Chapter 3: Hardware

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1. Logic Gates & Circuits

Theory:

• Logic Gates: Electronic circuits performing Boolean operations (AND, OR, NOT, etc.).
• AND (A·B): Output 1 only if all inputs are 1.
• XOR (A⊕B): Output 1 if inputs differ.
• NAND (A·B): Output 0 only if all inputs are 1.
• Circuit Design:
• Brackets dictate operation order (e.g., NOT (A OR B) vs. NOT A OR B).
• Use gate symbols systematically (e.g., OR gate → NOT gate = NOR).

Past Paper Example (2023 Q5a):
Question: Draw the circuit for X = NOT (A OR B OR C) OR (B AND C AND D).
Marking Scheme Answer:

1. First segment: A OR B OR C → 3-input OR gate → NOT gate.
2. Second segment: B AND C AND D → 3-input AND gate.
3. Final output: Combine both segments with OR gate.
   Common Errors:

• Misplacing NOT gate (e.g., applying NOT to individual inputs).
• Incorrect gate symbols (e.g., using XOR instead of OR).

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2. Embedded Systems

Theory:

• Definition: A specialized computer system (e.g., washing machine) with:
• Dedicated function: Optimized for specific tasks.
• Real-time operation: Responds instantly to inputs.
• RAM vs. ROM:
• RAM: Stores temporary data (e.g., sensor readings). Volatile.
• ROM: Stores firmware (e.g., boot code). Non-volatile.

Past Paper Example (2022 Q5c):
Question: Explain why a refrigerator’s temperature system is a control (not monitoring) system.
Marking Scheme Answer:

• Control systems act on input data (e.g., turn cooling on/off).
• Monitoring systems only display data (e.g., temperature readout).
• Key phrase: “The fridge’s microprocessor adjusts the cooling, making it a control system.”

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3. Storage Devices

Theory:

• Magnetic Hard Disks:
• Platters: Rotating disks with magnetic coating.
• Read/write heads: Alter magnetic fields to store data.
• Advantages: Low cost per GB, high capacity.
• SSDs:
• NAND flash memory: No moving parts; faster access.
• Wear leveling: Extends lifespan by distributing writes.

Past Paper Example (2023 Q4b):
Question: Compare DRAM and SRAM for a CCTV system.
Marking Scheme Answer:

DRAM	SRAM
Cheaper; used for main memory (high density).	Faster; used for cache (lower latency).
Requires refreshing; higher power use.	No refresh; lower power use.

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4. Input/Output Devices

Theory:

• Microphones:
• Operation: Sound waves → diaphragm vibration → coil movement in magnetic field → electrical signal → ADC → digital data.
• Resistive Touchscreens:
• Layers: Two conductive layers separated by spacers.
• Pressure: Completes circuit to register touch.

Past Paper Example (2021 Q8a):
Question: Describe how a microphone works.
Marking Scheme Answer:

1. Sound waves hit the diaphragm, causing vibrations.
2. Vibrations move a coil within a magnetic field, generating an electrical current.
3. Current is converted to digital via ADC.
   Key Terms: Diaphragm, coil, ADC.

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5. Networks & Communication

Theory:

• Router Functions:

1. DHCP: Assigns IP addresses to devices.
2. NAT: Translates private IPs to public IPs.
3. Firewall: Blocks unauthorized access.

• Star Topology:
• Central switch: Directs traffic to devices.
• Advantages: No collisions; fault isolation.

Past Paper Example (2022 Q8b):
Question: Identify three router functions in a home network.
Marking Scheme Answer:

1. Assigns IP addresses via DHCP.
2. Routes data between devices and the internet.
3. Provides wireless access (WAP).

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6. Monitoring & Control Systems

Theory:

• Feedback Loops:
• Example: Thermostat compares actual temperature to target → adjusts heating.
• Sensors vs. Actuators:
• Sensor: Measures data (e.g., temperature sensor).
• Actuator: Executes action (e.g., fan motor).

Past Paper Example (2024 Q10a):
Question: Why is feedback critical in a greenhouse window system?
Marking Scheme Answer:

• Ensures windows adjust automatically to maintain optimal conditions (e.g., temperature, humidity).
• Prevents overheating or excessive cooling.

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Key Definitions (Marking Scheme Buzzwords)

• Embedded System: “A dedicated computer system with a specific function, often real-time and low-power.”
• Logic Gate: “An electronic circuit implementing a Boolean function (e.g., AND, OR).”
• DRAM: “Volatile memory requiring refresh cycles; used for main memory due to high density.”

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Common Pitfalls & How to Avoid Them

1. Logic Circuits:

• Error: Misinterpreting NOT A OR B as NOT (A OR B).
• Fix: Use brackets to clarify operation order.

1. RAM vs. ROM:

• Error: Stating “ROM stores temporary data.”
• Fix: ROM is non-volatile (permanent).

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Worked Example (2024 Q7a)

Question: Complete the truth table for X = (A NAND B) OR (A AND NOT C).

A	B	C	NOT C	A NAND B	A AND NOT C	X
0	0	0	1	1	0	1
0	1	1	0	1	0	1
1	1	0	1	0	1	1

Marking Scheme Tips:

• Intermediate columns (e.g., NOT C) often earn partial marks.
• Final output (X) must match all input combinations.

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