Input and Output Devices

Ethan Sawyer

The mouse is the most known about input device, the mouse is able to work on almost any surface, the mouse has a small, red light-emitting diode (LED) that bounces light off that surface onto a complementary metal-oxide semiconductor (CMOS) sensor.The CMOS sensor sends each image to a digital signal processor (DSP) for analysis. The DSP, operating at 18 MIPS (million instructions per second), is able to detect patterns in the images and see how those patterns have moved since the previous image. Based on the change in patterns over a sequence of images, the DSP determines how far the mouse has moved and sends the corresponding coordinates to the computer. The computer moves the cursor on the screen based on the coordinates received from the mouse. This happens hundreds of times each second, making the cursor appear to move very smoothly.

Input - Mouse

The keyboard is the second most known about input device, the keyboard is able to work on any surface. A computer's keyboard is a small computer in its own right, complete with a processor and other circuitry to interpret your keystrokes. Most of this circuitry runs the computer's key matrix, which is the grid of circuits beneath the keys. In most keyboards, these circuits are incomplete under each key. When you press a key, it completes the circuit and allows an electrical current to pass through. The processor detects that completed circuit and compares its location on the key matrix with the character map, or lookup table, which tells the processor what that keystroke represents.

Input - Keyboard

A touchpad allows users to drag their fingers along in the direction they want the mouse pointer to go. It does this by sensing the pressure of the finger along a vertical and horizontal electrode grid just beneath the surface "skin." AC travels through the electrodes to the circuits. These circuits check the capacitance of both grid layers against each other. This determines where the pointer is and where it should be moved to. It's sort of an electronic version of triangulation in that the touchpad has to take your three-dimensional movements, figure out where your finger is and where it's going, and then translate this into two-dimensional movement of the pointer on the screen.

Input - Touch Pad

Output - Screen - LCD LCD technology works by blocking light. An LCD is made of

two pieces of polarized glass that contain a liquid crystal material between them. A backlight creates light that passes through the first piece of glass. At the same time, electrical currents cause the liquid crystal molecules to align to allow varying levels of light to pass through the second piece of glass and create the images you see. These monitors have several advantages over the traditional cathode ray tube (CRT) technology. LCDs have a slimmer design and consume less energy. Plus, they have a much better resolution (the number of individual dots of color, called pixels contained in a display.) They also give less eyestrain because they don't display a flicker like CRT monitors do. And they are more adjustable, you can adjust the height, tilt or swivel or mount them on a wall.

Output - Projector - LCD LCD stands for Liquid Crystal Display. The way this places an image on

a screen is fascinating and not nearly as complex as you might imagine. A bulb is set up to shine a fairly powerful light through a prism. The prism splits the light into its component colors and these are sent through small LCD screens. The screens themselves are sent signals to allow just so much of the light through at specific pixel locations. The light is then beamed through a lens onto a screen where the images can be seen by the human eye. One of the first advantages of digital LCD projectors deals with colour saturation. LCD designs generate better colour saturation than DLP designs. This is because DLP projectors aim too boost brightness at the expense of colour saturation. Therefore, digital LCD projectors will provide an image that is more rich. One of the first disadvantages of digital LCD projectors is pixilation. These projectors produce images using individual pixels which can become visible on large screens. This will give the appearance of looking through a screened door when using digital LCD projectors on large screens. This is normally a problem when watching video instead of looking at data.

Output - Speakers

When speakers are at work, an electric signal reproduced by an amplifier passes through the speaker wire which varies in terms of its frequency and its power. The signal enters the speaker through the binding posts and the wiring inside the cabinet and is sent to the voice coil. The force on the voice coil undulates back and forth, as the signal's amplitude and frequency changes. The voice coil rapidly vibrates along the axis of the magnet structure causing the cone to vibrate. The air molecules immediately around the cone are pressurized and they translate into the sounds we hear.

Speakers are usually provided with the computer, they're very simple to operate, they help blind people who would otherwise have difficulty using a computer, they can be useful for alerting computer users, even when they're busy, such as in pop-ups. But, they can take up a fair amount of desk-space, compared to headphones and they can distract people around you therefore disrupting a communal work area.