Input Devices

Q1. a)  What is a meant by  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)  List out the input devices used in 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.

Q2. a)  Describe  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)  Describe the following 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)  Describe how are key presses on keyboard are processed by the computer.

⇒  Each key of the keyboard contains a push-buttons underneath.

⇒  When a key is pressed, it presses a switch that completes an electric-circuit.

⇒  The electric signal so produced is converted into digital signal using analog-to-digital converter (ADC) and sent to the keyboard processor.

⇒  The Keyboard processor compares the location of key press with the index of the character (ASCII or Unicode) stored in its database.

⇒  The binary value of the key is sent to the key board buffer to wait to be processed.

⇒  Keypress generates an interrupt sinal that asks CPU to process the binary code.

⇒  The CPU either registers the keypress or take action to its corresponding letter.

In short - Each character on a keyboard has an ASCII value.
When a character is pressed, it's ASCII value in binary is sent to the computer.
The computer interprets the digital signal and displays the character on the screen.

d)  Give two alternative to keyboard to input text and explain the advantages of each method.

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

1. Speech recognition system.

Speech recognition system allows a person to read text into the system using microphone. The software picks up the correct word and input it as command to execute it, or input it as text into word processor to edit and save it as text file.

Speech recognition system can capture speech much faster than you can type and there won’t be any spelling errors.

2. Smart Pen or Digital Pen.

Smart pens make a copy of everything you write on a flat surface and save it in a digital format.

It is also possible for an artists, to immediately digitize your 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.

Q3. a)  What is  Pointing device,  give two example.

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

Examples of pointing devices include -

• Mice (or Mouse).
• Trackballs.
• Joystick.
• Light pen.
• Touch pad.

b)  Describe the input device  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 a smooth control of the graphical user interface of a computer.

c)  What is the difference between  Mechanical Ball  and  Optical mouse ?

✬   Mechanical Ball mouse : 

⇒  The mouse which contains rubber ball at its base.

⇒  When the mouse is moved, the ball rolls, and sensor inside detects its movement to move the cursor around the computer screen.

✬   Optical mouse : 

⇒  Optical mouse shines a bright red light from LED mounted on its base.

⇒  The light is reflected back from the surface into the photocell (light sensor) to detect its movement to move the cursor around the computer screen.

Q4. a)  Descirbe how the  Optical mouse  is used to control the pointer or cursor on a screen.

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

⇒  The reflected light is picked by a Light sensor (Complementary Metal Oxide Semiconductor - CMOS), which converts the light into electric pulses and send it to 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 mouse is moved on the surface.

b)  Give two advantages of  Optical mouse  over Mechanical mouse.

1. No moving parts means it won't wear out as rubber ball do.
2. Optical 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.

Microphone

Q5. a)  Describe  Microphone. 

An Input device that picks up the sound waves and convert it into digital wave.

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

b)  Describe how Microphone works.

⇒  When a microphone picks up the sound, a diaphragm vibrates, that moves the attached copper coil over the magnet.

⇒  The movement of coil over the magnetic field generates an electrical current or signal.

⇒  The analogue electrical signal is sent to the computer or recording device.

⇒  The Sound-card of the computer converts the analogue signal into digital which can then be stored or processed by the computer.

c)  Give two applications of Microphone.

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

Q6. a)  Describe how  Voice recognition  technology could be used in Security system.

⇒  Microphone picks up the user’s sound and send it to the Computer.

⇒  The Sound card converts the analogue sound into digital signal and pass it to the Security system software.

⇒  Security system software converts a few spoken words into digital wave pattern.

⇒  The input digital wave pattern is compared with the stored wave patterns.

⇒  If they match, the person will be identified.

b)  Describe how  Speech recognition  technology could be used to enabling a disabled person to communicate with a computer.

⇒  Microphone picks up the spoken words and send 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 makes 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 input it as command to the computer enabling a disabled person to communicate with it.

Digital Camera

Q7. a)  What is  Digital Camera,  explain ?

✬  A Digital camera is a camera that captures photographs in digital memory.
Unlike traditional camera that captures images in photosensitive films which require developing and then printing before 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 -

1. Focus the image automatically.
2. Operate the flash automatically.
3. Adjust the shutter speed.
4. Adjust the aperture size.
5. Adjust the size of the image.
6. Remove 'red eye' when the flash has been used.
... and so on.

b)  Describe  how Digital Camera is used to capture and store 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 are referred to as Pixels, since they are the smallest addressable area of the image.

⇒  This Charge Couple Device (CCD) converts the light into electric signals which is then passed through an analogue to digital converter (ADC).

⇒  This ADC converts the analogue electric signal into digital and send 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 = 14 megabyte x 3 primary colours) to store each file].

c)  Give three advantages of digital camera over traditional camera.

1. There is no need to develop film and print out photographs - this saves money and environment.
2. It is easy just to 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.

Q8.  Describe how  Digital Camera is used to verify the identity of passenger  at airport.

✬  Digital camera is used to take the digital image of the person.

✬  Photo in a passport is scanned and is compared with the photo taken by the digital camera using Face Recognition software.

✬  The Face Recognition software compares its facial key features like width of the nose, distance between the eyes, shape of the cheek bones etc.

✬  If it matches, then the person is identified.

Barcode and QR-Code Reader/Scanner

Q9. a)  What is meant by  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)  Describe  Barcode reader/scanner. 

⇒  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 lights into digital signals.

⇒  A pattern of digital signal is decoded and send it to the computer.

c)  How does a  Barcode reader/scanner works ? 

⇒  Barcode reader shines Red-LED or Red laser light onto barcode.

⇒  Light is reflected back off the barcode into light-detecting photoelectric cells.

⇒  White area of the barcode reflects most light and the black areas reflects least of the 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)  Give three 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 database.
3. It is faster to read accurately and input data.
4. No need to price every stock items on the shelves.

Q10. a)  A shopping mall uses barcode reader at its checkout.

The checkout is linked to a stock control system. The system monitors stock levels and automatically keeps them above a minimum level.

Explain  how the stock control system automatically keeps the stock level above a minimum level .

⇒  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 sales.

⇒  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 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)  Give two benefits each to the supermarket manager and to customers of using barcode on all items.

 Manager : 

1. Easier and faster method to update item price.
2. Maintain up-to-date scales information.
3. No need to price each item therefore saves time and money

 Customer : 

1. Faster checkout / shorter queues at checkout
2. Customer gets itemised bill without error.

Q11. a)  What is meant by  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 URL's, plain text, phone numbers, email addresses etc.

b)  Describe the purpose of the three large squares at the corners of the QR code.

✬  The three large squares at the corners of the code allows the scanning device to determine the orientation of the QR Code.

✬  Top-left square works as origin and the remaining top-right and bottom-left squares is used to ensure the correct size and correct angle of the camera shot when the QR code is read.

c)  Give two difference between  Barcode  and  Quick Response (QR) code. 

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

d)  Give two 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 QR-code.

Q12. a)  Explain  how the data stored in QR-code is read using Smart phone. 

⇒  QR barcode is captured using built-in camera of the smart phone.

⇒  A beep sound comes when 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 display the message stored in the QR-barcode.

b)  Explain  how the data stored in QR-code is read by QR Reader/scanner. 

⇒  QR barcode is scanned using red laser light.

⇒  Light is reflected back.

⇒  Black squares reflects less light than white squares.

⇒  QR code application decodes and displays the messages.

Flatbed 2D Scanner & 3D Scanner :
Computed Tomography (CT) Scan & Magnetic Resonance Imaging (MRI) Scan

Q13. a)  What is meant by  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.

✬  Light-sensor used to detect and convert the reflected lights into digital image of the document.

b)  Give  different stages of scanning a document  using 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 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 Charge Couple Device (CCD) through several mirrors and lens.
5. Thousands of light-sensitive elements of CCD converts the image into electronic signals and send it to the software.
6. Software produces a digital image from the electronic form of image.

Q14. a)  Describe two ways that a document could be scanned and stored in a file on a computer.

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

b)  Give  two applications of 2D Scanner at Airport. 

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

Q15. a)  Describe  3D (three-dimensional) Scanner. 

✬  3D scanners scans solid objects and produce a three-dimensional image.

✬  It takes images at several points along three x, y and z coordinates and produces a digital image to represent a solid 3D object.

✬  The scanned images can be used in a computer aided design (CAD) or sent to a 3D printer to produce a working model of the scanned image.

b)  Give two  applications of 3D Scanner. 

1. 3D-image is used in Computer Aided Design (CAD).
2. 3D-image can be sent to a 3D-printer to produce a working solid model of the image.
3. Health care - CT and MRI Scan provides information about internal organs.
4. Education - A high-precision 3D models of real-world objects that allows students to learn and understand complex theoretical topics.
5. Security screening to check for weapons or restricted objects.
6. Industrial design and manufacturing - Quickly capture any industrial object, exported to CAD or CAM software, modify and creat 3D object using 3D printer.
7. Entertainment industry - creates digital 3D models for movies and video games.

Q16. a)  Describe  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 other to represent the 3D image of the object.

b)  Give different  types of Tomographic Scanner  and the waves it uses to penetrate the objects.

Name :	CT Scanner	MRI Scanner	SPECT Scanner
Stands for -	Computed Tomography	Magnetic Resonance Imaging	Single Photon Emission Computed Tomography
Uses :	X-ray	Radio frequencies	Gamma rays

Q17.  Describe how  MRI Scanner  is used in medical imaging.

✬  MRI stands for Magnetic Resonance Imaging.

✬  It uses strong magnetic field and highly penetrative radio waves to scan a solid object and take a series of thin slices of 2D cross-sectional images.

✬  Each slice of 2D-image is stored as digital image in computer memory.

✬  The entire series of 2D-images are combined one over other to form digital 3D image of the object.

Q18.  How  SPECT Scanner is different from MRI Scanner  in medical imaging.

✬  SPECT (Single Photo Emission CT) is a type of nuclear imaging scan, It uses radioactive tracers that are injected into the blood to emit Gamma Rays and special Camera picks up the signal to create 3D image.

✬  MRI uses Radio waves to capture and shows the physical anatomy of the organ; SPECT shows how it works by detecting the flow of blood to that organ.

Touch Screen Monitors :

There are three major types of touchscreen technologies applied to mobile phone screens :

1. Resistive.
2. Capacitive.
3. Infra-red.

Q19. a)  Describe  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 onboard microprocessor.

b)  Give two advantages and disadvantages of Resistive touchscreen technology.

✬   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 little harder).
3. Flexible top layer of Polyethylene can be damaged easily.

Q20. a)  Describe  Capacitive touchscreen  techonology.

⇒  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 electric field between the glass plates.

⇒  When the top glass layer is touched, the current changes (as human body is an electric conductor).

⇒  The coordinates where the screen is touched is then calculated by an on-board microprocessor.

b)  Give two advantages and disadvantages of Capacitive touchscreen technology.

✬   Advantages : 

1. It allows multi-touch capability.
2. Screen visibility is good in strong sunlight.
3. Very durable screen that have 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).

Q21.  Infra-red touchscreen uses either optical or heat sensitive technology.

a)  Describe  Infra-red Optical touchscreen  technology.

⇒  Infra-red touchscreen contains an array of Infra-red LEDs and Sensors fixed around the edges of the device to form a grid.

⇒  These LEDs constantly emits 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 beams.

⇒  The position where the screen is touched is then calculated by an on-board microprocessor.

b)  Describe  Infra-red 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 detects 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)  Give two advantages and disadvantages of Infra-red touchscreen technology.

✬   Advantages : 

1. Both optical and heat sensitive allows 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).

Automatic Data capturing devices :

Q22.  Describe the following  automatic data capturing devices. 

 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 inbuild processor of the Magnetic Stripe Reader.

 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 to transmit by RFID-Reader activates the RFID Chip or Tag attached to an remote objecct.

⇒  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 the object out of sight without any physical contact. The application of RFID are -

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

 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 a 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 forcasting system.
• Monitoring Air or Water pollution.
• Airplane Flight recorder (Black box).

SENSORS : Monitoring & Control System.

Q23. a)  Describe  Sensor. 

✬  A sensor is a 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 send it a monitoring or control system.

✬  Sensor is a Analogue device which needs Analogue to Digital Converter (ADC) to convert analogue signals to digital, which a microprocessor or microcontroller can understand and process.

b)  Why do we need sensors ? What are its benefits?

✬  We need sensors to monitor and control a system automatically.

✬  It could be used in dangerous environment where human can not reach like chemical or nuclear reactor, etc.

✬  It is used to measure the quantities very quickly, very accurately without errors.

✬  It helps to avoid human error.

c)  Describe and give different  applications for the following Sensors. 

Sensor	Description of Sensor	Application
Temperature	measures temperature of the surroundings by sending signals; these signals will change as the temperature changes.	✬  control/monitor temperature in a greenhouse. ✬  control/monitor a chemical process. ✬  control of a central heating / air conditioning system.
Moisture	measures water level in - for example Soil (it is based on the electrical resistance of the sample being monitored).	✬  control/monitor moisture levels in soil in a greenhouse. ✬  monitor the moisture levels in a food processing factory.
Humidity	measures the amound of water vapour in - for example Air (based on the fact that the conductivity of air will change depending on the amount of water present)	✬  monitor humidity level in building/factory. ✬  monitor/control humidity level in the air in a greenhouse.
Light	it uses photoelectric cells that produces an output (in the form of an electric current) depending on the brightness of the light.	✬  switching street lights ON or OFF depending on the light levels. ✬  switch ON car headlights automatically when it gets dark.
Infrared (active)	it uses an invisible beam of infrared radiation picked up by a detector, if the beam is broken, then there will be change in the amount of infrared radiation reaching the detector (sensor)	✬  security alarm system (intruder breaks the infra-red beam). ✬  turn ON car windscreen wipers automatically when it detects rain on the windscreen.
Infrared (passive)	it measures the heat radiation given off by an object, for example, the temperature of an intruder or the temperature in a fridge.	✬  security alarm system (detects body heat). ✬  monitor the temperature inside an industrial freezer or chiller unit.
Pressure	it generates different electric currents depending on the pressure applied.	✬  weighing of lorries at a weighing station. ✬  measure the gas pressure in a nuclear reactor.
Sound / Acoustic	basically a microphone that converts the sound into electric signals/pulses.	✬  pick up the noise of footsteps in a security system. ✬  detect the sound of liquids dripping at a faulty pipe joint.
Gas	it uses various methods to detect the gas being monitored and produce outputs that vary with the oxygen or carbon dioxide level present.	✬  monitor pollution levels in the air at an airport. ✬  monitor oxygen and carbon dioxide levels in a greenhouse. ✬  monitor oxygen levels in a car exhaust.
pH Sensor	it measures the acidity through changes in voltages in, for example, Soil.	✬  monitor acidity levels in the soil in a greenhouse. ✬  monitor/control acidity levels in a chemical process.
Magnetic field	it measures changes in magnetic fields - the signal output will depend on how the magnetic field changes.	✬  used in anti-lock braking system in car (detects the rotational speed of wheels). ✬  detect magnetic field changes in mobile phones.
Proximity	it detects the presence of a nearby object.	✬  detect when a face is close to a mobile phone screen and switches OFF screen when held to the ear. ✬  automatic braking system (applies brake when a vehicle approches to close).

Q24.  Describe the  function  of the following components of the Control System.

 Analogue-to-Digital Converter (ADC) : 

⇒  An Analog-to-digital converter (ADC) is an electronic device or system that converts an analog signal which constantly changes, into digital signal (discrete values).

⇒  Sensors are analogue devices that needs ADC to convert analogue signals to digital signals that a computer can understand and process.

 Digital-to-Analogue Converter (DAC) : 

⇒  A Digital-to-analogue Converter (DAC) is an electronic device or system that converts an digital signal which are discrete in nature, into analogue signal (a continuous change in value).

⇒  Electronic devices like computer, produces digital signal represented by 0's and 1's, whereas mechanical equipments usually uses analogue signals. So, DAC is needed to convert digital signal to analogue.

 Actuator : 

⇒  Actuator is an output device that converts electrical energy into mechanical movement.

⇒  It is controlled by microprocessor, which gives the ability to computers and other electronic devices to do some physical work.

Q25. a)  Describe how Sensors and Microprocessor are used in  Monitoring  and  Control  system.

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 signal to sound alarm/produce a warning message message,
   or controls the system by sending signal to the actuator to switch ON/OFF the valves, motors, etc.

b)  Give difference between Monitoring system and Control system.

 Monitoring system : 

⇒  Output of monitoring system do not affect the input.

⇒  Monitoring system collects data, process and reports only the processed information.

Example :

1. Monitoring pollution level in a river.
2. Monitoring of intruders in a burglar alarm system.
3. Monitoring a patient in a Hospital for vital signs, such as heart rate, temperature, etc.

 Control system : 

⇒  Output data is feedback to the system to maintain a stable condition continuously without human intervention. Hence, Output of the control system affects the input.

⇒  Control system uses the monitored data, to bring changes to the system, to maintain certain conditions of the system.

Example :

1. Controlling the temperature in a central heating / air conditioning system.
2. Turning street lights ON at the night and turning them OFF again during daylight.
3. Chemical process control (for example, maintaining temperature and pH of the processsor).

Q26. a)  Describe  how a Burglar alarm monitoring system works. 

1. The Infra-red sensor picks up the movement of an intruder in the building and send it to the microprocessor.
2. The sensor data is passed through ADC (analogue to digital converter) if it is an analogue form to produce digital data.
3. Microprocessor or computer compares reading with stored values.
4. If input values is beyond the acceptable rang, then the computer sends 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)  Give two advantages of using this monitoring system.

Advantages :

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 computer never get tired.

Q27.  Street light is controlled automatically. A light sensor and a microprocessor are used to decide when to switch each street light ON or OFF.

a)  Describe how the sensor, microprocessor and light interacts, in  Street light Control system,  to switch the street light ON or OFF.

1. The Light sensor captures the light intensity of the surrounding and send 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 sensor’s reading with stored values.
4. If Light intensity is less than the stored limit then microprocessor sends 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)  Describe how the microprocessor stops the street lights being frequently switched ON or OFF due to brief changes in the light intensity.

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

Q28.  Describe how an  Anti-lock braking system  works.

Anti-lock braking system (ABS) on car use magnetic field sensors to stop the wheels locking up on the car if the brakes have been applied too sharply.

1. When one of the car wheels rotates too slowly (i.e. it is locking up), a magnetic field sensor sends data to the microprocessor.
2. The microprocessor checks the rotation speed of the other three wheels.
3. If they are different (i.e. rotating faster), the microprocessor sends a signal to the braking system :

   ✬  and the braking pressure to the affected wheel is reduced.

   ✬  the wheel’s rotational speed is then increased to match the other wheels.

4. Checking the rotational speed using these magnetic field sensors is done several times a second and the braking to all the wheels can be constantly changing to prevent any of the wheels locking up under heavy braking; this is felt as a ‘judder’ on the brake pedal as the braking system is constantly switched OFF and ON to equalize the rotational speed of all four wheels.
5. If one of the wheels is rotating too quickly, braking pressure is increased to that wheel until it matches the other three.