Computer keyboards
by Chris Woodford. Last updated: February 26, 2022.
Tap tap tap! Tap tap tap!
That's the sound of someone thinking aloud in the 21st century, which
typically means banging out words in a blog or an email or
word-processing an essay or a forum post.
Computer keyboards are generally quicker to use than old-fashioned
typewriter keyboards,
though they're still no match for dictating your documents with voice recognition software.
Have you ever stopped to wonder what your keyboard's like inside?
You might be surprised to find it's just a load of electrical switches.
Let's take a closer look!
Photo: A typical low-cost computer keyboard.
Each key is nothing more than a switch: it closes an electrical circuit
when you
press it down and opens the circuit when you release it again.
A word of warning!
You've heard me say this before. Taking things to bits is a brilliant
way
to learn how they work but, for a whole bunch of reasons, it's often
dangerous, difficult, or ill-advised. In the case of computer keyboards, there's
not a lot of danger,
but there are a couple of hundred tiny pieces that fall out very
easily.
If you drop the keyboard while you're messing about with it, expect to
find yourself taking at least a couple of hours to put it all
back together again. You have been warned!
What's under the keys?
Pull a key off the keyboard and you can see roughly how it works.
There's a little hole in the plastic base and the keyboard has a long
round bar the same shape. When you press the key, the bar pushes down
through the hole to touch the contact layers below.
Inside the hole, there's a little tiny piece of rubber (you can't see
it in this photo) that stops the key moving down and pushes it back up
when you release it. This is what gives the spring to the keys.
What's under the keyboard?
Take off the keyboard's bottom panel and you can see how it all
works from beneath. You can see the transparent plastic contact layers
that detect key presses and (through those layers) you can see the round
bars poking the keys down from above. The green rectangle at the top
contains three small LEDs that activate the
indicator lights for "Num lock", "Caps lock", and "Scroll lock".
Notice also the cable running along the inside of the case at the top of the keyboard,
which carries electrical signals from the keyboard to your computer's
USB port (or PS/2 port on older machines).
How do the keys press down?
Peel back the electrical contact layers and you can see the bottom
of the keys and where they press down. Balancing on my fingertip, you
can see one of the little rubber pieces that makes the keys bounce up
and down. Notice the pattern of electrical tracks on the contact
layers. In this photo, we are looking down through the bottom of the keyboard
(so the keys are underneath).
How do the contact layers work?
This is the magic part of a keyboard. There are three separate
layers of plastic that work together to detect your key presses. Two of
them are covered in electrically conducting metal tracks and there's an
insulating layer between them with holes in it. The dots you can see
are places where the keys press the two conducting layers together. The
lines are electrical connections that allow tiny electric currents to
flow when the layers are pressed tight to one another by a key moving
down from above.
In the photo below, you can see a closeup of the underside of one key—and, if you look closely, just about see how it works. There's one set of electrical connections on the lower sheet of plastic, printed in light gray. The other set is on the upper sheet
of plastic and printed in dark gray. The two sheets are kept apart by a clear plastic layer except at the holes, which
is where the keys push down to make the two sheets touch.
How does it all work together?
When you press a key, the top and bottom contact layers come together and the keyboard sends a signal to your computer—just like this...
Are laptops the same?
Laptops have much shallower keyboards because they have to close up tightly. That means the keys are much thinner and, if you pop them off, you'll notice they're often attached in a different way. On this Toshiba keyboard, there's no long bar on the back of the keys. Instead, each key is essentially flat with four little holes on the back that snap onto the four white plastic pegs you see here, holding it in place but allowing it to move up and down. The blue thing in the middle is the "spring" that pushes the key
back up when you release it. Underneath all this, the contact layer mechanism is essentially the same.
How do keypads work?
TV remote controls, cellphones, push-button telephones, and all kinds of other little gadgets use a different kind of key-switch mechanism that's simpler, more compact, and cheaper to make: it's called a rubber-membrane keypad.
Instead of plastic keys and contact layers, there are just two parts. On top, there's the keypad part with all the keys molded from a single
piece of flexible (rubbery) plastic. The underside of each key is coated with a small
patch of electrically conducting material. The second part of the keypad is a layer of electrical contacts formed directly onto a circuit board. When you press down on a key, the conducting material bridges the contacts, completes a switch, and triggers the specific circuit for that key. The problem with keypads like this is that you get oily films or dirt building up between the two layers, which can stop one or more keys from working. They also feel very "squidgy" to the touch, which makes them unsuitable for ordinary computer keyboards.
Photo: Above and below: A typical TV remote control is made from two layers. In this photo, I've taken them apart and placed them side by side. Left: The main circuit board (green) has patterns of electrical contacts on its surface that sit directly underneath the rubber keys. Right: The rubber membrane keypad (white) is made from a very flexible plastic. When you squash a key down with your finger, you push the electrically conducting contact on the base of the key onto the tracks on the circuit board underneath, closing a switch and activating that key. Below: The components in the keypad laid out side by side.
How to make your laptop keyboard last longer
Photo: Using a laptop with an external keyboard. This is a compact keyboard without a numeric keypad so it takes up much less room than a full-sized keyboard. Sometimes an arrangement like this is uncomfortable because it puts the screen too far from your eyes to see. If you have that problem, prop your laptop on a box or buy a stand (search online for "laptop stand" or "laptop riser").
If you write a lot—like I do—and you use a laptop as your main computer,
don't be at all surprised if you wear out the keyboard. How can you wear out a keyboard?
Easily! Let's say you write 1000 words a day (a fairly high output for a writer, but not unusual),
so you're pressing as many as 50–100,000 keys a week! Clattering away at that rate, it won't take you more than a few years to clock up a few million key presses—which is roughly the life expectancy of a basic keyboard.
Laptop keyboards are much more flimsy than desktop keyboards: they're designed for casual home use, not constant, industrial-strength pounding. Why do the keys wear out? Each time you press, you squeeze the contact layers together. Sooner or later,
you'll find some keys that stick down permanently (as though they're on auto-repeat), even when you're not pressing, because the layers
refuse to spring apart again (or sometimes get dirt trapped in them). I know from experience that having a new keyboard fitted to a laptop can be extremely expensive: with labor charges, it can cost up to a third as much as a new machine. I had to
wear out the keyboard twice on one of my laptops before I learned my lesson.
And what is the lesson? If you do lots of typing, it will pay you to buy an inexpensive
plug-in USB (or wireless Bluetooth) keyboard and use your laptop propped up on a stand (or a box). An external keyboard can cost as little as $10 (£5 or so). Buy one with a new laptop and use it routinely and you'll save a fortune on keyboard repairs. As an added benefit, a plug-in keyboard may also feel more comfortable and allow you to type faster, and, if it's set up properly, it could reduce the chance of your developing medical problems like RSI (repetitive strain injury).
Who invented modern computer keyboards?
Artwork: The original circuit-based computer keyboard? James Martin Comstock's 1969 design has an upper layer of keys (light blue) on springs (yellow), a moving metal contact layer (green, orange, and red), and a circuit board (dark blue) with connection points (yellow), just like a modern keyboard. From US Patent 3,591,749: Printed circuit keyboard, courtesy of US Patent and Trademark Office.
With their strange "QWERTYUIOP" sequence of keys, modern computer keyboards clearly evolved from late-19th-century manual typewriters. Instead of keys mounted on a circuit board, those mechanical monsters used an intricate system of levers and springs to bang noisy metal hammers against a sheet of paper.
As electric and electronic were developed, the number of moving parts gradually diminished, yet it's quite hard to settle on any one person or keyboard that made the decisive switch from mechanical keyboard to electronic one. I've looked through invention records and the earliest description I can find of a modern keyboard like the one I've described in this article is
US Patent 3,591,749: Printed circuit keyboard by James Martin Comstock of The Singer Company, filed in 1969 and granted in 1971. As Martin explained in his patent, the advantages are obvious: it's cheap to build, has few moving parts to go wrong, and it's easy to connect to other equipment (making it very simple to replace if it ever does fail).
Find out more
On this site
Some other articles on our site you might enjoy:
On other sites
News articles
- France Plans a New Keyboard to Shift Control to Typists by Aurelien Breeden. The New York Times. January 22, 2016. The Azerty keyboard makes it easier to type accented characters, but something simpler is needed, argues the French government.
- Why I use a 20-year-old IBM Model M keyboard by Iljitsch van Beijnum. Ars Technica, November 2013. A retro-keyboard enthusiast explains the attractions of older technology.
- How to Replace Your Laptop Keyboard by Eric Geier, PCWorld, July 12, 2012. A handy, practical guide to relacing a broken or sticky keyboard in a laptop.
- Beyond the keyboard and mouse by Chris Vallance, BBC News, March 14, 2008. What other forms of computer input will we use in future?
Other articles
- So Many Gadgets, So Many Aches by Phyllis Korkki. The New York Times, September 10, 2011. From laptops to smartphones, mobile computing is taking a growing toll on our bodies.
Patents
- US Patent 6,547,463B1: Collapsible keyboard by Jyh-Yi Loo, Changshu Sunrex. April 15, 2003. An example of a folding keyboard mechanism.
- US Patent 4,639,559A: Membrane keyboard by Toshimichi Taguchi, Sharp Corporation. January 27, 1987. A simple membrane-type keyboard with laminated conducting sheets.
- US Patent US4,274,752A: Keyboard multiple switch assembly by Daniel Huber et al, IBM. June 23, 1981. A more complex mechanical keyboard switch that can do different things if you press it in different ways.
- US Patent 3,591,749: Printed circuit keyboard by James Martin Comstock, Singer Company. July 6, 1971. The basic numeric keypad illustrated up above.
- US Patent 559,756: Type-writing machine by Christopher Latham Sholes. May 5, 1896. An early Sholes patent illustrates the connection between old typewriters and modern keyboards.
