| Keyboard | Mouse | Scanner | Joystick |
KEYBOARD
The part of the computer that we come into most contact with is probably the piece that we think about the least. A keyboard is a series of switches connected to a microprocessor that monitors the state of each switch and initiates a specific response to a change in that state.
 

A typical keyboard has four basic types of keys:

  • Typing keys
  • Numeric keypad
  • Function keys
  • Control keys

The typing keys are the section of the keyboard that contain the letter keys, generally laid out in the same style that was common for typewriters ¡V The QWERTY layout.

The numeric keypad is designed for speedy numeric data entry. This set of 17 keys include 0-9, +, -, *, /, ., Enter and Num Lock.

The function keys are arranged in a line across the top of the keyboard, which could be assigned specific commands by the current application or the operating system.

 

The control keys provided cursor and screen control. The 4 direction keys ¡ö¡ô¡õ¡÷are arranged in an inverted T formation, between the typing keys and numeric keypad, which allow user to move the cursor on the display in small increments. There are other control keys allow user to make large jumps in most applications, for example:

  • Home
  • End
  • Insert (Ins)
  • Delete (Del)
  • Page Up
  • Page Down
  • Control (Ctrl)
  • Alternate (Alt)
  • Escape (Esc)
Portable computers such as laptops quite often have custom keyboards that have slightly different key arrangements than a standard keyboard. Also, many system manufacturers add specialty buttons to the standard layout.
 

Inside the keyboard

The key matrix is the grid of circuits underneath the keys. In all keyboards except for capacitive ones, each circuit is broken at the point below a specific key. Pressing the key bridges the gap in the circuit, allowing a tiny amount of current to flow through. The processor monitors the key matrix for signs of continuity at any point on the grid. When it finds a circuit that is closed, it compares the location of that circuit on the key matrix to the character map, which tells it what the key (or the combination of keys) at x,y coordinates in the key matrix represents.

 
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MOUSE
 
Throughout our computing life, we reach out for the mouse whenever we want to move the cursor or activate something. The mouse senses our motion and our clicks and sends them to the computer so it can respond appropriately.
 

Inside a Mouse

The main goal of any mouse is to translate the motion of our hand into signals that the computer can use. Almost all mice today do the translation using five components:

A ball inside the mouse touches the desktop and rolls when the mouse moves.

Two rollers inside the mouse touch the ball. One of the rollers is oriented so that it detects motion in the X direction, and the other is oriented 90 degrees to the first roller so it detects motion in the Y direction. When the ball rotates, one or both of these rollers rotate as well.

 

The rollers each connect to a shaft, and the shaft spins a disk with holes in it. When a roller rolls, its shaft and disk spin. On either side of the disk there is an infrared LED and an infrared sensor. The holes in the disk break the beam of light coming from the LED so that the infrared sensor sees pulses of light.

An on-board processor chip reads the pulses from the infrared sensors and turns them into binary data that the computer can understand. The chip sends the binary data to the computer through the mouse's cord.

The logic section of a mouse is dominated by an encoder chip, a small processor that reads the pulses coming from the infrared sensors and turns them into bytes sent to the computer.
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SCANNER
 

4 kinds of scanner

  • Flatbed scanners, also called desktop scanners, are the most versatile and commonly used scanners.
  • Sheet-fed scanners are similar to flatbed scanners except the document is moved and the scan head is immobile.
  • Handheld scanners use the same basic technology as a flatbed scanner, they do not provide good image quality. However, it can be useful for quickly capturing text.
  • Drum scanners are used by the publishing industry to capture incredibly detailed images.
 

The basic principle of a scanner is to analyze an image and process it in some way. Image and text capture (optical character recognition or OCR) allow you to save information to a file on your computer.

Parts of a typical flatbed scanner include:

¡DCharge-coupled device (CCD) array ¡DMirrors
¡DScan head ¡DGlass plate
¡DLamp ¡DLens
¡DCover ¡DFilters
¡DStepper motor ¡DStabilizer bar
¡DBelt ¡DPower supply
¡DInterface port(s) ¡DControl circuitry

 
The core component of the scanner is the CCD array. CCD is a collection of tiny light-sensitive diodes, which convert photons (light) into electrons (electrical charge). The image of the document that you scan reaches the CCD array through a series of mirrors, filters and lenses.
 

Scanning Process

The document is placed on the glass plate and the cover is closed. The inside of the cover in most scanners is flat white, although a few are black. The cover provides a uniform background that the scanner software can use as a reference point for determining the size of the document being scanned.

A lamp is used to illuminate the document.

 

The entire mechanism (mirrors, lens, filter and CCD array) make up the scan head. The scan head is moved slowly across the document by a belt that is attached to a stepper motor. The scan head is attached to a stabilizer bar to ensure that there is no wobble or deviation in the pass. Pass means that the scan head has completed a single complete scan of the document.

The image of the document is reflected by an angled mirror to another mirror.

The last mirror reflects the image onto a lens. The lens focuses the image through a filter on the CCD array.
The filter and lens arrangement vary based on the scanner. Some scanners use a three pass scanning method. Each pass uses a different color filter (red, green or blue) between the lens and CCD array. After the three passes are completed, the scanner software assembles the three filtered images into a single full-color image.

 
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JOYSTICK
 
Joysticks pull off a really neat trick. They take something entirely physical -- the movement of your hand -- and translate it into something entirely mathematical -- a string of ones and zeros (the language of computers).
 

How a joystick work

This basic design consists of a stick that is attached to a plastic base with a flexible rubber sheath. The base houses a circuit board that sits directly underneath the stick. The circuit board is made up of several "printed wires," which connect to several contact terminals. Ordinary wires extend from these contact points to the computer.

The printed wires form a simple electrical circuit made up of several smaller circuits. The circuits just carry electricity from one contact point to another. When the joystick is in the neutral position -- when you're not pushing one way or another -- all but one of the individual circuits are broken.

Each broken section is covered with a simple plastic button containing a tiny metal disc. When you move the stick in any direction, it pushes down on one of these buttons, pressing the conductive metal disc against the circuit board. This closes the circuit -- it completes the connection between the two wire sections. When the circuit is closed, electricity can flow down a wire from the computer (or game console), through the printed wire, and to another wire leading back to the computer.

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