3.2 Input and Output Devices

(a) Input Device:

An Input device is a hardware device that allows data to be input into a computer. It provides data and control signals to interact with the computer.

(b) Input devices used in a computer system:

• Keyboard.
• Pointing devices (such as Mouse).
• Microphone.
• Digital Camera.
• Barcode reader.
• Quick Response (QR) Code Reader.
• 2D and 3D Scanner.
• Touchscreens.
• Automatic Data Capturing devices (such as Radio Frequency Identifier (RFID), Data Logger).
• Sensors.

(a) Keyboard:

⇒ The most common input devices, used to input data like text, symbols and numbers into applications software.

⇒ They are also used for typing in commands to the computer (e.g. Prnt Scrn to take a screenshot, Ctrl + P to print out, etc.).

(b) Types of Keyboard:

1. QWERTY Keyboard: The most common type of standard keyboard, whose name comes from the keys on the top row which spell out 'QWERTY'.
2. Ergonomic Keyboard: A keyboard designed to reduce health-related problems associated with the standard keyboard (e.g. Repetitive Strain Injury). Its keys are arranged differently to give more support to the wrists and hands when doing a lot of typing.
3. Braille Keyboard: A special type of keyboard, usually featuring raised dots, that is used by visually impaired people to enter data into the computer.

(c) How key presses on a keyboard are processed by the computer:

1. Each key of the keyboard contains a push-button underneath.
2. When a key is pressed, it presses a switch that completes an electric circuit.
3. The electric signal so produced is converted into digital signal using an Analogue-to-Digital Converter (ADC) and sent to the keyboard processor.
4. The keyboard processor compares the location of key press with the index of the character (ASCII or Unicode) stored in its database.
5. The binary value of the key is sent to the keyboard buffer to wait to be processed.
6. Key press generates an interrupt signal that asks CPU to process the binary code.
7. The CPU either registers the key press or takes action corresponding to its letter.

(d) Two alternatives to keyboard to input text:

An alternative to keyboard is to lay words down by speaking or writing with a smart pen.

Method 1: Speech recognition system

• Description: Speech recognition system allows a person to read text into the system using a microphone. The software picks up the correct word and inputs it as a command to execute it, or inputs it as text into a word processor to edit and save as a text file.
• Advantage: Speech recognition system can capture speech much faster than you can type and there won't be any spelling errors.

Method 2: Smart Pen or Digital Pen

• Description: Smart pens make a copy of everything you wrote on a flat surface and save it in a digital format.
• Advantage: It is also possible for an artist to immediately digitize sketches for editing. Some of the best smart pens also come with voice recorders built-in, which helps to take notes and record a speaker at the same time.

(a) Pointing device:

A pointing device is a device with which you can control the movement of the pointer in a GUI (Graphical User Interface) to select an item on the display screen.

Examples of pointing devices include:

• Mice (or Mouse)
• Touchpad / Trackball

(b) Mouse:

⇒ A computer Mouse (plural: Mice) is a hand-held pointing device that detects two-dimensional motion relative to a surface.

⇒ This motion is typically translated into the motion of a pointer on a display, which allows smooth control of the graphical user interface of a computer.

(c) Difference between Mechanical Ball mouse and Optical mouse:

(a) How an Optical mouse controls the cursor:

⇒ Optical mouse uses a red LED light at its base, flashed over and bounced back from the surface.

⇒ The reflected light is picked up by a Light sensor (CMOS — Complementary Metal Oxide Semiconductor), which converts the light into electric pulses and sends it to a DSP (Digital Signal Processor).

⇒ The DSP processor calculates the coordinates and controls the pointer based on the changing electric pulse or image patterns generated as the mouse is moved on the surface.

(b) Advantages of Optical mouse over Mechanical mouse:

1. No moving parts means it won't wear out as rubber ball do.
2. Optical mice don't require a special surface, such as a mouse pad.
3. Dirt cannot get inside the mouse and interfere with the tracking sensors.
4. Increased tracking resolution means smoother response.

(a) Microphone:

⇒ An input device that picks up sound waves and converts them into a digital wave.

⇒ Microphones are either already built within the computer system or connected externally by USB port or using wireless connectivity.

(b) How a Microphone works:

1. When the microphone picks up the sound, a diaphragm vibrates, which moves the attached copper coil over the magnet.
2. The movement of the coil over the magnetic field generates an electrical current or signal.
3. The analogue electrical signal is sent to the computer or recording device.
4. The Sound-card of the computer converts the analogue signal into digital which can then be stored or processed by the computer.

(c) Applications of Microphone:

1. Voice recognition system — to identify a person by a security system.
2. Speech recognition system — enabling a disabled person to communicate with a PC.
3. Doing a Voice over in a presentation.

(a) Voice recognition in a Security system:

• Microphone picks up the user's sound and sends it to the computer.
• The Sound card converts the analogue sound into digital signal and passes it to the Security system software.
• Security system software converts a few spoken words into a digital wave pattern.
• The input digital wave pattern is compared with the stored wave patterns.
• If they match, the person will be identified.

(b) Speech recognition for a disabled person:

• Microphone picks up the spoken words and sends it to the computer.
• The Sound card converts the analogue sound into digital signal.
• The software takes the digital data and breaks it up into Phonemes (smallest elements that make up a language).
• These phonemes are compared with words found in the built-in dictionary and suggest a few equivalent words.
• The software picks up the correct word and inputs it as a command to the computer, enabling a disabled person to communicate with it.

(a) Digital Camera:

★ A Digital camera is a camera that captures photographs in digital memory. Unlike traditional cameras that capture images in photosensitive films which require developing and then printing before the photographer could see the result.

★ Digital cameras can display images on a screen immediately after being recorded.

★ Digital images can be stored, processed, edited and deleted easily.

★ It could be connected to a computer system via a USB port or by wireless Bluetooth.

★ Digital Camera is controlled by a microprocessor which can automatically carry out the following tasks:

• Focus the image automatically.
• Operate the flash automatically.
• Adjust the shutter speed.
• Adjust the aperture size.
• Adjust the size of the image.
• Remove 'red eye' when the flash has been used.

(b) How a Digital Camera captures and stores an image:

• The photograph is captured when light passes through the lens into a Light Sensor Chip that contains an array of tiny light-sensitive cells called Charge Couple Devices (CCD).
• Each of these cells is referred to as a Pixel, since they are the smallest addressable area of the image.
• The CCD converts the light into electric signals which is then passed through an Analogue-to-Digital Converter (ADC).
• The ADC converts the analogue electric signal into digital and sends it to the software that stores it in digital image format.
• The number of pixels determines the resolution and size of the file.
• e.g. a 14-megapixel camera will need 42 megabytes (14 megapixel × 3 primary colours) to store each file.

(c) Advantages of digital camera over traditional camera:

1. There is no need to develop film and print out photographs — this saves money and the environment.
2. It is easy to just delete an image from memory if it is not satisfactory and take the photograph again.
3. The memory cards can store several hundred photographs. A traditional camera's film roll was limited by the number of photographs.
4. It is easier and faster to upload photographs to a computer.

(a) Barcode:

• A Barcode is a way to encode information into a visual pattern that a machine (barcode scanner) can read.
• Barcodes are applied to products to quickly identify them.
• It contains a series of dark and light parallel lines of varying thickness.
• The unique series of lines represents the numbers from 0 to 9.
• Each digit is made up of two dark lines and two light lines.

(b) Barcode reader/scanner:

• A Barcode reader/scanner is an electronic device that captures and decodes the information contained by a barcode.
• It flashes Red-laser or Red-LED light over the barcode to reflect back.
• The light sensor converts the reflected light into digital signals.
• A pattern of digital signal is decoded and sent to the computer.

(c) How a Barcode reader/scanner works:

• Barcode reader shines Red-LED or Red laser light onto the barcode.
• Light is reflected back off the barcode into light-detecting photoelectric cells.
• White areas of the barcode reflect most light and black areas reflect the least light.
• As the Laser or LED light is scanned across the barcode, a pattern is generated which is converted into digital data.
• This binary digital data is sent to the computer to read the decimal number contained by the barcode.

(d) Advantages of using Barcode:

1. Avoids the possibility of typing error.
2. It is much easier to change the price and other details of stock items in the database.
3. It is faster to read accurately and input data.
4. No need to price every stock item on the shelves.

(a) How the stock control system keeps stock above minimum:

• Stock control system contains a database that stores the barcode number, number of items in stock, minimum stock level and all other details of each item available for sale.
• At the checkout, the barcode of the item is scanned and is searched for that item in the database.
• Stock level of the product is reduced by 1.
• Stock level is checked against the minimum level.
• If stock level is less than the minimum level, then a purchase order is placed automatically and the record is flagged (like, Order placed? = Yes).
• When new stock is purchased, the flag is reset (like, Order placed? = No).

(b) Benefits to supermarket manager and customers:

★ Benefits to the Manager:

1. Easy to update prices centrally without re-labelling each shelf item.
2. Automatic re-ordering of stock keeps shelves filled and reduces lost sales.

★ Benefits to Customers:

1. Faster checkout — no waiting while the cashier types in each price.
2. Itemised receipt helps customers verify what they bought and at what price.

(a) Quick Response (QR) Code:

• Quick Response code is a two-dimensional barcode made up of filled-in dark squares on a light background.
• It is a machine-readable optical label that contains information about the item to which it is attached.
• It can store any numeric or alphanumeric data like website URLs, plain text, phone numbers, email addresses, etc.

QR Code showing three finder squares at top-left, top-right, bottom-left corners.

(b) Purpose of the three large squares at the corners of the QR code:

• The three large squares at the corners of the code allow the scanning device to determine the orientation of the QR Code.
• The top-left square works as the origin and the remaining top-right and bottom-left squares are used to ensure the correct size and correct angle of the camera shot when the QR code is read.

(c) Differences between Barcode and QR Code:

1. Simple one-dimensional Barcode can be read by a barcode reader only. But a smartphone can scan a QR code using its camera and built-in application.
2. Simple one-dimensional barcode can hold 30 digits, whereas two-dimensional QR code can hold up to 7000 digits.

(d) Advantages and disadvantages of QR Code:

★ Advantages:

1. No need to write important details about the product — simply scan the QR Code and capture the information.
2. Gives automatic access to the website or contact telephone number.
3. Beneficial for both customer and business to store and advertise information about the product.
4. Store boarding passes electronically at airports and train stations.

★ Disadvantages:

1. Users must be equipped with a camera phone and the correct "QR Code reader" software that can scan the image of the QR Code.
2. The customer doesn't know how to scan and use the QR code.

(a) Reading QR code using a Smartphone:

• QR barcode is captured using the built-in camera of the smart phone.
• A beep sound comes when the QR code is appropriately scanned.
• QR code reading software digitally scans the horizontal and vertical black and white squares of the QR code.
• Software decodes and displays the message stored in the QR barcode.

(b) Reading QR code by a QR Reader/scanner:

• QR barcode is scanned using red laser light.
• Light is reflected back.
• Black squares reflect less light than white squares.
• QR code application decodes and displays the messages.

(a) Flatbed 2D Scanner:

• Flatbed 2D scanner is used to make digital copies of documents or pictures.
• The document is placed on a glass plate and a bright light shines on the paper.
• A light-sensor is used to detect and convert the reflected light into a digital image of the document.

(b) Stages of scanning a document using a 2D Scanner:

1. The scanner cover is raised to place the document on a glass panel and then the cover is closed.
2. A bright light produced by a xenon lamp illuminates the document.
3. A scan head moves across the document until the whole page has been scanned.
4. An image of the document is made to fall on a Charge Couple Device (CCD) through several mirrors and a lens.
5. Thousands of light-sensitive elements of the CCD convert the image into electronic signals and send it to the software.
6. Software produces a digital image from the electronic form of image.

(a) Two ways to scan and store a document:

1. Computer equipped with OCR (Optical Character Recognition) software allows the scanned text from the document to be converted into a text file that could be edited using a word processor.
2. Scanned document could be stored as an image file, if it contains photographs or pictures.

(b) Applications of 2D Scanner at an Airport:

1. Passport or document is scanned to convert into text file using software equipped with OCR (Optical Character Recognition) for editing or comparing it with stored data.
2. Photo in a passport is scanned as an image file and is compared with the photo taken by the digital camera using Face Recognition software.

(a) Computed Tomography (CT):

• Computed Tomography (CT) is an imaging technology that produces a 3D image of a solid object.
• It scans the object by passing highly penetrating waves like X-ray, Gamma-ray, Ultra-sound or Radio waves and builds up a series of very thin slices of 2D images.
• Each slice of 2D image is stored as digital image in computer memory.
• The entire series of 2D images are combined one over the other to represent the 3D image of the object.

(b) Types of Tomographic Scanner and waves used:

(a) Resistive touchscreen technology:

• The resistive touchscreen consists of a flexible top layer made of Polyethylene and a rigid bottom layer made of glass.
• Both the layers are coated with a conducting material like Indium Tin Oxide (ITO) and then spaced with spacers.
• An electric current flows between the two layers.
• When a touch is made, the flexible screen presses down and touches the bottom layer.
• A change in electrical current is detected and the coordinates of the point of touch is calculated by the on-board microprocessor.

(b) Advantages and disadvantages of Resistive touchscreen:

★ Advantages:

1. It allows bare fingers, gloved fingers or a stylus to carry out an input operation.
2. Good resistance to dust and water.

★ Disadvantages:

1. It does not permit multi-touch.
2. Low touch sensitivity (need to press down a little harder).
3. Flexible top layer of Polyethylene can be damaged easily.

(a) Capacitive touchscreen technology:

• Capacitive touchscreen consists of many layers of glass panel coated with conducting material Indium Tin Oxide (ITO) that act like a capacitor.
• When current is passed through these layers, it creates an electric field between the glass plates.
• When the top glass layer is touched, the current changes (as the human body is an electric conductor).
• The coordinates where the screen is touched is then calculated by an on-board microprocessor.

(b) Advantages and disadvantages of Capacitive touchscreen:

★ Advantages:

1. It allows multi-touch capability.
2. Screen visibility is good in strong sunlight.
3. Very durable screen that has high scratch resistance.

★ Disadvantages:

1. It allows only bare finger or special stylus.
2. They are sensitive to electromagnetic radiation (such as magnetic fields or microwaves).

(a) Infrared Optical touchscreen technology:

• Infrared touchscreen contains an array of Infra-red LEDs and Sensors fixed around the edges of the device to form a grid.
• These LEDs constantly emit invisible Infra-red light beams to form a grid on the screen.
• Sensors are used to detect where the screen has been touched through a break in an infra-red beam.
• The position where the screen is touched is then calculated by an on-board microprocessor.

(b) Infrared heat sensitive touchscreen technology:

• Infra-red heat sensitive touchscreen contains Infra-red heat sensors fixed around the edges, over the glass screen of the device.
• Infra-red heat sensors detect the heat generated by the finger at the point of touch.
• The position where the screen is touched is then calculated by an on-board microprocessor.

(c) Advantages and disadvantages of Infra-red touchscreen:

★ Advantages:

1. Both optical and heat sensitive allow multi-touch capability.
2. Screen visibility is good in strong sunlight.
3. Optical system allows the use of bare fingers, gloved fingers and stylus for input.

★ Disadvantages:

1. Infra-red Touchscreens are expensive.
2. The heat-sensitive system only allows bare fingers (gloved fingers and stylus don't work).

(a) Magnetic Stripe Reader:

• A magnetic stripe reader is a device designed to read the information stored within the magnetic stripe, usually located at the back of the card (like Credit card, ATM card, etc.).
• Magnetic Strip over Credit/Debit card or ATM card contains the account details of the person who owns the card.
• When a card is moved over or through a magnetic stripe card reader, it induces a voltage in the coils of the device.
• This voltage is amplified so that it can be recorded electronically and read by a computer or in-built processor of the Magnetic Stripe Reader.

(b) Radio Frequency Identification (RFID):

• Radio Frequency Identification (RFID) refers to a wireless system comprised of two components: RFID-Tags (Chip) and RFID-Readers.
• RFID-Reader is an electronic device that has one or more antennas that emit radio waves and receive signals back from the RFID tag.
• The radio waves transmitted by RFID-Reader activate the RFID Chip or Tag attached to a remote object.
• When activated, the tag transmits data or information about the object to which it is attached back to the RFID-Reader.
• It is used to read information about an object out of sight without any physical contact.

Applications of RFID:

• Equipment tracking.
• Personal tracking.
• Inventory control.
• Monitoring system.

(c) Data Logger:

• Data loggers are compact, battery-powered electronic devices equipped with an internal microprocessor, data storage, and one or more sensors.
• It records data over time (for months), unattended. It can be deployed indoors, outdoors, and underwater.
• After the desired monitoring period, the data logger is then reconnected to the computer and the software is used to read out and process data.
• It is used to automatically monitor and record environmental parameters over a period of time, like:

• Weather forecasting system.
• Monitoring Air or Water pollution.
• Airplane Flight recorder (Black box).

(a) Sensor:

• A sensor is an input device used to read or measure the real-world physical quantities from its surroundings which are analogue in nature, like temperature, sound, light, pressure, etc.
• It continuously captures the signal from its surroundings and automatically sends it to a monitoring or control system.
• Sensor is an Analogue device which needs an Analogue-to-Digital Converter (ADC) to convert analogue signals to digital, which a microprocessor or microcontroller can understand and process.

(b) Why we need sensors and their benefits:

• We need sensors to monitor and control a system automatically.
• It could be used in dangerous environments where humans cannot reach, like chemical or nuclear reactors, etc.
• It is used to measure quantities very quickly, very accurately without errors.
• It helps to avoid human error.

(c) Different sensors and their applications:

(a) Analogue-to-Digital Converter (ADC):

• An Analogue-to-digital converter (ADC) is an electronic device or system that converts an analogue signal (which constantly changes) into a digital signal (discrete values).
• Sensors are analogue devices that need an ADC to convert analogue signals to digital signals that a computer can understand and process.

(b) Digital-to-Analogue Converter (DAC):

• A Digital-to-analogue Converter (DAC) is an electronic device or system that converts a digital signal (which is discrete in nature) into an analogue signal (a continuous change in value).
• Electronic devices like a computer produce digital signals represented by 0's and 1's, whereas mechanical equipment usually uses analogue signals. So, a DAC is needed to convert digital signal to analogue.

(c) Actuator:

• An Actuator is an output device that converts electrical energy into mechanical movement.
• It is controlled by a microprocessor, which gives computers and other electronic devices the ability to do some physical work.

(a) How Sensors and Microprocessor are used in Monitoring and Control systems:

1. Sensors send signals to the microprocessor/computer.
2. The sensor's analogue signals are converted into digital using ADC.
3. The computer/microprocessor analyses the data received by checking it against stored values.
4. If the input data is outside the acceptable range, then the microprocessor — either monitors the system by sending a signal to sound an alarm/produce a warning message, or controls the system by sending a signal to the actuator to switch ON/OFF the valves, motors, etc.

(b) Difference between Monitoring system and Control system:

(a) How a Burglar alarm monitoring system works:

1. The infra-red sensor picks up the movement of an intruder in the building and sends it to the microprocessor.
2. The sensor data is passed through an ADC (analogue-to-digital converter) if it is in analogue form to produce digital data.
3. Microprocessor or computer compares the reading with stored values.
4. If input values are beyond the acceptable range, then the computer sends a signal to sound the alarm, or to flash the light.
5. DAC (digital-to-analogue converter) is used if the devices need analogue values to operate.
6. The alarm continues to sound / lights continue to flash until the system is reset or switched OFF.

(b) Advantages of using this monitoring system:

1. No need to employ any human watchman, so this can save money.
2. Avoids the possibility of human errors.
3. 24/7 monitoring is possible, as a computer never gets tired.

(a) How the sensor, microprocessor and light interact to switch the street light ON or OFF:

1. The Light sensor captures the light intensity of the surroundings and sends it to the microprocessor.
2. ADC (analogue-to-digital converter) is used to convert the sensor's analogue signal to digital data.
3. Microprocessor or computer compares the sensor's reading with stored values.
4. If the light intensity is less than the stored limit, then the microprocessor sends a signal to the actuator to switch ON the light.
5. DAC (digital-to-analogue converter) is used if the devices need analogue values to operate.
6. This process continues until the system is switched OFF.

(b) How the microprocessor stops frequent ON/OFF switching:

⇒ After each time the street light is switched ON or OFF, the microprocessor waits for 5 to 10 minutes before sampling the next sensor's input of light intensity.

(a) Output Device:

An Output device is a hardware device which converts information into human-readable form.

(b) Output devices used in a computer system:

• Monitor
• Printer
• Projector
• Interactive Whiteboard / Smart board
• Headphone
• Speaker

(a) LCD (Liquid Crystal Display) Monitor:

⇒ LCD is made up of a layer of liquid crystal diodes, sandwiched between two polarizing material sheets.

⇒ It uses back lighting from cold cathode fluorescent lamp (CCFL), that illuminates the LCD panel.

⇒ Liquid crystal diodes are grouped together with three primary colours (Red, Green and Blue), to form a full colour pixel.

⇒ When an electric current is passed through the LCD panel, the liquid crystals align themselves to allow only the required light to pass and form the image on the screen.

(b) Advantages and disadvantages of LCD monitors:

★ Advantages:

1. Lightweight and compact than CRT.
2. Very low power consumption than CRT.
3. It is not affected by magnetic field.
4. It does not generate heat like CRT.

★ Disadvantages:

1. Poor viewing angle.
2. Motion blur is common.
3. It has fixed resolution.

(a) LED (Light Emitting Diode) back-lit Monitor:

⇒ LED back-lit monitor uses LCD technology, but instead of CCFL back light, it uses an array of LEDs as back light to illuminate the LCD panel.

⇒ LED back-lit monitor is thinner and more energy efficient than LCD monitor.

⇒ It provides better contrast and colour quality for a sharper image.

(b) Advantages and disadvantages of LED monitors:

★ Advantages:

1. LED back-lit monitor reaches maximum brightness quickly.
2. LED back-lit monitors are lighter and thinner than LCD monitor.
3. They produce high quality display with vivid colours and higher contrast.
4. It consumes less power than LCD.

★ Disadvantages:

1. LED is more expensive than LCD.
2. Poor viewing angle.
3. It has fixed resolution.
4. Motion blur is common.

(a) TFT-LCD (Thin Film Transistor - LCD) Monitor:

⇒ A TFT monitor uses thin-film transistor technology in an LCD display.

⇒ LCD panel is coated with a thin film of transparent semiconductor silicon layer that works as transistors.

⇒ Each pixel of LCD panel is controlled by a separate tiny transistor, to give full colour, high resolution and more contrast.

(b) Advantages and disadvantages of TFT monitors:

★ Advantages:

1. Control of thin film transistors over each pixel gives best resolution and higher image quality.
2. The resolution of LCD can be changed.

★ Disadvantages:

1. Poor viewing angle.
2. While the colours are beautiful, they aren't always very accurate.

(a) OLED (Organic Light Emitting Diode) Monitor:

⇒ OLED display uses a thin layer of Organic light emitting diodes, made up of organic compound which acts as semi-conductors (e.g. polyaniline and polyfluorene).

⇒ This flexible Organic film is sandwiched between two charged electrodes, made up of rigid glasses or flexible polymers.

⇒ When an electric field is applied to the electrodes, OLED gives its own light to form the image on the screen.

(b) Advantages and disadvantages of OLED monitors:

★ Advantages:

1. It is very thin and flexible to be bent to any shape.
2. It provides larger viewing angle (about 170 degrees).
3. Since it requires no backlighting, it uses very less power than LCD.
4. It provides brighter image with higher contrast (superior image quality).

★ Disadvantages:

1. Organic materials used degrade over time, like any organic matter.
2. It requires more power when displaying documents with white or bright backgrounds.

(a) Interactive Whiteboard / Smart Board:

⇒ Interactive Whiteboard (IWB) is a classroom tool, that allows images from a computer screen to be displayed on the board using a Digital Projector.

⇒ When connected to the computer with special IWB-software, it transforms into a touch sensitive board.

⇒ The user can write, edit and click the elements to manipulate the content with a special pen or with his finger.

⇒ The text or drawings produced are then stored in an electronic form for later use.

⇒ With the computer connected to the internet, teachers and students can access and share information around the world.

⇒ It helps the student to engage in lessons by working collaboratively.

(b) Benefits of smart boards in the classroom:

1. Enhanced Lessons: Integrate various learning styles into one experience. Students can learn better and remember more by seeing, hearing, and interacting with the board through touch.
2. Interactive Learning: Allow children to interact with the learning material through touching, drawing, or writing on the board. Educational games can be played by entire classrooms.
3. Low Maintenance: No chalk or markers are needed. Data is modified using a specialized pen for highlighting, drawing, and writing. No cleanup. It's just that easy.
4. Flexibility in the Classroom: Various media types can be displayed, whether photos, graphs, maps, illustrations, or videos — teachers have an abundance of options to create creative lessons to inspire students.
5. Connected to the Internet: Teachers have access to various sources to enhance and support their lessons.
6. Integrated Technology: Any device you can think of — like computers, microscopes, cameras, and video cameras — can be attached to the boards to enhance instruction.

(a) LCD Projector:

• LCD Projector uses LCD display technology.

• It contains three LCD panels, each panel creates an image using just one of the primary colours (red, green, and blue).

• All three coloured images are combined to form a full colour image and projected on the screen at once.

(b) How LCD Projector works:

⇒ LCD projectors work by using three LCD panels, a lamp, a prism, and polarizing filters to create the image on the screen.

⇒ A high intensity white back light from CCFL or LED is beamed, and passed through a polarizing filter.

⇒ This polarized light is then sent to a series of dichromic mirrors, which reflect the light at different wavelengths corresponding to Red, Green and Blue light.

⇒ These different coloured lights pass through three different LCD panels to produce three different coloured images.

⇒ These images are then combined using a special dichromic Prism, allowed to pass through a projector lens and produce a full colour image onto the big screen.

(c) Advantages and disadvantages of LCD Projector:

★ Advantages:

1. LCD projector is less expensive than DLP.
2. LCD projector produces sharper image than DLP.
3. LCD projector has no moving parts.

★ Disadvantages:

1. LCD projector has lower contrast ratio than DLP.
2. LCD panels being organic, they degrade over time.

(a) DLP (Digital Light Processing) Projector:

⇒ DLP projector uses millions of micro-mirrors arranged on a DLP chip that creates pixels on screen.

⇒ A bright white light source is beamed through a spinning colour filter on the DLP chip.

⇒ The white light is split into a sequence of primary colours — red, green and blue.

⇒ When the micro-mirror tilts towards the light source to reflect light on the screen, the pixel is ON, and when tilt away, the pixel is OFF.

⇒ This creates light and dark pixels of millions of coloured shades to produce an image on the screen.

(b) Advantages and disadvantages of DLP Projector:

★ Advantages:

1. DLP provides higher contrast ratio.
2. DLP projectors are lighter and portable.
3. DLP projectors require less maintenance than LCD projectors because of sealed chip design.

★ Disadvantages:

1. DLP projectors aren't as good as LCD models at rendering colours.
2. DLP projector could suffer from the "Rainbow effect" (this is due to the slow spinning speed of the Chromatic Colour filter Wheel).

(a) Inkjet Printer:

Inkjet printer is an output device that accepts processed information like text and graphics from a computer, and recreates it by spraying droplets of ink on paper or plastic substrate.

It essentially contains:

• A print-head, which consists of nozzles that spray droplets of ink onto the paper to form characters and images.
• An ink cartridge containing all three primary colours and black colour ink.
• A stepper motor and belt, which moves the print head assembly across the page from side to side.
• A paper feeder, which automatically feeds the printer with papers as they are required.

(b) Applications of Inkjet Printer:

1. Home and Office print jobs, where only a few pages of good quality colour printing is needed.
2. Photo studio print jobs, where high quality photos need to be printed.
3. Printing posters of large size.
4. Printing architecture and engineering drawings using a plotter that uses Inkjet technology.
5. Printing 3D prototypes using a 3D Printer that uses Inkjet technology.

(c) Advantages and disadvantages of Inkjet Printer:

★ Advantages:

1. Provides low cost printing.
2. High quality printing with vivid colours.
3. Can print over different types of flexible and solid surfaces.
4. Don't need warm up time.

★ Disadvantages:

1. It is not fit for large scale printing, as it contains a small ink cartridge.
2. Printing speed is not as fast as laser printers.
3. Print head is less durable, prone to clogging and damage.

(a) Thermal Bubble technology:

⇒ Thermal Bubble ink-jet contains tiny resistors at the nozzle of ink reservoir that create heat to vaporize ink.

⇒ The vaporized ink forms a tiny bubble which when expands, ejects the ink from the print head to the paper.

⇒ When the bubble collapses, it creates a small vacuum which allows fresh ink to be drawn into the print head.

⇒ This continues until the printing finishes.

(b) Piezoelectric technology:

⇒ Piezoelectric Ink-jet contains a crystal, located at the back of each nozzle of the ink reservoir.

⇒ The crystal is given a tiny electric charge which makes it vibrate.

⇒ The vibration forces the ink to be ejected on the paper and at the same time more ink is drawn in for further printing.

⇒ This continues until the printing finishes.

(a) Laser printer:

Laser printer is an output device that produces a high quality printout by using a laser beam, to form a pattern of electrostatically charged dots on a light-sensitive drum, which attract dry powder ink called toner. The toner is transferred to a piece of paper and fixed by a heating process.

Unlike Inkjet printer, Laser printer prints the whole page in one go.

(b) Printing process of Laser printer (Laser printing technology):

⇒ Laser printer uses electrostatic charge for printing.

⇒ It produces high quality printout by passing Laser beams of text and graphics over a positively charged cylindrical drum.

⇒ The bright parts of the drum lit by the projected image lose their charge and leave negatively charged area, but the dark areas keep the positive charge.

⇒ A black carbon powder called toner is positively charged.

⇒ The toner is attracted to the negatively charged area of the drum.

⇒ The drum rotates and rolls against a piece of negatively charged paper.

⇒ The toner is transferred from the drum to the paper, making a black and white image of the original.

⇒ The paper is heated which makes the toner stick to it permanently.

(c) Applications of Laser Printer:

1. Company and Office print jobs, where very fast, large volume of high quality printing is needed.
2. Producing a large number of high-quality flyers or pamphlets for advertising.
3. Large scale Book and magazine printing.

(d) Advantages and disadvantages of Laser Printer:

★ Advantages:

1. Suitable for large scale bulk printing.
2. High quality printouts, better than ink-jet.
3. Prints faster than ink-jet.
4. Cost per page is cheaper than ink-jet.
5. Prints very quietly without any sound compared to ink-jet.

★ Disadvantages:

1. It is more expensive than an Inkjet printer.
2. Larger and heavier than ink-jet printers.
3. Toner is more expensive than ink-jet cartridges.

(a) 3D Printer:

⇒ 3D printer is used to produce three-dimensional solid objects, using additive layer manufacturing and Inkjet technology.

⇒ The digital computer model of the object to be printed is created by using a 3D scanner, or by using CAD software (which provides the dimensions and shape of the object).

⇒ The solid object is built up by spraying powdered resin (synthetic organic polymer), metal or ceramic, layer over layer from bottom to top successively until final object is produced.

(b) Difference between Direct and Binder 3D printer:

(c) Applications of 3D Printer:

1. Industrial manufacturing — for printing prototypes and functional parts of machines.
2. Medical industry — for producing artificial organs like teeth, ears, legs, etc.
3. Education — printing prototypes for students to use in classes and projects.
4. Art and Jewellery making.

(d) Advantages and disadvantages of 3D Printer:

★ Advantages:

1. Produce prototypes quickly.
2. Low development cost.
3. Easy to spot and correct design errors.
4. Any complicated objects can be printed with a variety of materials.
5. Computer designs can be shared and printed by others.

★ Disadvantages:

1. 3D printers are expensive to buy.
2. Anyone can print dangerous items (like guns) without being checked.
3. Copyright issues — it is very easy to print illegal copies of items if you have its design.

(a) 3D Cutter:

⇒ 3D Cutter uses subtractive fabrication technique.

⇒ It removes the excess material from the solid block to give the shape of the object.

⇒ It uses Laser beams to simply cut a given material perfectly and clean and polish the object.

(b) Applications of 3D Cutter:

1. Laser surgery — to remove unwanted tissues from the body.
2. Industrial manufacturing — to produce laser cut products with metals like steel, tungsten, nickel, brass and aluminium.
3. Laser engraving and laser marking — used to mark or engrave all varieties of jewellery.
4. Laser cut ceramics — to produce artifacts and sculptures.

(c) Advantages and disadvantages of 3D Cutter:

★ Advantages:

1. Laser cutting offers fast, clean and accurate cuts even for small complex details.
2. Laser cutting offers freedom for the design and the quantities of product.
3. All sides of an object can be cut into.

★ Disadvantages:

1. Can be expensive to set up and maintain.
2. Output is only as good as the computer 3D model.

(a) Loudspeakers and Headphones:

⇒ Loud Speakers and Headphones are the output devices responsible for producing sounds.

⇒ It converts digital sound signals into analogue waves that are audible to our human ear drums.

⇒ It allows us to hear music, communicate with people through voice and video calls, get computer warning signals etc.

(b) How a Loudspeaker works:

1. Speaker works by converting electrical energy into mechanical energy that compresses the air to produce sound.
2. An audio signal in the form of electric current is sent through the voice coil wrapped around an iron core.
3. The voice coil generates a magnetic field in the iron core, which is attracted and repelled by the permanent magnet around it.
4. The vibration of the iron core attached to the paper cone, causes the cone to vibrate to produce the sound.

(c) How digitally-stored music can be played through analogue loudspeakers:

1. Digital sound stored on a file is passed through a Digital-to-Analogue Converter (DAC), where it is changed into an electric current.
2. This is then passed through an amplifier which increases the voltage of the sound signal large enough to drive a loudspeaker.
3. This electric current is then fed to a loudspeaker where it is converted into sound.