Learning Objectives
By the end of this lesson, you will be able to:
- Understand what is meant by aninput deviceand why it is required
- Identify and describe the purpose of:barcode scanner, digital camera, keyboard, microphone, optical mouse, QR code scanner, touch screen (resistive, capacitive and infra-red), 2D and 3D scanners
- Understand what is meant by anoutput deviceand why it is required
- Identify and describe the purpose of:actuator, DLP projector, inkjet printer, laser printer, LED screen, LCD projector, LCD screen, speaker, 3D printer
- Understand what is meant by asensorand the purposes of sensors
- Identify the type of data captured by each sensor and understand when each sensor would be used
- Select the most suitable sensor for a given context from:acoustic, accelerometer, flow, gas, humidity, infra-red, level, light, magnetic field, moisture, pH, pressure, proximity, temperature
- Understand the difference betweenmonitoringandcontrolsystems
- Understand the role ofADCandDACin sensor systems
Key Terms
Input Device
Hardware that allows users to pass information from the outside world into a computer system.
Output Device
Any device that takes data stored in digital form and converts it into another form humans can process (sound, images, vibrations).
Sensor
An input device that measures physical properties of the environment and converts them into digital information.
ADC (Analogue-to-Digital Converter)
Converts continuous analogue signals (e.g. from sensors) into discrete digital values a computer can process.
DAC (Digital-to-Analogue Converter)
Converts digital signals into analogue signals needed to drive output devices like motors, valves or speakers.
Monitoring System
Tracks the state of a system, gathers data and may issue warning messages. It has no effect on what is being monitored.
Control System
Controls the system based on input from sensors. It sends signals to actuators to make changes.
Feedback Loop
A process where outputs are recycled and used as inputs, creating a continuous cycle of monitoring and adjustment.
Actuator
A mechanical or electromechanical device that converts an electrical signal into physical movement.
Barcode
A series of dark and light parallel lines of varying thickness representing data. Does NOT contain price.
QR Code
A 2D matrix barcode of black squares on a white background. Can hold over 7,000 digits — much more than a barcode.
Pixel
Picture element — a tiny component that makes up a digital image.
CAD (Computer-Aided Design)
Software used to create precise technical drawings and 3D models, often used as input for 3D printers.
Toner
Fine, dry powder used in laser printers that is fused onto paper using heat.
DLP (Digital Light Processing)
Projector technology using millions of micro-mirrors on a chip to reflect light and create an image.
LCD (Liquid Crystal Display)
Display technology using liquid crystals and a backlight. Used in screens and projectors.
LED (Light-Emitting Diode)
Display technology using tiny light-emitting diodes that produce their own light — no backlighting required.
Additive Manufacturing
Building an object layer by layer (3D printing). Opposite of subtractive manufacturing which removes material.
1. What is an Input Device?
Input devicesare hardware components that allow users to interact with a computer system. They enable the user to input data or commands into the system, which the computer then processes to produce an output.
Real-Life Example
A keyboard is an input device that allows you to type and input information for the computer to understand. A screen is an output device that shows you the information — the output displays the information.
Activity 1: Input or Output?
Classify each of the following devices as an input device, an output device, or both:
- Keyboard
- Monitor
- Microphone
- Touch screen
- Printer
- Speaker
- Webcam
- Headphones
Solution:
- Keyboard —Input
- Monitor —Output
- Microphone —Input
- Touch screen —Both(input and output)
- Printer —Output
- Speaker —Output
- Webcam —Input
- Headphones —Output
Check Your Understanding: Input Devices
1. What is an input device? [2 marks]
- [1]Hardware that allows users to interact with a computer system
- [1]It enables the user to input data or commands into the system
2. Give three examples of input devices. [3 marks]
- [1]Keyboard / mouse / microphone
- [1]Barcode scanner / QR code scanner / digital camera
- [1]Touch screen / 2D or 3D scanner / sensor
3. Give three examples of output devices. [3 marks]
- [1]Monitor / screen
- [1]Printer / 3D printer / projector
- [1]Speaker / headphones / actuator
4. Why is the touch screen considered both an input and output device? [2 marks]
- [1]It displays output (shows options on the screen)
- [1]It receives input (user touches the screen to make a selection)
5. What is the purpose of an output device? [2 marks]
- [1]To take data stored in digital form
- [1]And convert it into another form humans can process (sound, images, vibrations, physical movement)
6. A student says "A game controller is only an input device." Explain why this might not be entirely accurate. [2 marks]
- [1]Modern controllers have built-in speakers and haptic feedback technology
- [1]These make the controller an output device as well (it produces sound and vibrations)
2. Input Devices
The exam board has simplified this section. You only need to knowwhat each device does,why it does it, andwhen it might be used.
Barcode Scanner
What does it do?
It shines a red laser at a barcode to illuminate it. The white lines reflect the light back, whereas the black lines absorb some of the light and reflect less. The strength of the reflection from each line is interpreted by a microprocessor and converted into a binary value.
What is it typically used for?
- Scanning goods at a supermarket checkout
- Checking library books in and out
- Tracking packages out for delivery
Why is it required?
- Faster checkout queues
- Reduces errors caused by manual input
- More detailed tracking information
- Automatic stock control
Digital Camera
What does it do?
As light enters the camera, it falls onto a sensor made up of millions of squares (pixels). Each pixel measures the light intensity, and a microprocessor converts these values into digital data representing colour values.
What is it typically used for?
- Integrated into almost all smartphones
- Professional photography using dedicated, high-end cameras
- Security and surveillance systems
Why is it required?
- Largely replaced traditional, film-based cameras
- Instant photographs — no development required
- Digital photos can easily be transmitted via Wi-Fi, Bluetooth, etc.
- Embedded software can be used to adjust photos — e.g. retouching, filters, red eye removal
Keyboard
What does it do?
Each character on a keyboard has a corresponding character set value. Key presses are converted into a digital signal, which the computer then interprets.
What is it typically used for?
- Connected to most desktop computers via USB connection or wireless/Bluetooth
- Built into laptop computers
- Tablets and smartphones use virtual keyboards
Why is it required?
- One of the most common forms of text-based data input
Optical Mouse
What does it do?
It uses a red LED and a sensor to determine the movement of the mouse relative to the surface beneath. A microprocessor analyses both the speed and distance of the movement and replicates it on-screen via a virtual cursor.
What is it typically used for?
- Navigation and interaction with almost all elements of a graphical user interface (GUI)
Why is it required?
- Easy interaction with applications and other GUI elements
- No moving parts, unlike mechanical mice — more reliable
- No need for a special surface — i.e. a mouse mat
Microphone
What does it do?
Vibrations caused by sound waves cause a coil to move around a magnet, resulting in electromagnetic field changes. These tiny changes are converted by a microprocessor and an analogue-to-digital converter (ADC) into a digital representation of the sound.
What is it typically used for?
- Music recordings, dictation, radio, TV and films
- Telephone calls, security, online communication
Why is it required?
- Capture any real-world sound and store it as a digital approximation
- Digital sounds can then be modified
QR Code Scanner
What does it do?
QR codes are read using a camera, typically on a mobile device. An app then processes the image, converting the squares into readable data.
What is it typically used for?
- Advertising products
- Quick links to websites — no need to type in the URL
- Sharing contact details instantly
- Electronic travel passes, event tickets, etc.
Why is it required?
- Holds far more information than a traditional barcode
- Barcode:30 digits
- QR code:4,296 characters (7,089 digits)
Touch Screen (Resistive, Capacitive and Infra-red)
What does it do?
A touch screen is both an input and output device. Touch screens have become an incredibly popular way of receiving user input, replicating the same functions as a mouse.
Resistive
- Consists of two conductive layers separated by an insulating layer
- The top layer is made of a flexible polyester material
- When the screen is pressed, the two layers contact, completing a circuit
- Used for:Cash machines, information kiosks, medical equipment
- Advantages:Cheap to produce, can be activated with virtually any object, very resistant to surface contaminants
- Disadvantages:Lower image clarity and precision compared to other types
Capacitive
- Composed of a protective layer, transparent conductive layer and a glass substrate
- Touching the screen with a bare finger changes the electrostatic field of the conductive layer
- Used for:Tablets, laptops, smartphones
- Advantages:Excellent image clarity, very high precision, durable, allows multiple touches at the same time
- Disadvantages:Requires a bare finger or capacitive stylus for activation
Infra-red
- LEDs shine infrared light across the screen, forming a matrix
- When the screen is touched, the beams are interrupted
- Used for:Very large-scale commercial displays, information kiosks, medical equipment
- Advantages:Excellent image quality, unlimited touch-life, scales very well
- Disadvantages:Sensitive to interference from ambient light, water, snow, etc.
2D and 3D Scanners
2D Scanner
Shines a bright line across a document to measure the levels of reflected light and create a digital version of it.
Used for:Creating digital versions of documents and photographs, reading passports at airports.
Why required:A simple, cheap and effective way of generating a digital representation of 2D objects for further manipulation.
3D Scanner
Shines a laser over the surface of an object to record its geometry and dimensions and create a digital model of it.
Used for:Creating 3D models for CAD software or 3D printers, dentistry, product development, quality inspection, research.
Why required:Allows the creation of digital models of physical objects for analysis, modification, or reproduction.
Activity 2: Input Devices
- Describe how a barcode scanner reads a barcode. [4]
- Explain the difference between a barcode and a QR code. [3]
- Compare resistive and capacitive touch screens. [4]
- Explain how a 2D scanner works. [3]
Solution:
- Shines light / (red) laser at barcode [1]. Light is reflected back — white lines reflect light, black lines reflect less light [1]. Sensors / photoelectric cells detect the light [1]. Different reflections will give different binary numbers — a microprocessor interprets the data [1].
- Barcode is 1D, QR code is 2D [1]. QR code can hold more data than a barcode [1]. QR code can be read from any angle, barcode readers have to be lined up with barcode [1].
- Resistive uses two conductive layers separated by an insulating layer — pressing the screen completes a circuit [1]. Capacitive uses a conductive layer and glass substrate — touching changes the electrostatic field [1]. Resistive is cheaper but has lower image clarity [1]. Capacitive has excellent image clarity and supports multi-touch [1].
- Sheet of paper is held in a fixed position [1]. Bright light source illuminates the document [1]. A scan head moves from one end of the sheet to the other [1]. Reflected light is directed by mirrors and lenses onto a charge-coupled device (CCD) [1]. Software produces a digital image from the electric form [1].
Check Your Understanding: Input Devices
1. What type of barcode is shown in the image? Explain how the data stored in it is read. [5 marks]
- [1]QR code / Quick Response code
- [1]Read/scanned using an app on a mobile device
- [1]The camera is used to scan/capture the image
- [1]The three large squares are used to define the alignment / uses alignment targets
- [1]Black squares reflect less light / white squares reflect more light / each small square is converted to a binary value
2. Describe how a capacitive touch screen registers a touch. [4 marks]
- [1]Conductive layer
- [1]An electrostatic / electric field is created
- [1]Sensors around the screen monitor the electrostatic field
- [1]When touched, electrostatic charge is transferred to finger / location of touch is calculated
3. Explain how an infrared touch screen detects a user's touch. [4 marks]
- [1]Infrared rays are sent across the screen from the edges
- [1]Sensors around the edge capture the beams
- [1]Infrared rays form a grid across the screen
- [1]Ray is broken by a finger blocking a beam / calculation is made to locate the touch
4. Give two advantages of a QR code over a traditional barcode. [2 marks]
- [1]QR code can hold much more data (over 7,000 digits vs 30 digits)
- [1]QR code can be read from any angle; barcode readers have to be lined up
5. What is the difference between a 2D scanner and a 3D scanner? [2 marks]
- [1]2D scanner captures flat, 2D images of documents or photos
- [1]3D scanner captures detailed 3D shapes and dimensions of objects
6. Explain why an optical mouse is more reliable than a mechanical mouse. [2 marks]
- [1]There are no moving parts
- [1]Dirt can't get trapped in mechanical components / no need for a special surface
3. Output Devices
Anoutput deviceis any device that can take data stored in digital form and convert it into another form humans can process such as sound, images or vibrations.
Actuator
What does it do?
Actuators come in a variety of shapes and sizes. Each version is purpose-built for a specific function, but they essentially all achieve the same goal — to carry out some sort of physical movement.
What is it typically used for?
- Starting and stopping a pump or flow control device
- Opening and closing an automatic door
- Turning a wheel or opening/closing a valve
- Starting and stopping a conveyor belt
- Operating an aircraft's wing flaps
Why is it required?
Actuators are commonly used in conjunction with a motor to translate digital signals into actual, real-world movement of physical objects. They are also often used with sensors to control many kinds of mechanisms.
Digital Light Processing (DLP) Projector
What does it do?
DLP systems use millions of micro-mirrors arranged in a matrix grid and placed on a small microchip within the projector itself. White light is then shone through a rotating colour filter to produce the image, while an angled mirror changes the colour intensity.
What is it typically used for?
- Projecting a computer output onto a wall, whiteboard, projection screen, etc.
- Personal/home and professional settings
Advantages over LCD projectors:
- Higher contrast ratios
- Smoother video
- Smaller, lighter and more portable
- Better suited to dusty or smoky atmospheres
Liquid Crystal Display (LCD) Projector
What does it do?
LCD projectors use three mirror filters to separate an image into its red, green and blue wavelengths. These images are then passed through a prism and recombined. Finally, the full colour image is passed through a lens and projected.
What is it typically used for?
- Projecting a computer output onto a wall, whiteboard, projection screen, etc.
- Personal/home and professional settings
Advantages over DLP projectors:
- Sharper image
- Better colour reproduction
- Typically less expensive
- Quieter operation
- Lower power usage and heat production
Inkjet Printer
What does it do?
Inkjet printers force tiny droplets of liquid ink through very fine nozzles onto a sheet of paper to replicate a digital document or image.
What is it typically used for?
- Mostly used for small-scale print jobs
- Usually cheaper and smaller, so they are popular for personal use
- Excellent for printing out high-quality photos, especially when used with specialist photo paper
Why is it required?
Even now, in this age of technology, there is still a need to produce physical copies of information stored in an electronic format. Printouts or hard copies can be easily transported and viewed at any time without the need for an electronic device or internet connection.
Laser Printer
What does it do?
Laser printers use toner cartridges, which contain powdered, electro-optically charged ink. Using a laser, a mirror image of the printer page is drawn onto a drum by creating negatively charged areas. The drum then picks up the positively charged ink particles and bonds them to the paper using heat.
What is it typically used for?
- High-quality, inexpensive printing
- Very fast and accurate for non-colour documents and images
- Lower running cost per page compared to an inkjet printer
- Often found in schools and offices
Why is it required?
Even now, in this age of technology, there is still a need to produce physical copies of information stored in an electronic format. Printouts or hard copies can be easily transported and viewed at any time without the need for an electronic device or internet connection.
Liquid Crystal Display (LCD) Screen
What does it do?
Liquid crystal displays (LCDs) are made up of millions of tiny liquid crystals. These crystals form a matrix of pixels, which can be affected by changes in applied electric fields. LCD screens require a form of backlighting, often provided by a fluorescent lamp or LEDs.
What is it typically used for?
- TVs, monitors, laptops, mobile devices, etc.
- Gradually being phased out in favour of newer technologies like LED and OLED
Why is it required?
- We need to be able to output digital information in a visual way
- Although display technology is constantly evolving, there will probably always be a need for screens in some form
Light-Emitting Diode (LED) Screen
What does it do?
These displays use tiny light-emitting diodes (LEDs) to produce a bright image almost instantly without the need for any additional backlighting.
What is it typically used for?
- Replacing LCD displays in more and more situations including TVs, monitors, laptops and mobile devices
- Multiple LED screens can be joined together, making them ideal for very large displays used in concerts, festivals and sporting events
Why is it required?
LED technology is generally considered better than LCD because it offers better image quality and viewing angles, has a longer lifespan, and requires no additional backlighting so it's thinner and lighter.
Speaker
What does it do?
Essentially, a speaker is the counterpart to a microphone (an input device) and works in the opposite way. A digital representation of sound is passed through a digital-to-analogue converter (DAC), which can then be further boosted by an amplifier before being passed to a speaker to create analogue sound waves.
What is it typically used for?
- TV, film and video games
- Live music / music recording playback
- Alarms
Why is it required?
Speakers provide us with a way to take digital sounds or recordings and output them in a form that can be heard by the human ear.
3D Printer
What does it do?
Based on inkjet and laser printer technology, 3D printers work by depositing layers of material (often plastic) on top of each other to slowly build a 3D object. They can also use powdered resin or metal, paper, ceramic, concrete — or even certain foods.
What is it typically used for?
- Inexpensive prosthetics / spare parts
- Rapid prototyping
- Personalised items
Why is it required?
3D printing allows us to produce real-world models of virtual objects created using computer-aided design (CAD) software. It can create objects with intricate internal spaces and moving parts, and it provides a means of manufacturing with minimum waste.
Activity 3: Output Devices
- Describe how a DLP projector displays an image. [3]
- Give one advantage and one disadvantage of an inkjet printer compared to a laser printer. [2]
- Explain how a 3D printer creates an object. [3]
Solution:
- Uses a large number of tiny mirrors [1]. Mirrors are laid out in a grid/matrix and each mirror creates a pixel in the image [1]. Mirrors can tilt toward or away from light source, reflecting light toward a projection lens [1]. Colour is produced using a colour wheel / light passes through a colour wheel [1].
- Advantage:Inkjet produces high-quality photo prints / cheaper for home use [1].Disadvantage:Slower for bulk printing / higher running cost per page compared to laser [1].
- A design is made using CAD software [1]. The design is imported into software that prepares it for the 3D printer [1]. The object is built up layer by layer [1]. The object is removed and prepared [1].
Check Your Understanding: Output Devices
1. What is an output device? [2 marks]
- [1]Any device that takes data stored in digital form
- [1]And converts it into another form humans can process (sound, images, vibrations)
2. What is an actuator and where is it used? [3 marks]
- [1]A mechanical or electromechanical device that converts an electrical signal into physical movement
- [1]Used with motors to translate digital signals into real-world movement
- [1]Examples: opening/closing valves or doors, starting/stopping conveyor belts
3. Describe how a DLP projector works. [3 marks]
- [1]Uses millions of micro-mirrors arranged on a small microchip
- [1]White light is shone through a rotating colour filter
- [1]An angled mirror changes the colour intensity / mirrors tilt toward or away from light source
4. Give two advantages of an LED screen over an LCD screen. [2 marks]
- [1]Better image quality and viewing angles
- [1]Requires no additional backlighting, so it's thinner and lighter / has a longer lifespan
5. Explain how a speaker converts digital data into sound. [3 marks]
- [1]Digital data is passed through a DAC (digital-to-analogue converter)
- [1]The signal is boosted by an amplifier
- [1]The electric current drives the speaker, creating sound waves
6. What is the difference between additive and subtractive manufacturing? [2 marks]
- [1]Additive manufacturing builds an object layer by layer (e.g. 3D printing)
- [1]Subtractive manufacturing removes material from a solid block (e.g. carving)
4. Sensors
Sensorsare input devices. They come in different shapes and sizes, but they all measure physical properties of the environment and translate these measurements into digital information that a computer can use.
ADC and DAC
- Analogue-to-Digital Converter (ADC):Converts physical, real-world information (analogue) into discrete digital values.
- Digital-to-Analogue Converter (DAC):Converts digital signals into analogue signals needed to drive output devices like motors, valves or speakers.
Types of Sensors
Temperature Sensor
Measures:Temperature of surroundings or a specific object
Applications:Control of central heating system; monitoring chemical processes; greenhouse temperature control
Moisture Sensor
Measures:Water levels in soil (based on electrical resistance)
Applications:Monitor moisture in soil in a greenhouse; monitor moisture in food processing factory
Humidity Sensor
Measures:Amount of water vapour in air (based on conductivity changes)
Applications:Monitor humidity in buildings; monitor humidity in factory producing microchips; greenhouse humidity control
Light Sensor
Measures:Brightness of light using photoelectric cells
Applications:Switching street lights on/off; automatically switching on car headlights when dark
Infrared Sensor (Active)
Measures:Detects when an invisible beam of infrared radiation is broken
Applications:Security alarm system (intruder breaks beam); automatic windscreen wipers (detects rain)
Infrared Sensor (Passive)
Measures:Heat radiation given off by objects or people
Applications:Security alarm system (detects body heat); monitoring temperature in industrial freezer
Pressure Sensor
Measures:Amount of applied pressure via a transducer
Applications:Weighing lorries at weighing station; measuring gas pressure in nuclear reactor; tyre pressure monitoring
Acoustic / Sound Sensor
Measures:Sound levels (essentially a microphone)
Applications:Security system (footsteps); detect sound of liquids dripping from faulty pipe joint
Gas Sensor
Measures:Presence and levels of gas (e.g. oxygen, carbon dioxide)
Applications:Monitor pollution levels at airport; monitor oxygen/CO2 levels in greenhouse; monitor oxygen levels in car exhaust
pH Sensor
Measures:Acidity through changes in voltages
Applications:Monitor/control acidity levels in soil in greenhouse; control acidity in chemical process
Magnetic Field Sensor
Measures:Changes in magnetic fields
Applications:Anti-lock braking systems in cars; detecting magnetic field changes in mobile phones and metal detectors
Accelerometer
Measures:Acceleration and motion (change in velocity)
Applications:Cars — measure rapid deceleration and apply air bags; mobile phones — change between portrait and landscape mode
Proximity Sensor
Measures:Presence of a nearby object / distance
Applications:Detect when face is close to mobile phone screen; parking sensors; automatic braking systems
Flow Sensor
Measures:Flow rate of a moving liquid or gas
Applications:Respiratory devices and inhalers in hospitals; measure gas flows in pipes
Level Sensor
Measures:Levels of a substance (liquid or powder)
Applications:Monitor petrol levels in a car tank; pharmaceutical process (powder levels in tablet production); leak detection in refrigerant
Monitoring vs Control Systems
Monitoring System
- Sensors record and send signals to a microprocessor
- Signals are converted to digital by an ADC (if required)
- Microprocessor analyses data by checking received values against stored values
- If values are outside the acceptable range, a warning is sent (e.g. on-screen/alarm)
- Microprocessor hasno effecton what is being monitored — it is simply "watching" the process
Control System
- Sensors record and send signals to a microprocessor
- Signals are converted to digital by an ADC (if required)
- Microprocessor analyses data by checking received values against stored values
- If values are outside the acceptable range, a signal is sent to control a valve/motor
- This change (output) affects the following set of input values received from sensors
- This is known as afeedback loop
Activity 4: Sensors & Control
- A security light system is used by a factory. The light only comes on when it is dark and when movement is detected. The light will stay on for 1 minute before switching off. Identify two sensors that would be used. [2]
- Describe how the sensors and the microprocessor control the security light system. [8]
Solution:
- [1]Light sensor.[1]Motion sensor / infrared sensor.
- Any eight from:
- Sensors send data to microprocessor
- Data is converted to digital (using ADC)
- Microprocessor compares data to stored value(s)
- If one value or neither values are within range, no action is taken
- If both values are out of range / in range, microprocessor sends signal to switch light on
- 1-minute timer is started
- Actuator used to switch on/off light
- When timer reaches 1 minute, microprocessor sends signal to switch light off
- Whole process is continuous
Check Your Understanding: Sensors
1. What is a sensor? [2 marks]
- [1]An input device that measures physical properties of the environment
- [1]Converts these measurements into digital information a computer can use
2. What type of sensor would be used to help drivers when reversing? [1 mark]
- [1]Proximity sensor
3. Give one application for each of the following sensors: light, moisture, gas, pH. [4 marks]
- [1]Light — automatically switching street lights on/off depending on light levels
- [1]Moisture — monitoring moisture in soil in a greenhouse
- [1]Gas — monitoring pollution levels in the air at an airport
- [1]pH — monitoring acidity levels in soil for agriculture
4. Explain the difference between a monitoring system and a control system. [3 marks]
- [1]A monitoring system tracks the state of a system and may issue warning messages
- [1]A control system controls the system based on input from sensors
- [1]A control system sends signals to actuators; a monitoring system has no effect on what is being monitored
5. What is the role of an ADC in a sensor system? [2 marks]
- [1]Sensors produce analogue data
- [1]The ADC converts this analogue data into digital data the computer can process
6. Describe how a central heating system uses a temperature sensor and a microprocessor. [5 marks]
- [1]Required temperature is keyed in and stored in microprocessor memory (pre-set value)
- [1]Temperature sensor constantly sends data readings to microprocessor
- [1]Sensor data is first sent to ADC to convert analogue to digital
- [1]Microprocessor compares this data with pre-set value
- [1]If temperature reading < pre-set value, a signal is sent (via DAC) to an actuator to open the gas valve / turn on the water pump
Key Takeaways
- Input devicesallow users to pass information from the outside world into a computer system. Examples: barcode scanner, digital camera, keyboard, microphone, optical mouse, QR code scanner, touch screen, 2D/3D scanners.
- Output devicestake data stored in digital form and convert it into another form humans can process. Examples: actuator, DLP projector, inkjet printer, laser printer, LED screen, LCD projector, LCD screen, speaker, 3D printer.
- Sensorsare input devices that measure physical properties and convert them into digital information.
- ADCconverts analogue signals to digital.DACconverts digital signals to analogue (used to drive actuators, motors, speakers).
- Monitoring systemstrack state and issue warnings but do not control the process.Control systemssend signals to actuators to make changes based on sensor input.
- Feedback loopsoccur when outputs are recycled as inputs, creating a continuous cycle of monitoring and adjustment.
- Barcode scannersuse reflected light to read data — faster checkout, fewer errors, automatic stock control. Barcodes do NOT contain price (it is held on a database).
- QR codesare 2D matrix barcodes that can hold much more data than traditional barcodes and can be read from any angle.
- Touch screenscome in three types: resistive (cheap, any object, lower clarity), capacitive (high precision, multi-touch, needs bare finger), infrared (excellent image, scales well, sensitive to ambient light).
- 2D scannersdigitise documents and photos.3D scannerscapture the geometry and dimensions of solid objects to create 3D models.
- DLP projectorsuse millions of micro-mirrors.LCD projectorsuse three mirror filters and a prism. Each has advantages and disadvantages.
- Inkjet printersuse liquid ink through fine nozzles (good for photos).Laser printersuse toner and heat (fast, high-volume, low cost per page).
- LED screensproduce their own light (no backlighting) — thinner, lighter, better image quality than LCD.
- 3D printersbuild objects layer by layer (additive manufacturing) using plastic, resin, metal, etc.
- Actuatorsconvert electrical signals into physical movement — used with motors and sensors to control mechanisms.
Question Bank
1. Describe how a barcode scanner reads a barcode. [4 marks]
- [1]Shines light / (red) laser at barcode
- [1]Light is reflected back — white lines reflect light, black lines reflect less light
- [1]Sensors / photoelectric cells detect the light
- [1]Different reflections give different binary values — a microprocessor interprets the data
2. Explain how an infrared touch screen detects a user's touch. [4 marks]
- [1]Infrared rays are sent across the screen from the edges
- [1]Sensors around the edge capture the beams
- [1]Infrared rays form a grid across the screen
- [1]Ray is broken by a finger blocking a beam — calculation is made to locate the touch
3. Compare barcodes and QR codes. [4 marks]
- [1]Barcode is 1D; QR code is 2D
- [1]Barcodes contain vertical lines; QR codes contain squares
- [1]QR code can hold more data than a barcode (7,089 digits vs 30 digits)
- [1]QR code can be read from any angle; barcode readers have to be lined up with barcode
4. Describe how a DLP projector displays an image. [3 marks]
- [1]Uses a large number of tiny mirrors
- [1]Mirrors are laid out in a grid/matrix — each mirror creates a pixel in the image
- [1]Mirrors can tilt toward or away from light source — reflecting light toward a projection lens / colour is produced using a colour wheel
5. Give two advantages of an LED screen over an LCD screen. [2 marks]
- [1]Better image quality and viewing angles
- [1]Requires no additional backlighting, so it's thinner and lighter / has a longer lifespan
6. Explain how a 3D printer creates an object. [4 marks]
- [1]A design is made using computer-aided design (CAD) software
- [1]The drawing is imported into software that prepares it for the 3D printer
- [1]The object is built up layer by layer
- [1]The object is removed from the printer and prepared (e.g. support material washed away)
7. A security light system is used by a factory. The light only comes on when it is dark and when movement is detected. Identify two sensors that would be used and describe how the sensors and microprocessor control the system. [8 marks]
- Sensors [2]:Light sensor [1] and motion/infrared sensor [1]
- [1]Sensors send data to microprocessor
- [1]Data is converted to digital using ADC
- [1]Microprocessor compares data to stored value(s)
- [1]If one value or neither values are within range, no action is taken
- [1]If both values are out of range/in range, microprocessor sends signal to switch light on
- [1]1-minute timer is started
- [1]Actuator used to switch on/off light
- [1]When timer reaches 1 minute, microprocessor sends signal to switch light off / process is continuous
8. Explain how a capacitive touch screen registers a touch. [4 marks]
- [1]Conductive layer
- [1]An electrostatic / electric field is created
- [1]Sensors around the screen monitor the electrostatic field
- [1]When touched, electrostatic charge is transferred to finger / location of touch is calculated
9. What is the difference between a monitoring system and a control system? [3 marks]
- [1]A monitoring system tracks the state of a system and may issue warning messages
- [1]A control system controls the system based on input from sensors
- [1]A control system sends signals to actuators; a monitoring system has no effect on what is being monitored
10. Describe how a laser printer produces a printed page. [4 marks]
- [1]A laser draws a mirror image of the page onto a drum by creating negatively charged areas
- [1]The drum picks up positively charged toner (powdered ink)
- [1]The toner is transferred to the paper
- [1]Heat and pressure fuse the toner permanently onto the paper
11. Give three examples of input devices and three examples of output devices. [6 marks]
Input devices (any 3):
- [1]Keyboard / mouse / microphone
- [1]Barcode scanner / QR code scanner / digital camera
- [1]Touch screen / 2D or 3D scanner / sensor
Output devices (any 3):
- [1]Monitor / screen
- [1]Printer / 3D printer / projector
- [1]Speaker / headphones / actuator
12. Explain how a 2D scanner works. [4 marks]
- [1]Sheet of paper is held in a fixed position
- [1]Bright light source illuminates the document
- [1]A scan head moves from one end of the sheet to the other / reflected light is directed by mirrors and lenses onto a charge-coupled device (CCD)
- [1]Software produces a digital image from the electric form
13. State what is meant by an actuator and give one example of its use. [2 marks]
- [1]A mechanical or electromechanical device that converts an electrical signal into physical movement
- [1]Example: opening/closing a valve or door, starting/stopping a conveyor belt, operating an aircraft's wing flaps
14. What type of sensor would be used in each of these applications? (a) Weighing a baby in hospital (b) Turning off a kettle when it boils (c) Controlling an automatic door (d) Monitoring air quality in an aeroplane (e) Counting cars crossing a bridge. [5 marks]
- [1](a) Pressure sensor
- [1](b) Temperature sensor
- [1](c) Infrared / light / pressure / proximity sensor
- [1](d) Gas / humidity sensor
- [1](e) Pressure / infrared / magnetic field sensor
15. Compare resistive and capacitive touch screens. Give one advantage and one disadvantage of each. [4 marks]
- Resistive [2]:Uses two conductive layers separated by an insulating layer — pressing the screen completes a circuit [1]. Advantage: cheap to produce, can be activated with virtually any object [1]. Disadvantage: lower image clarity and precision [1].
- Capacitive [2]:Uses a conductive layer and glass substrate — touching changes the electrostatic field [1]. Advantage: excellent image clarity, high precision, supports multi-touch [1]. Disadvantage: requires a bare finger or capacitive stylus [1].