshold input (555 pin 6) monitors the voltage across C1 and when this reaches ²/₃ Vs the time period is over and the output becomes low. At the same time discharge (555 pin 7) is connected to 0V, discharging the capacitor ready for the next trigger.
The reset input (555 pin 4) overrides all other inputs and the timing may be cancelled at any time by connecting reset to 0V, this instantly makes the output low and discharges the capacitor. If the reset function is not required the reset pin should be connected to +Vs.

Power-on reset or
trigger circuit

Power-on reset or trigger

It may be useful to ensure that a monostable circuit is reset or triggered automatically when the power supply is connected or switched on. This is achieved by using a capacitor instead of (or in addition to) a push switch as shown in the diagram.
The capacitor takes a short time to charge, briefly holding the input close to 0V when the circuit is switched on. A switch may be connected in parallel with the capacitor if manual operation is also required.
This arrangement is used for the trigger in the Timer Project.

Edge-triggering

edge-triggering circuit

If the trigger input is still less than ¹/₃ Vs at the end of the time period the output will remain high until the trigger is greater than ¹/₃ Vs. This situation can occur if the input signal is from an on-off switch or sensor.
The monostable can be made edge triggered, responding only to changes of an input signal, by connecting the trigger signal through a capacitor to the trigger input. The capacitor passes sudden changes (AC) but blocks a constant (DC) signal. For further information please see the page on capacitance. The circuit is 'negative edge triggered' because it responds to a sudden fall in the input signal. The resistor between the trigger (555 pin 2) and +Vs ensures that the trigger is normally high (+Vs).

555/556 Bistable (flip-flop) - a memory circuit

555 bistable circuit

The circuit is called a bistable because it is stable in two states: output high and output low. It is also known as a 'flip-flop'.
It has two inputs:

Trigger (555 pin 2) makes the output high.
Trigger is 'active low', it functions when < ¹/₃ Vs.
Reset (555 pin 4) makes the output low.
Reset is 'active low', it resets when <>

The power-on reset, power-on trigger and edge-triggering circuits can all be used as described above for the monostable.

555/556 Inverting Buffer (Schmitt trigger) or NOT gate

555 inverting buffer circuit
(a NOT gate)

NOT gate symbol

The buffer circuit's input has a very high impedance (about 1M) so it requires only a few µA, but the output can sink or source up to 200mA. This enables a high impedance signal source (such as an LDR) to switch a low impedance output transducer (such as a lamp).
It is an inverting buffer or NOT gate because the output logic state (low/high) is the inverse of the input state:

Input low (< ¹/₃ Vs) makes output high, +Vs
Input high (> ²/₃ Vs) makes output low, 0V

When the input voltage is between ¹/₃ and ²/₃ Vs the output remains in its present state. This intermediate input region is a deadspace where there is no response, a property called hysteresis, it is like backlash in a mechanical linkage. This type of circuit is called a Schmitt trigger. If high sensitivity is required the hysteresis is a problem, but in many circuits it is a helpful property. It gives the input a high immunity to noise because once the circuit output has switched high or low the input must change back by at least ¹/₃ Vs to make the output switch back.

Circuit symbols of electronic components

2008-10-11T17:57:00.002+05:30

Wires and connections
Component	Circuit Symbol	Function of Component
Wire		To pass current very easily from one part of a circuit to another.
Wires joined		A 'blob' should be drawn where wires are connected (joined), but it is sometimes omitted. Wires connected at 'crossroads' should be staggered slightly to form two T-junctions, as shown on the right.
Wires not joined		In complex diagrams it is often necessary to draw wires crossing even though they are not connected. I prefer the 'bridge' symbol shown on the right because the simple crossing on the left may be misread as a join where you have forgotten to add a 'blob'

Power Supplies
Component	Circuit Symbol	Function of Component
Cell		Supplies electrical energy. The larger terminal (on the left) is positive (+). A single cell is often called a battery, but strictly a battery is two or more cells joined together.
Battery		Supplies electrical energy. A battery is more than one cell. The larger terminal (on the left) is positive (+).
DC supply		Supplies electrical energy. DC = Direct Current, always flowing in one direction.
AC supply		Supplies electrical energy. AC = Alternating Current, continually changing direction.
Fuse		A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.
Transformer		Two coils of wire linked by an iron core. Transformers are used to step up (increase) and step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is no electrical connection between the coils.
Earth (Ground)		A connection to earth. For many electronic circuits this is the 0V (zero volts) of the power supply, but for mains electricity and some radio circuits it really means the earth. It is also known as ground.

Resistors
Component	Circuit Symbol	Function of Component
Resistor		A resistor restricts the flow of current, for example to limit the current passing through an LED. A resistor is used with a capacitor in a timing circuit. Some publications still use the old resistor symbol:
Variable Resistor (Rheostat)		This type of variable resistor with 2 contacts (a rheostat) is usually used to control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into a capacitor in a timing circuit.
Variable Resistor (Potentiometer)		This type of variable resistor with 3 contacts (a potentiometer) is usually used to control voltage. It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal.

Capacitors
Component	Circuit Symbol	Function of Component
Capacitor		A capacitor stores electric charge. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.
Capacitor, polarised		A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.
Variable Capacitor		A variable capacitor is used in a radio tuner.
Trimmer Capacitor		This type of variable capacitor (a trimmer) is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment.

Diodes
Component	Circuit Symbol	Function of Component
Diode		A device which only allows current to flow in one direction.
LED Light Emitting Diode		A transducer which converts electrical energy to light.
Zener Diode		A special diode which is used to maintain a fixed voltage across its terminals.
Photodiode		A light-sensitive diode.

Transistors
Component	Circuit Symbol	Function of Component
Transistor NPN		A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.
Transistor PNP		A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.
Phototransistor		A light-sensitive transistor.

Audio and Radio Devices
Component	Circuit Symbol	Function of Component
Microphone		A transducer which converts sound to electrical energy.
Earphone		A transducer which converts electrical energy to sound.
Loudspeaker		A transducer which converts electrical energy to sound.
Piezo Transducer		A transducer which converts electrical energy to sound.
Amplifier (general symbol)		An amplifier circuit with one input. Really it is a block diagram symbol because it represents a circuit rather than just one component.
Aerial (Antenna)		A device which is designed to receive or transmit radio signals. It is also known as an antenna

Logic Gates Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off). There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).
Gate Type	Traditional Symbol	IEC Symbol	Function of Gate
NOT			A NOT gate can only have one input. The 'o' on the output means 'not'. The output of a NOT gate is the inverse (opposite) of its input, so the output is true when the input is false. A NOT gate is also called an inverter.
AND			An AND gate can have two or more inputs. The output of an AND gate is true when all its inputs are true.
NAND			A NAND gate can have two or more inputs. The 'o' on the output means 'not' showing that it is a Not AND gate. The output of a NAND gate is true unless all its inputs are true.
OR			An OR gate can have two or more inputs. The output of an OR gate is true when at least one of its inputs is true.
NOR			A NOR gate can have two or more inputs. The 'o' on the output means 'not' showing that it is a Not OR gate. The output of a NOR gate is true when none of its inputs are true.
EX-OR			An EX-OR gate can only have two inputs. The output of an EX-OR gate is true when its inputs are different (one true, one false).
EX-NOR			An EX-NOR gate can only have two inputs. The 'o' on the output means 'not' showing that it is a Not EX-OR gate. The output of an EX-NOR gate is true when its inputs are the same (both true or both false).

What is web page?

2008-10-03T18:49:00.001+05:30

Browser
A program which allows a person to read hypertext. The browser gives some means of viewing (or listening to) the contents of pages and of navigating from one page to another.
.Com
Generic top-level domain. The most commonly used TLD on the Web.
ccTLD
Country code Top Level Domain. Also referred to as non-US ISO country codes. Some countires register all domains at the top level, e.g. Germany (.de) and Norway, while others create additional structure with Second Level domains (2LDs) such as .co.nz (New Zealand), .co.jp (Japan), .com.tw (Taiwan), et cetera.
.Coop
Restricted top-level domain. Reserved for cooperative businesses.
DNS
A distributed database of information that is used to translate domain names, which are easy for humans to remember and use, into Internet Protocol (IP) numbers, which are what computers need to find each other on the Internet.
People working on computers around the globe maintain their specific portion of this database, and the data held in each portion of the database is made available to all computers and users on the Internet.
The DNS comprises computers, data files, software, and people working together.
Domain Name
In short, a domain name is nothing more than an alias for a numeric web address. Each web site on the internet has a numeric address that functions like coordinates on a map. Instead of pointing to a geographic location on earth, these numeric addresses, called IP addresses, point to a graphical location on the Internet. Computers have no problems with locating and remembering numeric addresses. In contrast, most humans have trouble remembering long, complicated sequences of numbers. So, to make surfing the web easier, the domain name system was invented. This system allows people to use easy to remember names for web sites instead of those number sequences.
.Edu
Generic, restricted top-level domain. Available exclusively to degree-granting educational institutions of higher education that are accredited by one of the six U.S. regional accrediting agencies.
Fully-qualified domain name
A fully-qualified domain name (FQDN) is that portion of an Internet Uniform Resource Locator (URL) that fully identifies the server program that an Internet request is addressed to. The FQDN includes the top-level domain name, the second-level domain name and any other levels. An FQDN should be sufficient to determine a unique Internet address for any host on the Internet. The prefix "http://" added to the fully-qualified domain name completes the URL.
FTP
File Transfer Protocol. The Internet engineering standard for transferring files from one computer to another, i.e. from a web creator's computer files to the virtual server or vice versa. Such a transfer is made via a special FTP software program such as WS_FTP or CuteFTP. There are many Internet sites that have established publicly accessible repositories of material that can be obtained using FTP, by logging in using the account name anonymous, thus these sites are called anonymous ftp servers.
gTLD
Generic Top Level Domain. In the US, gTLDs used to describe organizational and political structures and are usually given three-letter names. Over the past few years, a number of these gTLDs have become "unrestricted", i.e. anyone can register a domain in that gTLD. You do not even have to reside in the US or be a business entity. For domains outside the US, two-letter ISO (International Organization For Standardization) country codes are used. Here are the current gTLDs. Over the next few months, there will likely be new additions to this list: Top level Domain What it used to be for Who can register?
.COM Commercial Companies Anyone - Unrestricted.
.EDU Educational Institutions 4 Year Universities only.
.GOV Government Agcy's Restricted.
.MIL Military Agencies Restricted US Military.
.NET Network Providers Anyone - Unrestricted.
.ORG Not-for-profit organizations Anyone - Unrestricted.
HTML
Documents on the World Wide Web are written in a simple "markup language" called HTML, which stands for HyperText Markup Language. HTML looks a lot like old-fashioned typesetting code, where you surround a block of text with codes that indicate how it should appear, additionally, in HTML you can specify that a block of text, or a word, is linked to another file on the Internet. HTML files are meant to be viewed using a browser, such as Netscape or Internet Explorer.
HTTP
HyperText Transfer Protocol. The protocol for moving hypertext files across the Internet. Requires a HTTP client program on one end, and an HTTP server program on the other end. HTTP is the most important protocol used in the World Wide Web (WWW).
Hypertext
Term coined by Ted Nelson around 1965 for a collection of documents containing cross-references or "links" which, with the aid of an interactive browser program, allow the reader to move easily from one document to another.
IANA
Internet Assigned Numbers Authority The function that currently oversees registration for various Internet Protocol parameters, such as port numbers, protocol and enterprise numbers, options, codes, and types. The IANA function is currently located at the Information Sciences Institute at the University of Southern California in Marina del Rey, CA.
ICANN
Internet Corporation for Assigned Names and Numbers. ICANN is the new non-profit corporation that is assuming responsibility from the U.S. Government for coordinating certain Internet technical functions, including the management of Internet domain name system.
.Info
Generic top-level domain. Unrestricted, but generally used for informative purposes.
InterNIC
http://www.internic.net The InterNIC is a concept for an integrated network information center that was developed by several companies, including Network Solutions, in cooperation with the U.S. Government. Currently, the term "InterNIC" is being used in conjunction with a neutral, stand alone web page (located at: http://www.internic.net/) that is established for the purpose of providing the public with information regarding Internet domain name registration. InterNIC is a registered service mark of the U.S. Department of Commerce.
IP Address
Every machine that is on the Internet has a unique IP number - if a machine does not have an IP number, it is not really on the Internet. Most machines also have one or more domain names that are easier for people to remember.
IP addresses are numerical, often 32-bit addresses that are expressed as four numbers between 0 and 255, separated by periods, for example: 216.168.224.69
For more information, HowStuffWorks.com has an easy to comprehend article on How IP Addresses Work as a part of its larger article on How domain name Servers Work.
ISP (Internet Service Provider)
Internet Service Provider. While rather a generic term, ISP generally refers to a person, organization, or company that allows its users access to the Internet. In addition to Internet access, many ISPs provide other services such as web hosting, DNS and other services.
.Mil
Generic top-level domain operated exclusively by the United States Military.
.Museum
Generic top-level domain reserved for museums.
.Name
Generic top-level domain reserved exclusively for individuals.
Nameserver
Sometimes called a "host." A computer (server) that has both the software and the data (zone files) needed to resolve domain names to Internet Protocol (IP) numbers. Domain names must be programmed into a minimum of two nameservers hosted on separate networks.
.Net
Generic top-level domain. Unrestricted, but primarily used by Internet service providers (ISPs).
NIC
Generally, any office that handles information for a network. The most famous of these on the Internet is the InterNIC, which is where new domain names are registered.
.Org
Generic top-level domain. Unrestricted, but mainly used by nonprofit organizations.
Parking
When a registered domain is parked, the domain is reserved but remains inactive. A temporary Web page is displayed until the site is unparked — or activated. Domain name parking is often used by registrants who do not yet have a hosting provider or who haven't yet built a site for the domain.
.Pro
Soon-to-be-activated generic top-level domain. Once established, the domain will be available exclusively for certified professionals, such as accountants, lawyers and physicians.
Registrant
The individual or organization that registers a specific domain name. This individual or organization holds the right to use that specific domain name for a specified period of time, provided certain conditions are met and the registration (NIC) fees are paid. This person or organization is the "legal entity" bound by the terms of all applicable domain registration Service Agreements.
Registrar
An entity with a direct contractual relationship with, and special access to, a registry, that inserts records on behalf of others.
Registry
A database associating DNS information with some person, legal entity, operational entity, or other reference.
Restricted top-level domain name (rTLD)
A top-level domain, such as .biz, .gov, .museum, .name, and .pro, that is only available to registrants who meet certain criteria.
Root
The top of the domain name System hierarchy. Often referred to as the "dot."
Second-Level Domain
In the domain name System, the next lower level of the hierarchy underneath the top level domains. In a domain name, that portion of the domain name that appears immediately to the left of the top-level domain. For example, the domainsforbeginners in domainsforbeginners.com. Second-Level Domains are the focus of domain speculators and have been the root of a good portion of internet name disputes on the internet. It's important that your second-level domain does not infringe upon the registered trademark of another entity.
Server
A computer, or a software package, that provides a specific kind of service to client software running on other computers. The term can refer to a particular piece of software, such as a WWW server, or to the machine on which the software is running, e.g. Our mail server is down today, that's why e-mail isn't getting out. A single server machine could have several different server software packages running on it, thus providing many different servers to clients on the network.
Technical Contact
The technical contact is the person or organization who maintains the primary domain name server. When you register your domain name with us, we provide our primary nameserver automatically and assume the role of Technical Contact. The technical contact should be able to answer technical questions about the domain name's primary domain name server and work with technically-oriented people in other domains to solve technical problems that affect the domain name.
TLD
Top Level Domain. In the domain name System (DNS), the highest level of the hierarchy after the root. In a domain name, that portion of the domain name that appears furthest to the right. For example, the com in domainsforbeginners.com.
URL
Uniform Resource Locator. An internet "address." A draft standard for specifying the location of an object on the Internet, such as a file or a newsgroup. They are used in HTML documents to specify the target of a hyperlink which is often another HTML document (possibly stored on another computer).
Examples of URLs:
http://www.circuitzone123.blogspot.com
http://www.gatesglobal.com/ The first part of the URL, before the colon (often http), specifies the access method. The part of the URL after the colon is interpreted specific to the access method.
URL Forwarding
URL Redirection or Website Redirection In short, when the user types in one address (URL) for a web site and is then redirected to a site, often on a different server than the domain. Often the URL name entered will be short, easy to remember URL while the destination page is actually defined by a much longer, harder to remember URL. It occurs when a Web server tells the client browser to obtain a certain requested page from a different location. The new URL may be on the same server or a different one and may itself be subject to redirection. The user is normally unaware of this process except that it may introduce extra delay while the browser sends the new request and the browser will usually (although not always) display the new URL rather than the one the user originally requested.
.Us
Country-code top-level domain. Available exclusively for residents of the United States and its territories.
Virtual host
Also called an IPP. In order to establish a full-time presence on the internet, one needs to have computers that are connected continuously to the Internet. Special hardware and software are needed as well as constant maintenance of a full-time high speed connection to the internet. A virtual host provides services to relieve its hosted customers from the burden of dedicating costly hardware/software and valuable human resources to its web presence effort. Because the electronic frontage (or website) actually resides on the IPP's computers, and not that of the entity, it's virtual. This is where the name "virtual host" comes from.
Web Page
Simply, a block of information running on a web server identified by a specific URL. Such pages are most often written in HTML. It is also possible for a server to create a dynamic web page via special scripts.
Web Site
Simply put, a block of information running on a web server. A web site may or may not of a group of pages related to one another, and is identified by its Second-Level Domain.
WhoIs
A searchable database maintained by the registrar, which contains information about networks, networking organizations, domain names, and the contacts associated with them for respective domains. Also, the set of rules that describes the application used to access the database.
.Ws
The Country-Code Top Level Domain for Western Samoa, but marketed for general use with the suggestion that it stands for "web site".

What is a URL?

2008-10-03T18:29:00.001+05:30

A URL is the location of a file on the Web. Some examples of URLs include http://www.blogger.com/, or http://myblog.blogspot.com/. The URL you select will be used by visitors, or yourself, to access your blog.
During the blog creation process you'll have to select a URL for your blog if you want it hosted on Blog*Spot. Since there are already a large number of Blog*Spot blogs, you'll need to get creative and possibly try a few different ones before you find one that's available.
One thing to note when selecting your blog's URL is that hyphens (also know as dashes, - ) are the only non-alphanumeric characters allowed. Spaces aren't permitted, nor are underscores (_) or any other special characters.

Now control ur PC With TV Remote

2008-10-01T17:36:00.000+05:30

Now you can control your mouse cursor and windows media player with your TV remote... So when you are watching a movie or listening songs on your PC, you need not to get up from your seat to change the volume or to change the track.. you can simply use your TV remote to do this.Description:
This project is an implementation of RC5-remote reception on an 8051 microcontroller. The received code is decoded and sent to the PC IR remote software written in Visual Basic. The cursor position is moved according to the keys pressed.
There are two modes of operation one is as mouse control and second is Windows media player control. More information on key control is given in the software's help section. You might need to download the VB library files to run this software.
If the software gives an error of missing file "MSCOMM32.ocx", the use the ocx file supplied in the zip file and follow the instructions below:

Copy MSCOMM32.ocx in "c:\windows\system" folder.
Go to Start -> run and type "regsvr32 mscomm32.ocx" and hit enter. It will give you a success dialog.

2 Transistor FM Voice Transmitter

2008-10-01T17:32:00.000+05:30

Take care with transmitter circuits. Although only low power this circuit may be tuned to operate over the range 87-108MHz with a range of 20 or 30 metres .I have used a pair of BC548 transistors in this circuit. Although not strictly RF transistors, they still give good results. I have used an ECM Mic insert from Maplin Electronics, order code FS43W. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor. The coil L1 was again from Maplin, part no. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter. Actual range on my prototype tuned from 70MHz to around 120MHz. The aerial is a few inches of wire. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work. Although RF circuits are best constructed on a PCB, you can get away with veroboard , all leads short, and break tracks at appropriate points.

One final point, don't hold the circuit in your hand and try to speak. Body capacitance is equivalent to a 200pF capacitor shunted to earth, damping all oscillations. I have had some first hand experience of this problem. The frequency of oscillation can be found from the theory

How Do Transistors Work?

2008-09-30T19:21:00.000+05:30

To turn on an NPN transistor, a voltage is applied across the base and emitter terminals. This causes electrons in the Base wire to move away from the transistor itself and flow out towards the power supply. This in turn pulls electrons out of the P-type base region, leaving 'holes' behind, and the 'holes' act like positive charges which are pushed in the opposite direction from the direction of electron current. What SEEMS to happen is that the base wire injects positive charges into the base region. It spews holes. It injects charge.

(Note that I'm describing charge flow here, not positive-charge "conventional current.")

              
       ____________
                  
       COLLECTOR N
      _____________                  ELECTRONS ARE PULLED FROM THE
                     ----->          BASE REGION AND INTO THE WIRE,
       BASE      P ______________    WHICH CREATES POSITIVE "HOLES"
      _____________                +  WHICH SPEW OUT INTO THE BASE
                             ________   REGION.
       EMITTER  N              _____
      _____________          _________
                                _____
             _____________________  -

That's part of the conventional explanation. Why is all of this important to transistor operation? ***It's not!*** The base current is not important to transistor operation. It's just a byproduct of the REAL operation, which involves an insulating layer called the Depletion Region. By concentrating on the current in the Base lead, most authors go up a dead end in their explanations. To avoid this fate, we must start out ignoring the base current. Instead we look elsewhere for understanding. See the diagram below.

              
       ____________
                           \
       COLLECTOR          
                            > full of wandering electrons
        n-doped                        
      _____________        /             
                               \ 
       BASE                     
                   --           > full of wandering "holes"
        p-doped                 
      _____________            /
                         \    
       EMITTER              
                          > full of wandering electrons   
        n-doped         
      _____________      /

The Depletion Region is an insulating layer existing between the base region and the emitter region. Why is it there? It exists because the Base region is p-doped silicon; it exists because p-type silicon is full of naturally-occurring movable "holes," and because the p-type silicon is touching n-type silicon.

              
       ____________
                  
       COLLECTOR N
      _____________                    
                                
       BASE      P --
      _____________        
       _____________   <-- insulating "depletion layer"

                       
      EMITTER  N 
      ___________

Electrons in p-type silicon act like the closely-packed beads of an abacus, and the "holes" are like gaps in the rows of beads. Move one bead, and a hole has moved the other way. Touch the p-type silicon against the n-type, and wandering electrons from the n-type silicon will fall into the holes. Also, holes in the p-type's Base region flow out among the movable electrons from the N-type Emitter region and many are cancelled. Holes swallow electrons, and this leaves a thin region between N and P sections which lacks movable charges.

Remember: a conductor is not a substance which allows charges to pass. (Don't forget #3 above!) Actually a conductor is any substance which contains charges which are movable. Anything that lacks movable charges is an insulator. Inside the depletion layer, all the opposite charges have fallen together and vanished. The gaps in the abacus beads are gone, so no beads can move anymore. Lacking mobile charges, the silicon has turned into an insulator. When there's no voltage applied across the base/emitter terminals, this insulating layer grows fairly thick, and the transistor acts like a switch which has been turned off.

I like to visualize that a transistor's silicon is normally like a shiny silver conductor (sort of like metal) ...except for this insulating layer between the P and N regions which acts more like a layer of insulating glass. Silicon is like a metal which can become glass!

              
       ____________
                           \
       COLLECTOR N        
      _____________         >  Shiny silver conductive     
                          
       BASE      P --      /
      _____________           
       _____________    <-- Glasslike insulating "depletion layer"                                      \         EMITTER  N             >  Shiny silver conductive
      _____________          /

When voltage is applied between base and emitter, this insulating layer changes thickness. If (+)voltage is applied to the p-type, to the base wire, while a (-) voltage polarity is applied to the n-type, to the emitter wire, then electrons in the n-type are pushed towards the holes in the p-type. The insulating layer becomes so thin that the clouds of electrons and holes start meeting and combining. A current therefore exists in the base/emitter circuit. But this current is not important to transistor action. What's important to notice is that the *VOLTAGE* across the base/emitter has caused the insulating Depletion Layer to become so thin that the charges can now flow across it. It's as if the transistor contains a layer of glass whose thickness can be varied when we alter a voltage. The layer becomes thinner when base/emitter voltage is increased. This happens because the voltage pushes the holes and the electrons towards each other, reducing the size of the empty insulating region between the clouds of holes and electrons, and allowing the stragglers to jump across the insulator. The depletion layer is a voltage-controlled switch which "closes" when the right polarity of voltage is applied. It is also a proportional switch, since a small voltage can close it only partially. For silicon material, charges start jumping across when the voltage is around 0.3V. Raise the voltage to 0.7V and the current gets very high. (That's for silicon. Other materials have different turn-on voltages.) The larger the voltage, the thinner the insulating layer, so the higher the current in the entire transistor. By applying the right voltage, we can thicken or thin the depletion layer as desired, creating an open, closed, or partially open switch.

Handy Zener Diode Tester

2008-09-30T19:19:00.000+05:30

Here is a handy zener diode tester which tests zener diodes with breakdown voltages extending up to 120 volts. The main advantage of this circuit is that it works with a voltage as low as 6V DC and consumes less than 8 mA current. The circuit can be fitted in a 9V battery box. Two-third of the box may be used for four 1.5V batteries and the remaining one-third is sufficient for accommodating this circuit. In this circuit a commonly available transformer with 230V AC primary to 9-0-9V, 500mA secondary is used in reverse to achieve higher AC voltage across 230V AC terminals. Transistor T1 (BC547) is configured as an oscillator and driver to obtain required AC voltage across transformer’s 230V AC terminals. This AC voltage is converted to DC by diode D1 and filter capacitor C2 and is used to test the zener diodes. R3 is used as a seri- es current limiting resistor. After assembling the circuit, check DC voltage across points A and B without connecting any zener diode. Now switch on S1. The DC voltage across A-B should vary from 10V to 120V by adjusting potmeter VR1 (10k). If every thing is all right, the circuit is ready for use. For testing a zener diode of unknown value, connect it across points A and B with cathode towards A. Adjust potmeter VR1 so as to obtain the maximum DC voltage across A and B. Note down this zener value corresponding to DC voltage reading on the digital multimeter. When testing zener diode of value less than 3.3V, the meter shows less voltage instead of the actual zener value. However, correct reading is obtained for zener diodes of value above 5.8V with a tolerance of ± 10per cent. In case zener diode shorts, the multimeter shows 0 volts

Digital volume control

2008-09-30T19:16:00.000+05:30

Circuit of a digital volume control using six discrete ICs, including a 5V regulator, is presented. IC1 (555) is configured to function as astable flip-flop. Its frequency or period may be adjusted by proper choice of resistors R44, R45 and capacitor C6 combination. Here it is for 0.3 second period. IC2 is a presetable up/down counter. In this circuit up-mode is used for increasing and down-mode is used for decreasing the volume. IC3 and IC4 are 16-channel analogue multiplexers which function as analogue switches. Here IC3 is used as level indicator while IC4 is used as a potentiometer. Soon after the power is switched on, switch S1 is to be pressed to reset the whole system. When switch S2 is pressed, IC2 counts up the number of pulses and the result is available in the form of BCD output. IC6 is used as an interface between TTL and CMOS ICs. The BCD output controls the address input lines of IC2 and IC3, and selects/switches one, out of sixteen channels, by turning on the appropriate analogue switch. In the circuit, IC4 is used as a potentiometer by connecting 15 resistors (R9 through R23) between each of its 16 input pins and a resistor/capacitor combination of C2, C3 and R7 at its output. The values of resistors R9 through R23 can, of course, be selected as desired. Here the resistors have been selected for a logarithmic scale. Switch S2 is used for increasing and switch S3 is used for decreasing the volume. Similarly, switches S4 and S5 are provided for second channel (right channel) volume control. Also, pin 14 of IC2 can be connected to IC 74193 pin 14 (clear input) of the right channel volume control circuit. The volume control circuit of right channel will be identical to that of the left channel circuit (shown here) except that IC1, IC5 and push-to-on switches are not to be duplicated. A 1µF electrolytic capacitor (C4) is used to prevent switching noise. Resistors R8 and R6 are used to fix the quiescent operating voltage level at half the supply voltage for avoiding distortion of the audio signal from the preamplifier. Capacitors C2, C3 and resistor R7 are provided for proper filtering of the audio and blocking DC component. An exact logarithmic scale of resistors R9 through R23 produces a pleasing and smooth control.

Electronic scoring Circuit

2008-09-30T19:13:00.000+05:30

You can play this game alone or with your friends. The circuit comprises a timer IC, two decade counters and a display driver along with a 7-segment display. The game is simple. As stated above, it is a scoring game and the competitor who scores 100 points rapidly (in short steps) is the winner. For scoring, one has the option of pressing either switch S2 or S3. Switch S2, when pressed, makes the counter count in the forward direction, while switch S3 helps to count downwards. Before starting a fresh game, and for that matter even a fresh move, you must press switch S1 to reset the circuit. Thereafter, press any of the two switches, i.e. S2 or S3. On pressing switch S2 or S3, the counter’s BCD outputs change very rapidly and when you release the switch, the last number remains latched at the output of IC2. The latched BCD number is input to BCD to 7-segment decoder/driver IC3 which drives a common-anode display DIS1. However, you can read this number only when you press switch S4. The sequence of operations for playing the game between, say two players ‘X’ and ‘Y’, is summarised below:

1. Player ‘X’ starts by momentary pressing of reset switch S1 followed by pressing and releasing of either switch S2 or S3. Thereafter he presses switch S4 to read the display (score) and notes down this number (say X1) manually.
2. Player ‘Y’ also starts by momentary pressing of switch S1 followed by pressing of switch S2 or S3 and then notes down his score (say Y1), after pressing switch S4, exactly in the same fashion as done by the first player.
3. Player ‘X’ again presses switch S1 and repeats the steps shown in step 1 above and notes down his new score (say, X2). He adds up this score to his previous score. The same procedure is repeated by player ‘Y’ in his turn.
4. The game carries on until the score attained by one of the two players totals up to or exceeds 100, to be declared as the winner.
Several players can participate in this game, with each getting a chance to score during his own turn. The assembly can be done using a multipurpose board. Fix the display (LEDs and 7-segment display) on top of the cabinet along with the three switches. The supply voltage for the circuit is 5V.