📟 Why Input Devices?
Input devices convert real‑world commands and data into digital signals that a
computer can process.
Essential for all computer systems, from desktops to specialized equipment.
Common everyday devices: mouse and keyboard.
Specialist devices include scanners, sensors, barcode readers, QR‑code
scanners, etc.
📠 Most Important Input Devices
Barcode scanner
Keyboard (physical & virtual)
Optical mouse (wired or wireless)
Microphone
Digital camera
QR‑code scanner
Touch screen (resistive, capacitive, infrared)
2D and 3D scanners
🏷️ Barcode Scanner
Barcode – a pattern of black and white bars representing encoded data.
How a Barcode Reader Works
1. Emit a red laser onto the barcode.
2. Reflect light: white bars return more light; black bars absorb it.
3. Detect reflected light with photo‑electric cells.
4. Convert light‑intensity levels into binary values (e.g., L = 0, D = 1).
Binary Conversion Example
Bar pattern
Binary (L = 0, D = 1)
LDDDDLD
0111101
Stock Control in Supermarkets (POS)
1. Scan the product’s barcode at checkout.
2. Reader sends the product code to the inventory database.
3. Database deducts one unit from stock.
4. System alerts staff when stock falls below a threshold.
Advantages to Management
Rapid price updates – change once in the system.
Real‑time sales data – instantly identifies trends and best‑sellers.
No manual labeling – saves staff time and reduces errors.
Automatic stock alerts – prevents out‑of‑stock situations.
Customer‑behavior analytics – link purchases to loyalty cards.
Advantages to Customers
Faster checkout – scanning is quicker than manual entry.
Fewer pricing errors – prices come directly from the system.
Itemised receipts – clear view of purchased items.
Potential cost savings – efficiency can lower prices.
Improved freshness – better rotation via expiry‑date tracking.
🔲 QR Codes
QR (Quick Response) code – a square matrix of light/dark pixels that can store up to
4 296 alphanumeric characters.
How QR Codes Work
1. Open a QR‑reading app on a smartphone or tablet.
2. Point the camera at the code.
3. The app captures the image and decodes the pixel pattern.
4. The decoded data triggers the appropriate action (open URL, display contact,
etc.).
Common Uses
Advertising products.
Direct links to websites or phone numbers.
Electronic boarding passes.
Advantages Over Barcodes
Much larger data capacity (thousands of characters).
Built‑in error correction – readable even when partially damaged.
Easy to read with any smartphone camera, no special scanner needed.
Shareable as images or text messages.
Encryptable for added security.
Disadvantages
Multiple QR‑code formats → not all scanners support every type.
Malicious codes can lead to phishing or malware.
Professional creation tools (especially for branded “frame” QR codes) may be
costly.
Festival Organizer Applications
QR‑encoded e‑tickets for entry scanning.
QR‑based advertising on flyers and posters.
Links to the festival website or schedule.
On‑site information (maps, performer bios) accessed via QR scans.
📸 Digital Camera
Digital camera – an input device that captures light and converts it directly into digital
image data.
Operation Steps
1. Light passes through the lens onto a sensor (CCD or CMOS).
2. The sensor converts light photons into electrical charges.
3. An ADC (Analog‑to‑Digital Converter) translates these charges into digital
pixel values.
4. Pixels store RGB colour information (8 bits per channel, 24‑bit colour).
Key Components
Component
Function
CCD / CMOS sensor
Transforms light into electric charge
ADC
Converts charge to digital numbers
Pixel (picture element)
Individual colour sample (RGB)
Typical Use Cases
Promotional business cards with FrameQR® graphics.
Authenticity verification (combining QR with holograms).
Discount labels using QR + OCR for extra data.
⌨️ Keyboard
Keyboard – the primary device for entering text‑based data, using physical keys or
virtual on‑screen keys.
Connected via USB or wireless (Bluetooth, RF).
Physical keys: each key has a contact peg that presses a membrane,
generating a unique electrical code.
Keyboard Types
Standard – flat layout, may cause awkward wrist angles.
Ergonomic (split) – promotes natural hand, wrist, and forearm positions,
reducing RSI risk.
Ergonomic Benefits
Encourages a neutral wrist angle.
Decreases repetitive‑strain injuries.
Can improve overall typing comfort and productivity.
🎙️ Microphone
Microphone – an input device that transforms acoustic sound waves into electrical
signals.
How It Works
1. Sound waves move the diaphragm.
2. Diaphragm motion induces an electrical current in a nearby coil.
3. The analog signal is digitised by an ADC and processed by a microprocessor.
Common Applications
Music recording.
Telephone and VoIP calls.
Online communication and dictation.
🖱️ Optical Mouse
Optical mouse – a pointing device that tracks movement using light rather than a
mechanical ball.
Operation Steps
1. A red LED illuminates the surface.
2. A CMOS sensor captures ~1500 images per second.
3. A DSP (Digital Signal Processor) compares successive images to calculate
displacement.
4. The cursor moves accordingly.
Advantages Over Mechanical Mice
No moving parts → works on most surfaces, no dirt buildup.
Higher reliability and precision.
Wired Mouse Advantages
No signal loss – constant wired connection.
Cost‑effective – no batteries or charging required.
Environmentally friendly – no disposable batteries.
📊 2D & 3D Scanners
2D scanner – captures flat documents by projecting a light strip and measuring
reflected intensity for each pixel.
3D scanner – captures the shape of an object to create a three‑dimensional digital
model.
2D Scanning Process
1. Light strip sweeps across the document.
2. Reflected light is measured (often via CCD sensors).
3. Data is converted to binary pixel values.
4. OCR software can transform scanned text into editable files.
3D Scanning Uses
CAD model creation.
Rapid prototyping with 3D printers.
Dental and medical imaging (bones, teeth, organs).
Cultural heritage preservation (artifacts, archaeology).
Application Summary
Application
Document archiving
OCR text extraction
Medical imaging (CT, MRI)
Product design / reverse
engineering
Entertainment (games,
animation)
Security (passport
scanning)
2D Scanner
3D Scanner
✅ (barcode/QR)
✅
✅ (character/face
capture)
✅
✅
✅
✅
✅
❌
❌
✅
✅
🖐️ Touchscreen
Touchscreen – a combined input and output device that registers user contact and
displays visual feedback.
Types Overview
Type
How It Works
Advantages
Disadvantages
Typical Uses
Capacitive
Finger (or
Clear images,
Surface type
special stylus)
sunlight
needs bare
changes
readability,
finger or
electrostatic scratch‑resistant, compatible
field;
stylus; can
supports
microcontroller
suffer EM
multi‑touch
interference.
reads X‑Y
(projective).
coordinates.
Smartphones,
tablets, kiosks.
Infrared
Grid of IR
Multi‑touch,
emitters/sensors; durable, not
touch blocks
affected by
beams,
cracks,
allowing
long‑term
coordinate
reliability.
calculation.
Large public
displays, ATMs.
Resistive
Two flexible
Works with No multi‑touch, Cash machines,
layers pressed finger, stylus, poorer visibility
industrial
together;
terminals,
gloves; dust‑
in sunlight,
voltage change
medical
and
requires firm
detected as water‑resistant. press, prone to
equipment.
touch.
scratches.
Sensitive to
moisture,
accidental
beam
interruptions,
strong light
interference.
Example Exam Questions
Describe how a resistive touch screen works.
State one advantage of a capacitive screen over a resistive screen.
Why are touch screens considered I/O devices?
📋 Quick Cheat Sheet of Input Devices
Device
How It Works
Benefits /
Drawbacks
Typical Uses
Resistive
touchscreen
Two layers contact
→ voltage change
+ Works with
gloves, stylus<br>−
ATMs, industrial
panels
No multi‑touch,
lower brightness
Infrared
touchscreen
IR beams broken by
touch
+ Multi‑touch,
durable<br>−
Sensitive to
moisture, false
touches
Large kiosks, public
info screens
Capacitive
touchscreen
Finger alters
electrostatic field
+ Excellent clarity,
multi‑touch<br>−
Requires
conductive touch
Smartphones,
tablets
Barcode scanner
Laser reads
reflectivity → binary
code
+ Fast checkout,
error
reduction<br>−
Limited data
capacity
Retail POS, parcel
tracking
QR‑code scanner
Camera captures
matrix → decode
data
+ Large data, error
correction, easy to
read<br>− Format
incompatibility,
security risk
Advertising, tickets,
product info
2D/3D scanner
Light strip / laser
maps surface →
digital model
+ Quick digitisation,
OCR possible<br>−
Requires good
lighting, may be
costly
Document
archiving, CAD,
medical imaging
Digital camera
Lens → sensor
(CCD/CMOS) →
ADC → digital
image
+ Instant preview,
high
resolution<br>−
Storage needed
Photography,
security,
smartphones
Keyboard
Key press →
membrane contact
→ electrical code
+ Universal text
entry, low
cost<br>− Can
cause RSI (if
non‑ergonomic)
Data entry,
programming
Microphone
Diaphragm → coil →
electrical signal →
+ Captures audio
for many
Recording, calls,
voice commands
ADC
applications<br>−
Sensitive to
background noise
Optical mouse
LED + sensor tracks
surface movement
+ No moving parts,
works on many
surfaces<br>−
Needs power
(batteries for
wireless)
GUI navigation,
gaming
Wired mouse
Direct electrical
connection to PC
+ No signal loss, no
batteries,
cheap<br>− Less
portable than
wireless
Desktop
workstations