Dome-switch keyboards are kind of a hybrid of membrane and mechanical keyboards.
They bring two circuit board traces together under a rubber "dome" or bubble.
The inside of the top of the bubble is coated in some conductive substance. When
a key is pressed, it collapses the dome, which shorts out the two circuit traces
and completes the connection to enter the character. The pattern on the PC board
is often gold-plated.
This is a common switch technology used in mass market keyboards today. It is
considered very quiet, but purists tend to find it "mushy" because the collapsing
dome does not provide as much positive response as a hard closing switch. These
are also a good choice for office or consumer environments because they are generally
fairly quiet. This switch technology also happens to be most commonly used in handheld
controllers, such as those used with home video game consoles.
Dome-switch keyboards are also called direct-switch keyboards.
In this type of keyboard, pressing the key changes the capacitance of a pattern
printed on a PC board. Usually this permits a pulse or pulse train to be sensed.
Unlike "dome switch" keyboards, the pattern will be covered by a thin, insulating
film. Capacitive keyboards are inexpensive, and resist wear, water, foreign objects
and dirt. They are common in PC keyboards.
Mechanical-switch keyboards use real switches, one under each key. Depending
on the construction of the switch, these keyboards have varying responses and travel
times. Notable keyboards utilizing this technology are the Apple Extended II, and
its modern imitator, the Matias Tactile Pro. These two keyboards use ALPS
switches. Cherry Corporation of Germany also makes mechanical switches used
in special purpose and high end keyboards. In India, the TVS Gold mechanical
keyboard is very popular in spite of the fact that it costs about five times what
a membrane keyboard costs. The Matias Tactile Pro is a decent approximation of the
Apple Extended II keyboard, however the grade of the plastic is noticeably cheaper.
Its construction , besides having decent quality key-switches, is less than par,
with flimsy keyboard risers on the bottom of the keyboard and USB ports that are
too tight. Although the keyboard has these quality flaws, it`s still better than
most available keyboards today, except probably the IBM Model M replacements.
It is a common misconception that the IBM Model M and its derivates are mechanical-switch
keyboards. In fact, the Model M uses membrane-sheet switches, much like those found
in a dome-switch keyboard. The buckling spring mechanism ( U.S. Patent 4,118,611
) atop the switch is responsible for the tactile and aural response of
the keyboard. This mechanism controls a small hammer that strikes the membrane switch.
For more information, see an examination of buckling-spring technology.
In 1993, two years after spawning Lexmark, IBM transferred its keyboard
operations to the daughter company. New Model M keyboards continued to be manufactured
for IBM by Lexmark until 1996, when Unicomp purchased the keyboard technology.
Today, Unicomp manufactures new buckling-spring keyboards and repairs old IBM and
Lexmark keyboards. Unfortunately, the later Lexmark-manufactured Model M keyboards
are of inferior quality to the original IBM-manufactured Model M. The plastic used
is of lower grade (density) and other features such as a detachable heavy duty keyboard
cord were replaced by cheap substitutes.
Hall effect keyboards use magnets and Hall effect sensors instead
of an actual switch. When a key is depressed, it moves a magnet, which is detected
by the solid-state sensor. These keyboards are extremely reliable, and are able
to accept millions of keystrokes before failing. They are used for ultra-high reliability
applications, in locations like nuclear powerplants or aircraft cockpits. They are
also sometimes used in industrial environments. These keyboards can be easily made
totally waterproof. They also resist large amounts of dust and contaminants. Because
a magnet and sensor is required for each key, as well as custom control electronics,
they are very expensive.
A laser projection device approximately the size of a computer mouse projects
the outline of keyboard keys onto a flat surface, such as a table or desk. When
the laser is interrupted in the position of a key, a keystroke is registered. This
type of keyboard is very portable, and many models have retractable cords and wireless
capabilities. However, sudden or accidental disruption of the laser will register
unwanted keystrokes. Also, if the laser malfunctions, the whole unit becomes useless,
unlike conventional keyboards which can be used even if a variety of parts (such
as the keycaps) are removed. This type of keyboard can be cumbersome to use since
it is susceptible to errors, even in the course of normal typing, and its complete
lack of tactile feedback makes it even less user-friendly than the cheapest membrane
- Main article: Membrane keyboard
Membrane keyboards are usually flat. They are most often found on appliances
like microwave ovens or photocopiers. A common design consists of three
layers. The top layer (and the one the user touches) has the labels printed on its
front and conductive stripes printed on the back. Under this it has a spacer layer,
which holds the front and back layer apart so that they do not normally make electrical
contact. The back layer has conductive stripes printed perpendicularly to those
of the front layer.
When placed together, the stripes form a grid. When the user pushes down at a
particular position, his finger pushes the front layer down through the spacer layer
to close a circuit at one of the intersections of the grid. This indicates to the
computer or keyboard control processor that a particular button has been pressed.
Membrane keyboards do not generally have much of a "feel", so many machines which
use them issue a beep or flash a light when the key is pressed. They are often used
in harsh environments where water or leak proofing is desirable. Although used in
the early days of the personal computer (on the ZX80, ZX81 and Atari
400), they have been supplanted by the more tactile dome and mechanical switch
keyboards. However, membrane keyboards with interchangeable key layouts, such as
the IntelliKeys and Discover:board are still commonly used by people with
physical, visual, or cognitive disabilities as well as people who require
assistive technology to access a computer.
Some keyboards are designed out of flexible materials that can roll up in a tight
(but not too tight) bundle. Normally the external materials are either silicone
or PU. It is important to note that although many manufacturers claim that the keyboards
are foldable, they cannot be folded without damaging the membrane that holds the
Typically they are completely sealed in rubber, making them watertight like membrane
keyboards. Like membrane keyboards, they are reported to be very hard to get used
to, as there is little tactile feedback.
See Roll-away computer.
Waterproof keyboards are designed to prevent the ingress of water from interfering
with operation. Membrane keyboards are inherently waterproof due to their absence
of areas in which water can enter. Other designs consist of sliding contacts or
flexible rubber seals between the deck plate openings and the key stems.
Other parts of PC keyboard
The modern PC keyboard is more than just the switch technology, however. It also
includes a control processor and indicator lights to provide feedback to the user
about what state the keyboard is in. Depending on the sophistication of the controller`s
programming, the keyboard may also offer other special features.
The processor is usually a single chip 8048 microcontroller variant.
The keyboard switch matrix is wired to its inputs and it processes the incoming
keystrokes and sends the results down a serial cable (the keyboard cord) to a receiver
in the main computer box. It also controls the illumination of the " caps lock",
" num lock" and " scroll lock" lights.
A common test for whether the computer has crashed is pressing the "caps lock"
key. The keyboard sends the key code to the BIOS code running in the main computer;
if the main computer is operating, it commands the light to turn on. All the other
indicator lights work in a similar way. The BIOS also tracks the shift, alt
and control state of the keyboard.
When pressing a keyboard key, the key "bounces" like a ball against its contacts
several times before it settles into firm contact. When released, it bounces some
more until it reverts to the uncontacted state. If the computer was watching for
each pulse, it would see many keystrokes for what the user thought was just one.
To resolve this problem, the processor in a keyboard (or computer) "debounces"
the keystrokes, by aggregating them across time to produce one "confirmed" keystroke
that (usually) corresponds to what is typically a solid contact. It could be argued
that the dome switch technology outlined above owes its popularity to the ability
of the processor to accurately debounce the keystrokes. Early membrane keyboards
limited typing speed because they had to do significant debouncing. Anyone who ever
tried word processing on a ZX81 will recall this.
Retrieved from "http://en.wikipedia.org/wiki/Keyboard_technology"
Category: Computer keyboards
- Taking apart a dome-switch keyboard
Article Discussion Edit this page History
Main Page Community Portal Featured content Current
events Recent changes Random article Help
Beware of Spyware - By Nowshade Kabir
One day, you suddenly realize that your computer started to work noticeably
slower than it used to. You decide to run de-fragmentation of your hard drive and
add more virtual memory to the system. No luck! May be, it?s probably some viruses,
you reckon turning on your virus scanning software. Even after running the anti-virus
program you notice that the problem won?t resolve. Not understanding what?s happening
frustrated you pick up the phone. It?s time to call your tech-support. Sounds familiar?
You are not alone! Each day, thousands of users are facing similar problems caused
by malicious software called Spyware. According to Dell technical support, nowadays
12 percent of their support calls involve problems related to some kinds of Spyware.
Microsoft reports that fifty percent of all computer crushes are caused by Spyware,
viruses and Trojans.
What is a Spyware?
Spyware ? also named Malware or Adware ? are malicious software programs, which
most of the time get installed on your computer without your knowledge. These programs
are capable of doing many outrageous, sinister things to your computer such as changing
computer settings, tracking your online behavior, monitoring and controlling your
computer, recording your keystrokes, displaying unwanted advertisement and reporting
needed information back to the person behind it.
The main types of Spyware are:
Key loggers: This type of Spyware copies everything you type to a file and send
it to the hacker. The more sophisticated type, which is used for identity theft,
copies the information you provide when you are connected to a secure website.
Browser hijacker: It modifies browser settings without your permission. This
Spyware is capable of changing your start page, search page, search tool bar and
redirect your url to specific pages.
Email redirector: Surreptitiously copies all your incoming and outgoing emails
and sends to the hacker.
Dialers: This spyware install themselves to your dial-up settings and dials numbers
without your knowledge, often to out of country numbers.
Collectware: The purpose of this Spyware is to track your surfing habit and transmitting
the statistical data to the hacker. This information later gets sold to advertisement
Adware: This Spyware downloads all sorts of banner advertisements every time
you take some action such as typing a word on your search tool.
Why my antivirus program does not block a Spyware?
Although, Spyware uses same tactics like ?Trojan? virus, technically it is not
a virus. A virus is a program written to create trouble or possibly harm your computer
system. Viruses are capable of replicate, evolve and cause severe damages to your
computer files, registry or even hardware. Spyware, on the other hand, does not
harm your computer intentionally. Any nuisance like system slow down is the collateral
damage, which occurs while the Spyware serves its mission of monitoring your activities
and making unwanted changes to your user experience.
People rarely read the fine prints of the user agreements while downloading a
file, a program, a game or other free stuffs from the Internet. Unethical sites
use this to their advantage and add tiny Spyware with the file you are downloading.
The anti-virus programs can not be sure, whether this program is installed deliberately
by you or it?s a malicious Spyware. This makes identifying and blocking a Spyware
difficult for an Anti-virus program. However, things are started to change! Major
anti-virus companies are planning to integrate anti-spyware programs to their existing
products very soon.
How did I get infected with a Spyware?
There are numerous ways how you might end up with having a Spyware on your system.
- When you download and install programs, games, smilies, pictures, screensavers
from dubious sites, there is a big chance that you might install a sneaky Spyware
along the way.
- Some websites and pop-up windows try to download and install Spyware while
you are there. According a recent analysis of sex-based websites, up to 80 percent
of these sites are now being used to upload Spyware, worms and Trojans to unsuspecting
- Some add-ons to you browser that is supposed to enhance your browser experience
may secretively install Spyware.
- The most cynical method of infecting you with Spyware is when you receive a
sudden pop-up ad, which claims that your computer is contaminated and you have to
run certain program to cure your system. If you are credulous enough to run this
program, it just installs a Spyware instead of eliminating any.
How to fight back?
If you carefully follow the instructions outlined below, your chances of getting
infected with Spyware are pretty slim.
Update your Windows
Allow your version of Windows to update it automatically. Ensure that you have
all the latest security patches installed.
Use Firefox as your default browser
Since Internet Explorer is the main target for many Spyware, you will be better
of with Mozilla Firefox. Moreover, it is a better browser than IE in many aspects.
Be extremely careful with your downloads
Try not to download anything from a unknown site. If you still feel like getting
a shareware or freeware program check it out on one of these online Spyware database.
Spychecker (http://www.spychecker.com/) is one such service, and Camtech 2000`s
Spy Chaser (http://camtech2000.net/Pages/SpyChaser.html) is a nifty downloadable
database of nearly 1000 spyware-infested programs.
Use an Anti-Spyware application
Download and install one of the following anti-spyware programs:
Ad-aware (http://www.lavasoftusa.com/software/adaware/), Spybot (http://www.safer-networking.org/en/spybotsd/index.html)
and Microsoft AntiSpyware. Although, Microsoft?s Anti-Spyware
(http://www.microsoft.com/athome/security/spyware/software/default.mspx) is still
at beta stage, I am using it and very happy with its performance.
Get a Firewall
If you are using Windows XP with Service Pack 2, you are probably fine! In other
cases, if your computer is connected to the Internet directly you should get a firewall
and install it. Zone alarm
(http://www.zonelabs.com/store/content/home.jsp) is a great firewall you can
download for free.
A recently conducted survey of the Top Network Security threats in 2005 reveals
that two-thirds of IT managers and administrators believe that Spyware will be the
number one threat to network security. So don?t take any chance! Make sure that
you are protected!
Nowshade Kabir is the founder,
primary developer and present CEO of Rusbiz.com. A Ph. D. in Information Technology,
he has wide experience in Business Consulting, International Trade and Web Marketing.
Rusbiz is a Global B2B Emarketplace with solutions to start and run online business.
You can contact him at mailto:nowshade[at]rusbiz.com
Typing articles index