Chapter 2 Notes: Input and Output Devices (2.1–2.3)
2.1 Input devices and their uses
Keyboards
- The most common method for data entry; used as input on computers, tablets, mobile phones, etc.
- Connections: USB or wireless; on tablets/phones, keyboards are often virtual or touchscreen-based.
- When a key is pressed, it is converted into a digital signal that the computer interprets.
- Relative drawbacks: keyboards are slow compared with some data-entry methods and prone to errors.
- However, keyboards are probably the easiest way to enter text into a computer.
- For prolonged use, frequent use can lead to injuries (e.g., repetitive strain injury, RSI).
- Ergonomic keyboards exist to mitigate RSI: keys arranged differently and greater wrist/hand support when typing.
- How a letter press is recognised (summary of Fig. 2.3):
- There is a membrane or circuit board under the keys.
- Pressing a key (e.g., ‘H’) completes a circuit.
- The CPU identifies the key pressed and refers to an index file to map the key press to the character.
- Uses of keyboards:
- Input data into applications (e.g., text into word processors).
- Typing commands (e.g., PrtScn, Ctrl+P to print).
- Advantages:
- Fast entry of new text; widely understood; easy verification (compare source with on-screen text).
- Disadvantages:
- Can be difficult for users with limited arm/wrist use.
- Slower than direct data entry (e.g., scanner).
- Takes up desk space.
Numeric Keypads
- Specialised input for numbers; some have a function key for alphabetic input.
- Uses:
- ATMs (PIN entry, amounts).
- Mobile phones (phone numbers).
- POS terminals (manual entry if barcode read fails).
- Chip & PIN devices (PIN, amount).
- Fast numeric data entry in spreadsheets.
- Advantages:
- Faster than a standard keyboard for numeric data.
- Small size makes them easy to carry.
- Disadvantages:
- Small keys can be hard to press accurately.
- The numeric arrangement may not be intuitive on all keypads.
Pointing devices
Mouse
User moves the pointer by moving the mouse; usually two buttons (left for selection/double-click, right for menus).
Some have a scroll wheel to move through documents quickly.
Optical mice and cordless/motionless (wireless) mice have no moving parts and resist dirt better; older mice can skid on certain surfaces.
Uses of a mouse:
Open/close/minimise software; group, move, delete files; image editing (size/position of images); select items from menus or icons; scrolling.
Advantages:
Faster than using a keyboard for many tasks; quick navigation of applications and the internet; requires less desk space than a keyboard.
Touchpad / Trackpad
Built into many laptops; pointer controlled by finger movement on the touchpad; tapping simulates the left mouse button; some laptops have physical buttons under the touchpad.
Uses: same as a mouse (control pointer, select items).
Advantages: integrated into laptops; good portability (no separate mouse needed).
Disadvantages: harder for some users with limited hand/wrist movement; pointer control may be less precise than a mouse.
Trackball (Tracker Ball)
- A ball on the device is rotated to move the pointer; some have two or three buttons (third button can simulate a double-click).
- Advantages: good for users with limited wrist movement; smaller desk footprint; often faster for certain tasks.
- Uses: alternative to a mouse in RSI contexts; navigation in control rooms; sometimes used in luxury cars for function control.
- Disadvantages: not usually included with the computer by default and may require training.
Remote control
- Used to operate other devices via infrared signals; buttons select functions.
- Uses: televisions, satellite systems, DVD/Blu-ray players, Hi-Fi systems; control multimedia systems; remote industrial control.
- Advantages: can be operated from a distance; useful in hazardous industrial contexts.
- Disadvantages: difficult for users with limited hand/wrist movement; signal can be blocked by thick walls or obstacles.
Joysticks & driving wheels
- Joystick: functions similar to a mouse/trackerball; moving the stick controls a screen pointer; game/purpose-built buttons.
- Uses: video/computer games; simulators (e.g., flight simulators) to mimic real controls.
- Advantages: easier than a keyboard for navigation; more realistic control for some applications.
- Disadvantages: harder to control the on-screen pointer than with a mouse.
- Driving wheel: USB connection; simulates turning a steering wheel; includes pedals and additional controls; sensors detect movement for realistic steering feel.
- Uses: car racing games; car-driving simulators.
- Advantages: steering feels more natural; closer to real-life operation.
- Disadvantages: expensive; steering movements can be overly sensitive; limited tactile feedback unless high-end hardware.
Touch Screen (input device)
- User selects options by touching a button/icon on the screen; no separate pointing device required.
- Uses:
- Self-service kiosks (petrol stations) for selecting fuel grade and payment.
- ATMs for on-screen options.
- POS terminals in restaurants.
- Public information systems (airports, railway stations, tourist offices).
- Mobile phones, tablets, satellite navigation.
- Interactive whiteboards in education.
- Computer-based training (CBT) for on-screen responses.
- Also acts as an output device when displaying information.
- Advantages:
- Faster option entry than keyboard/mouse; very easy to use; user-friendly; can expand display size if needed.
- Disadvantages:
- Limited input options; reduced effectiveness for large data input/output tasks; can get dirty and be less responsive in bright sunlight.
2.2 Direct Data Entry (DDE) devices
Direct Data Entry devices operate with minimal human interaction; data transfer to the computer happens automatically.
Card readers (Magnetic stripe readers)
- Read information on the magnetic stripe on the back of cards (account number, sort code, expiry, start date, etc.).
- Uses:
- Credit/debit card transactions at ATMs or EFTPOS terminals.
- Security doors/rooms; hotel rooms; etc.
- Advantages:
- Fast data entry; error-free as no typing is required; secure; robust (no moving parts; oil/water resistant).
- Disadvantages:
- If the stripe is damaged, data is lost; does not work at a distance (card must be in contact with reader); information is not human-readable, which can be a disadvantage in some contexts.
Contactless Debit Card Readers
- Use radio-frequency to enable payment without PIN entry; chip inside emits radio waves.
- Advantages:
- Faster transactions; 128-bit encryption enhances security; customer avoids PIN errors; retailers do not access card data.
- Disadvantages:
- More expensive hardware; risk of interception by a nearby reader; potential for double charges if a card is used both contactless and chip-and-PIN; limits on transaction amounts; some risk of silent transactions without the card holder’s awareness.
'Chip' & PIN Reader
- Similar to smart card readers but used at EFTPOS; card is inserted and the chip is read.
- Customer enters PIN; RF not used.
- Uses: payments at points of sale (restaurants, supermarkets, travel agents, etc.).
- Advantages: more secure than magnetic stripe; PIN verification stored on chip provides robustness.
- Disadvantages: risk of PIN being observed by others while entered.
Radio Frequency Identification (RFID) readers
- Use radio waves to read and capture information stored on a tag.
- Components: a microchip and an antenna; tags can be battery-powered (active) or passive.
- Battery-powered tags have a small embedded battery; passive tags rely on reader’s radio waves to power and relay information.
- Uses:
- LIVESTOCK tracking, retail (store items), admission passes, libraries, etc.
- Advantages:
- No line-of-sight required; read at distance; robust and fast read rate (< 100 milliseconds to respond); bidirectional data transfer; bulk detection possible (multiple tags at once).
- Disadvantages:
- Tag collision when signals from multiple tags interfere; easier to jam or intercept signals; can be hacked; generally more expensive than barcode systems.
Optical Mark Recognition (OMR)
- Reads marks/shading on forms (e.g., questionnaires, multiple-choice exams, voting papers).
- Advantages:
- Very fast data input; high accuracy due to lack of typing; more accurate than OCR for forms.
- Disadvantages:
- Forms must be carefully designed for correct shading; incorrect filling requires manual checking (time and cost).
Optical Character Recognition (OCR)
- Converts images of text into editable text files.
- Uses:
- Processing passports/identity cards; converting hard copy documents to electronic form; automatic number plate recognition (ANPR); digitising historic newspapers/books.
- Advantages:
- Faster data entry; fewer typing errors when converting documents.
- Disadvantages:
- Handwriting recognition is imperfect; not always highly accurate; handwriting variability can cause errors.
OCR vs OMR (Table 2.2 summary)
- OCR reads handwritten or printed text and converts to editable text; vulnerability to handwriting quality; complex recognition required; more versatile for varied documents.
- OMR reads marks on a form according to a template; ideal for multiple-choice exams; highly accurate for well-designed forms but requires complex forms and templates; usually faster for that narrow task.
Barcode Reader / Scanner
- Barcode is a numeric code represented as a series of lines; readers are often built into POS terminals.
- Uses:
- Supermarkets and shops; product information and automatic stock control; libraries for loan tracking; safety checks on equipment.
- Advantages:
- Much faster than keyboard data entry; reduces mistakes; aids stock control and safety testing; proven technology.
- Disadvantages:
- Relatively expensive to administer; barcodes can be swapped; damaged barcodes are problematic.
Quick Response (QR) Codes
- QR is a code comprising a block of small squares (pixels); large corner squares provide alignment; the code contains data and can be scanned by cameras.
- Holds more information than normal barcodes; normal barcodes hold up to about 30 digits; QR codes can hold significantly more (over digits).
- Uses:
- Advertising with data (addresses, phone numbers, emails, websites); links to apps; storing Wi‑Fi authentication details; delivering augmented reality experiences; virtual stores.
- Advantages:
- Higher data capacity; built-in error checking; easier to read with cameras; encryptible; easy to transmit as text or image.
- Disadvantages:
- Multiple QR formats exist; risk of malicious QR codes (attagging); free apps can generate codes; scanning could lead to malware if scanned from untrusted sources.
2.3 Output devices and their uses
CRT (Cathode Ray Tube) Monitor
- Low-cost monitor technology; image made up of red/green/blue phosphor dots; brightness determined by dot intensity.
- Uses:
- CAD/CAM work in specialist areas; large screens for complex diagrams; used with light pens for on-screen design.
- Advantages:
- Wide viewing angles; compatible with light pens for CAD/CAM.
- Disadvantages:
- Heavy; runs hot; high power consumption; prone to flicker causing headaches over long use; potential weight hazards if not supported properly.
LED/LCD screens
- LED: backlighting via LEDs; LEDs are RGB; very bright and energy-efficient; used in large outdoor displays; OLED variants exist.
- LCD: uses liquid crystals; backlit (usually by LEDs); combined with thin panels; modern LCDs are backlit by LEDs and are not pure LED displays.
- Why LEDs for backlighting are popular:
- Immediate maximum brightness; whiter light improves perceived image quality; thinner and lighter panels; long life; low power consumption.
- Uses of LCD screens:
- Main output device for most modern computers; many offer touch input; used in phones, tablets, laptops, portable gaming.
- Advantages of LCDs:
- Very efficient, low power; lightweight; no image burn-in like CRTs; large variation in sizes; no flicker; sharp image resolution; low electromagnetic emissions.
- Disadvantages of LCDs:
- Color/contrast can vary with viewing angle; motion blur; lower contrast than CRTs; possible pixel issues (dead/stuck pixels); uneven backlight illumination across the panel.
Touch Screen (as output device)
- Acts as both input and output device when used for interaction with apps.
- Uses:
- Smartphones/tablets; ATMs (on-screen outputs depend on previous input); ticket kiosks; museums and information kiosks.
- Advantages:
- Quick option entry; user-friendly; can zoom or expand the display as needed.
- Disadvantages:
- Limited data output/input capacity for large data sets; less precise for lengthy data entry; screen cleanliness affects usability.
Multimedia Projector
- Accepts analogue/digital signals; typically from computer, TV, or DVD player; magnifies and projects onto a large screen.
- Often used with a remote or cordless PC mouse with a laser pointer for navigation.
- Formats: PAL, NTSC, SECAM.
- Uses:
- Training presentations; advertising at exhibitions; home cinema systems.
- Advantages:
- Enables many people to view content simultaneously; avoids multiple networked computers.
- Disadvantages:
- Images can be fuzzy; expensive to buy; setup can be challenging.
Laser Printer
- Produces high-quality output; high-speed for large print runs; relies on large buffer memories to collect document data before printing.
- Uses:
- Environments needing low noise (offices); fast, high-quality, high-volume printing.
- Advantages:
- Fast printing for large volumes; high-quality output; long-lasting toner cartridges; cost-effective if colour output is not required.
- Disadvantages:
- Expensive to buy; fastest only with large print runs; colour laser printers are expensive to run due to multiple toner cartridges and diffusers.
InkJet Printer
- Lacks large buffer memory; prints in small portions as data arrives; components include: print head with nozzles, color cartridges (cyan, magenta, yellow) and black; motion system (stepper motor and belt); automatic paper feed.
- Two printing technologies:
- Thermal bubble: heat causes ink to vaporize, forming a bubble that ejects ink; when bubble collapses, ink refills; cycle repeats.
- Piezoelectric: a crystal in the nozzle vibrates when charged, ejecting ink and drawing more ink for subsequent printing.
- Uses:
- Suited for low-output volumes; high-quality single-page prints; modern 3D inkjet printers are used for prototyping in industry.
- Advantages:
- High-quality output; cheaper to buy than laser printers for some uses; lightweight with small footprint; does not emit ozone or VOCs like some lasers.
- Disadvantages:
- Slow for multiple copies; not ideal for high-volume printing; ink can smudge if handled carelessly; ink cartridges can be expensive.
Dot Matrix Printer
- Impact printer using a print head (matrix of pins) striking an inked ribbon.
- Uses:
- Environments that are noisy or dirty; multi-part stationery or continuous paper (carbon copies); receipts in retail environments.
- Advantages:
- Tolerates dusty, damp, or dirty environments; suitable for continuous multi-part outputs; cheap to run for long print jobs.
- Disadvantages:
- Very noisy; slower and lower quality than inkjet/laser; higher purchase cost than inkjets; poorer print quality.
Plotter
- Uses a pen/pencil/marker to draw continuous lines (vectors) rather than dot-based printing; supports large paper sizes (from A4 to several metres).
- Produces vector graphics; often used with CAD/CAM.
- Uses:
- Architectural drawings; engineering drawings; drawing animation characters.
- Advantages:
- Very high-quality output; can print large monochrome or color drawings with high accuracy; works on a variety of materials (aluminium, cardboard, plastic, steel, wood, and paper).
- Disadvantages:
- Very slow; expensive to buy upfront; large physical footprint.
3D Printers
- Used in CAD applications to produce solid objects built layer by layer (additive manufacturing).
- Materials include powdered resin, powdered metal, paper, or ceramic; closely tied to inkjet/laser printing technologies.
- Some features:
- Various sizes from microwave-sized to car-sized machines.
- Direct 3D printing uses a print head that moves in X and Y and also up/down to form layers; Binder 3D printing uses two passes per layer (powder + binder).
- Newer methods use lasers or UV light to harden liquid polymers.
- Uses:
- Prosthetic limbs customized to fit a body part; precise surgical aids (facial reconstruction); aerospace parts with lightness and precision; fashion and art; replacement parts for discontinued items.
- How to create a solid object:
- Design in CAD; export to a printer-friendly format; set up the 3D printer; build object layer by layer (often ~ per layer);
- removal of supports and post-processing; curing if required.
- Advantages:
- Customisation; rapid prototyping; cost savings over traditional manufacturing; medical benefits (prosthetics, reconstructive aids); replacements for discontinued parts.
- Disadvantages:
- Counterfeiting/copyright concerns; potential misuse for dangerous items; possible impact on jobs in traditional manufacturing.
Speaker output devices
- Convert digital audio to sound via a chain: Digital data → DAC (digital-to-analogue converter) → amplifier → loudspeaker.
- When an electric current through a coil near a permanent magnet varies, the iron core is attracted/repelled; attached to a cone, this vibration produces sound.
- Uses:
- Built into most computers and used in multimedia presentations; helps visually impaired people by reading text aloud with accompanying software; plays downloaded sound files.
- Advantages:
- Amplified sound can be much louder than the original; facilitates group listening; adds atmosphere to presentations; assists visually impaired users.
- Disadvantages:
- Can disturb others in office environments; high-quality speakers can be expensive; occupy desk space.
Actuators
- Used to control devices (motors, pumps, switches, valves) by converting electrical signals into mechanical motion.
- Examples: relays, solenoids, motors.
- E.g., a solenoid converts an electrical signal into a magnetic field producing linear motion: a plunger inside the coil moves when current is applied, enabling a valve or switch to operate; rotary solenoids produce rotational movement.
- Uses:
- Control motors, pumps, switches, buzzers, and other devices; enable computers to control physical processes that require analogue inputs.
- Advantages:
- Enable remote operation of many devices (important for safety in hazardous environments like nuclear reactors); relatively inexpensive.
- Disadvantages:
- Add another component that can fail; most are analogue, requiring a DAC to interface with digital systems.
Sensors (analogue sensors; ADC required to convert to digital data)
- A sensor inputs data to a computer as a measurement of a physical quantity that changes continuously; computers operate on digital data (1s and 0s).
- ADC (Analogue-to-Digital Converter) is required to convert sensor data to digital form.
- Uses: monitoring and control applications; data often transferred to spreadsheet packages for analysis (e.g., scientific measurements, environmental monitoring).
- Table 2.1 (Types and applications):
- Temperature sensors: automatic washing machines, central heating, automatic glasshouses, ovens.
- Pressure sensors: intruder alarms, washing machines, robotics, environmental monitoring.
- Light sensors: automatic glasshouses, automatic doors, intruder alarms, street lighting control.
- Sound/acoustic sensors: intruder alarms, monitoring liquid/powder flow in pipes.
- Humidity/moisture sensors: glasshouses, environmental monitoring, manufacturing (e.g., microchips, paint spraying).
- pH sensors: automatic glasshouses, environmental monitoring, chemical processes.
Light pens
- Input devices that rely on light detection; work with CRT monitors (not LCDs in this stage of development).
- How they work: light pen detects when the screen’s electron beam passes the pen tip; the display refresh rate (e.g., 50 Hz) allows accurate position detection.
- Uses:
- Selecting objects on CRT screens; on-screen drawing (e.g., CAD).
- Advantages: higher accuracy than touch screens; compact; easy to use.
- Disadvantages: lag during drawing; limited to CRT displays; not very accurate for freehand drawing; somewhat dated technology.
2.3 Output devices and their uses (continued)
2.2 Direct Data Entry (DDE) devices (summary)
2.2 Direct Data Entry (DDE) devices (summary, continued)
Light pen, OCR/OMR, RFID, magnetic stripe, QR, barcode, etc. (summary)
Overall note: DDE and output devices complement input methods by enabling automatic transfer, high-speed data capture, and clear, scalable output for diverse applications.