Input & Output Devices

Input Devices: A Major Component of a Computer

Input devices are essential components of a computer that send data to the Central Processing Unit (CPU) for processing. The processed information is then sent to the output devices.

Let’s take a closer look at some common input devices:

Keyboard

The most commonly found input device is the keyboard.

You’ve probably already seen and used one.
It is used to enter text into the computer.

Mouse

This is another familiar input device—the mouse.

It is a pointing device that controls the cursor.

Joystick

The joystick is a control device often found in children’s play zones.

It is used for controlling video games.

Light Pen

The light pen is a light-sensitive pointing device.

It was used with older CRT monitors for highlighting text on the screen.

Trackball

The trackball works similarly to a mouse, but instead of moving the entire device, you roll a movable ball on top.

Trackballs are rarely used but can replace a mouse in some cases.

Scanner

A scanner captures or scans images for computer editing.

Lets know more about Scanners:-

How a Typical Scanner Works

Your average scanner operates using a Charge-Coupled Device (CCD), a technology designed to convert light into an electrical charge that can be processed as digital data by your computer. Here’s the step-by-step process:

The Light Source:
- When scanning begins, a bright light (often from a Xenon lamp or cold cathode) illuminates the document.
- Fun fact: Cold cathode lamps were once popular for PC case lighting!
Reflection and Focus:
- Light reflects off the document’s surface and bounces through a series of mirrors beneath the glass.
- This reflected light is then focused onto a CCD array using a lens.
Capturing the Image:
- The CCD sensors measure the light intensity.
- Darker areas (like text and images) reflect less light, while lighter areas reflect more. This creates a digital representation of your document.
Output to Your Computer:
- The scanner sends this digital data to your computer, creating a precise, high-resolution image of your document.

Understanding Scanner Resolution

The resolution of a scanner depends on the number of sensors in the CCD array.
More sensors = More points of light captured = Higher resolution.
When buying a scanner, ensure the hardware resolution is genuine and not inflated by software interpolation (which averages nearby pixels to fake a higher resolution).

Color Scanning

Color scanning involves:

Using lenses and color filters to split the image into red, green, and blue layers.
These layers are processed together to recreate the original document’s colors.
Modern scanners achieve this in a single pass, but older models required multiple passes, making them slower in color mode.

Alternative Scanner Technology: CIS vs. CCD

Not all scanners rely on CCD technology. Some use Contact Image Sensors (CIS):

CIS scanners use an array of LEDs to illuminate the document and a sensor to capture the image directly.
While more compact, lightweight, and efficient (even USB-powered), CIS scanners generally produce lower-quality scans compared to CCD-based models.
You’ll often find CIS technology in portable or small-format scanners.

Other Types of Scanners

Drum Scanners: Used in professional applications for their superior dynamic range and quality.
3D Scanners: Capture the geometry of objects for creating 3D models.

Passport Scanner

These scanners are designed for quick scanning of passports, ID cards, resident permits, and driving licenses.

Commonly found in airports, security posts, and hotels during check-ins.

Pen Scanner

The pen scanner is used to enter printed text from magazines, newspapers, and letters into the computer.

Slide the pen over text, and it appears on your screen within seconds.
Particularly useful for reading large numbers or entering small text portions into word processors, where manual entry may result in errors.

Plotters

What is a Plotter?

A plotter is an output device specifically designed to produce high-quality graphics and precise diagrams. Unlike printers, which rely on raster scan technology, plotters operate using vector scan technology.

Printer vs. Plotter: Key Differences

Raster Scan (Printer):
- A printer covers the entire page area during the printing process.
- It scans line by line, printing where required and skipping blank spaces.
- This is known as raster scanning, which is common in most conventional printers.
Vector Scan (Plotter):
- A plotter doesn’t scan the whole page. Instead, it directly moves to the specific areas where diagrams or images need to be drawn.
- It precisely plots points, lines, circles, or other geometric shapes based on the instructions from the computer.

How Plotters Work

In color plotters, the carriage holds multiple pens of different colors and widths. A built-in microprocessor receives instructions from the computer to execute commands, such as:

Move: The pen lifts and moves to a new position.
Draw: The pen stays in contact with the paper and draws shapes or lines.

Types of Plotters

1. Flatbed Plotter

The paper remains flat and stationary on the surface.
The pen holder moves horizontally and vertically, covering the entire page to draw the design.
Components include:
- Pen Holder: Holds the pen in place.
- Carriage: Moves the pen holder in different directions to access all areas of the paper.

2. Drum Plotter

The paper is rolled around a cylindrical drum, which rotates as the pen moves across the surface.
This method allows for handling large sheets of paper, making drum plotters ideal for architectural drawings or engineering designs.
Here, the paper scrolls while the pen moves, drawing the required diagrams.

Key Advantages of Plotters

Precision: Ideal for detailed designs such as architectural plans, engineering schematics, and maps.
Large Format Printing: Can handle larger paper sizes compared to standard printers.
Multicolor Capability: Equipped with multiple pens of varying colors and widths for vibrant and detailed outputs.

Recap: Plotters vs. Printers

Printers rely on raster scan technology, scanning the entire page in sequence.
Plotters operate using vector scan technology, directly moving to specific points on the paper.
Plotters are better suited for creating detailed and high-precision graphics.

Barcode Reader

An input device that can:

Read printed barcodes.
Decode the data in the barcode.
Send the data to a computer.
It is an essential device in shopping malls and retail stores.

OMR Reader

The OMR Reader stands for Optical Mark Recognition.

It is commonly used for reading OMR sheets, such as in exams with multiple-choice questions.
The scanner reads pencil or pen marks on the OMR sheets, enabling instant evaluation of answers.

Graphics Tablet

A graphics tablet allows users to hand-draw images using a special pen-like stylus.

The images are then displayed on the computer monitor.

Webcam

Webcams have become very popular and are found in almost every home.

They can be used for recording videos and during live video sessions on the internet.

Output Devices: Another Major Component of a Computer

What Are Output Devices?

Output devices receive processed information from a computer and present it to users in various formats. Let’s explore some of the most common and unique output devices:

Monitor

The monitor is the display screen that shows output from the computer.
Types of monitors include:
- CRT monitors
- LCD monitors

Now know more about LCD :-

What is Liquid Crystal Display (LCD)?

Liquid Crystal Display (LCD)—a technology widely used in electronic devices.

Let’s break it down step by step.

What is LCD?

A Liquid Crystal Display is a flat-screen display used in devices like:

Laptops
Computers
TVs
Cell phones, and more.

From the term liquid crystal, we know that it’s a state between liquid and solid:

Flows like a liquid
Exhibits some properties of solids

Key Characteristics of LCDs:

Thinner than other displays
Consumes less power

Molecular Arrangement

Solid: Molecules are perfectly aligned.
Liquid: Molecules have no proper alignment.
Liquid Crystal: Molecules show some degree of alignment.

Construction of an LCD

An LCD consists of:

Two Polarizers:
- Acts as filters.
- Allows light waves of specific polarization while blocking others.
Two Transparent Electrodes:
- Made of indium tin oxide.
- External potential is applied through these electrodes.
Two Glass Sheets:
- Holds the liquid crystal in place.
Liquid Crystal Layer:
- Positioned between the glass sheets.

Working Principle of LCD

LCDs work based on the blocking of light. Note: Liquid crystals do not produce light; instead, they require:

External light source
External power supply

How it Works:

No Bias Applied:
- The molecular arrangement of the liquid crystal remains undisturbed, allowing light to pass through.
External Bias Applied:
- The molecular arrangement is disturbed, blocking the light.
- This creates darker areas on the screen, while other areas remain clear.

Types of LCDs

Positive LCDs:
- Segments appear dark, and the background is white.
Negative LCDs:
- Segments appear white, and the background is dark.

Advantages of LCDs

Thin and compact design
Low power consumption
Less heat emission during operation
Affordable production costs

Disadvantages of LCDs

Slow speed of operation
Shorter lifespan
Restricted viewing angles, making it hard to view from certain positions

Applications of LCDs

LCDs are widely used in:

Digital wristwatches
Digital cameras
Numerical counters
Calculators
Televisions
Mobile screens
Video players
Image sensing circuits

Plasma Display

Plasma Displays—how they work, their features, and what makes them unique compared to traditional LCDs. Let’s get started!

How Plasma Displays Work

Each pixel in a plasma display is illuminated by a small amount of plasma (charged gas), similar to a tiny neon light.

Key Difference from LCD Displays:

Plasma Display:
- Individual pixels can turn on and off, resulting in deeper, truer blacks and a higher contrast ratio.
LCD Display:
- Uniformly backlit at all times, which can limit the depth of black colors.

Plasma Display Composition

A plasma display consists of multiple layers, including:

Front Plate Glass
Display Electrodes
Dielectric Layer
Phosphor-Coated Plasma Cells
Address Electrodes
Another Dielectric Layer
Rear Plate Glass

These layers work together to produce bright and vivid images.

Advantages of Plasma Displays

Plasma displays offer several benefits over LCDs, such as:

Wider Viewing Angles:
- Consistent image quality, even when viewed from the sides.
Less Visible Motion Blur:
- Ideal for fast-moving content like sports and action movies.
Faster Response Time:
- Smooth transitions between frames.
Superior Brightness Uniformity:
- More consistent brightness across the screen.

Disadvantages of Plasma Displays

Despite their advantages, plasma displays have some drawbacks:

Screen Burn-In:
- Prolonged display of static images can cause permanent marks on the screen (though improved in newer models).
Luminosity Degradation:
- Early plasma displays often lost brightness over time; however, advancements have minimized this issue.
Higher Power Consumption:
- Plasma displays typically use more electricity compared to LCDs.

Conclusion

Plasma displays are known for their superior image quality, wider viewing angles, and fast response times.

Printer

A printer is another familiar output device.
It is used to print documents and other content on paper.

Plotter

Plotters are special types of printers that produce high-quality prints on large sheets.
They are commonly used to create decorated banners.

Projector

Projectors are often seen in seminars and conference halls.
They display videos and presentations on large screens.

Headphones

Headphones are small speakers that plug into a computer line or directly into speakers.

Speakers

Speakers are used to produce high-volume audio output.
Laptops generally come with built-in speakers.

Braille Reader

A braille reader assists visually challenged individuals to read text displayed on a computer monitor.
It converts the on-screen output into braille by raising small pins, making the text readable through touch.

Virtual Reality (VR): The Future of Output Devices

Here’s an exciting pinch of information: Virtual Reality is an emerging technology that immerses you in an entirely virtual world.

Special devices are used to achieve virtual reality, including:

Virtual Reality Headset

The headset places a screen in front of your eyes, covering them entirely to provide a perfect 3D experience.
Applications include video games, simulators, and training systems.

Virtual Reality Controllers

These controllers make it feel like you’re using your own hands in the virtual world.
They allow you to interact with and control virtual objects.

Virtual Reality Gloves

VR gloves are designed to give you a sense of realistic touch in the virtual environment.