Computer Questions: How Computer Keyboards Work

Anyone that owns a computer has used a keyboard. However, few know how they really work.

Anyone that owns a computer has used a keyboard. Thousands of people use them everyday. However, few know how keyboards really work. A typical keyboard is actually a computer in itself!

Basically, a keyboard is an arrangement of switches (keys) connected to a microprocessor. Understanding a microprocessor can be confusing. Technologically, it is a circuit chip that enacts several processings and controls in a system. In its essence, a microprocessor is the central processing component in a computer. It monitors the condition of each key and produces a specific function when the condition changes.

There are several different types of keyboards. Since their invention, new keys have been added to keyboards so that they can perform additional functions. The most conventional keyboards are the 82-key Apple Standard Keyboard, 108-key Apple Extended Keyboard, 101-key Enhanced keyboard, and 104-key Windows Keyboard. The most common of these is the 104-key Windows Keyboard.

A typical keyboard has four primary categories of keys. These are typing, control, numeric, and function keys. The typing keys are the letter keys. They are used most often. The control keys were added to allow control of the cursor and screen. Common control keys are the arrow keys, Insert, Delete, Home, Page Up, Page Down, Control (Ctrl), Escape (Esc), and Alternate (Alt). The numeric keys are number keys typically found at the far right of a keyboard. They are a series of 17 keys arranged like a common calculator. Finally, the function keys are assigned specific commands by your current computer application. They are found in a row at the top of the keyboard (F1 through F12).

Now that we know about the outside of a keyboard, let's venture inside. A keyboard processor has several complex parts, such as the key matrix. A key matrix is a series of circuits beneath the keys. Each circuit is broken at a certain point under the key. Pressing the key connects the circuit, which allows electric current to flow through. When the processor finds that a circuit is closed, it refers to its character map to find the location of the circuit and send its information to the computer. In its essence, a character map is a chart that tells the processor what each key in the key matrix symbolizes. For example, when you press the "a" key, it closes a circuit. The processor finds that the circuit closed is the "a" key by referring to its character map. Then, it sends the "a" to the computer.

Another complex part of the processor is its switches. Switches can be difficult to comprehend. When a switch (key) is pressed down onto the circuit, there are some small vibrations between the areas. These vibrations are known as bounce. Bounce can be confused as the rapid pressing of a key, since the circuit is rapidly switching on and off. However, the processor recognizes that you are not repeatedly pressing the key when this occurs, and filters the bounce out. So, the processor treats this as a single keypress.



What happens if you hold down a key? The processor decides that you want the key's character to be sent repeatedly. This is known as typematics. You can normally set the delay between each character on your computer software. This is known as CPS (Characters Per Second). The usual range is 2 CPS to 30 CPS.

There are several different types of switch technologies. They can be seen below:

1. Rubber Dome Mechanical- Rubber Dome Mechanical is today's most popular keyboard switch technology. Each key sits over a flexible rubber dome with a carbon center. When the key is pushed, the rubber flexes inward and pushes the carbon downward, which makes the circuit.

2. Membrane Mechanical- Membrane switches are very similar to Rubber Dome switches, except they don't have separate keys. It has one rubber sheet in each row with bulges for each key instead.

3. Capacitive Non-Mechanical- Capacitive switches are non-mechanical because they don't complete single circuits for each key. Current is always flowing through the key matrix. Each key has a tiny plate at the bottom. When the key is pressed, the plate is brought closer to another plate just below it, which changes the current at that point. The processor recognizes the key press from the change in current.

4. Metal Contact Mechanical- Metal Contact switches have a metal strip at the bottom of the key. The metal strip connects the circuit when the key is pressed.

5. Foam Element Mechanical- Foam Element switches have the same design as Metal Contact switches, except for a piece of foam holding the metal plate onto the key. This allows for better tactile response.

The processor stores the characters it needs to send to the computer in a buffer of memory as you type. Then, the data is sent to the computer through a type of connection.

There most common types of connections are:

1. 5-pin DIN Connector

2. 6-pin IBM PS/2 Mini-DIN Connector

3. 4-pin USB Connector

4. Internal Connector

Though all of the connectors are different, they each send two basic elements. The connectors supply power to the keyboard, and they send data between the keyboard and the computer. The part of the cable connector that connects to the computer is plugged into a port. This port is monitored by the computer's keyboard controller. This is a circuit that monitors all of the keyboard's data and forwards it to an operating system. The data has to be specified as either system-specific (i.e. Ctrl+Alt+Delete initiates a reboot) or application-specific (i.e. typing in Word processor).

A keyboard is a complex part of the computer. There are several different types of technologies and processes involved in just typing. The next time you type, think of everything that is involved to get the data from the keyboard to your screen. Also, be amazed by the fact that this entire process happens in a split-second! Now you know how a keyboard works.

© High Speed Ventures 2011