Design & Technology (AS/A‑Level) – Materials, Components and Control Systems
1. The Design Process (8‑stage model)
- Identify the need – research the problem and write a clear design brief.
- Analyse the brief – list constraints (cost, safety, sustainability, performance, regulatory).
- Generate ideas – sketch, mind‑map or use digital tools to produce a range of concepts.
- Develop a solution – select the most promising idea and create detailed drawings, CAD models and functional specifications.
- Plan – produce a work‑plan, risk assessment and bill of materials (BOM).
- Make – fabricate, assemble and test the prototype.
- Evaluate – compare the outcome with the brief, record improvements and any failures.
- Iterate – refine the design or move to production.
Case study (smart thermostat): the electronic control system (temperature sensor, micro‑controller, driver transistor, relay) is developed during stages 3–7.
2. Design Principles – “Good Design” Criteria
| Criterion | Key considerations for electronic/control products |
|---|
| Functionality | Reliability of sensing, processing and actuation; correct voltage/current ratings; clear signal flow. |
| Ergonomics | Button size, spacing, travel, tactile feedback; readability of displays; hand‑size suitability. |
| Usability | Intuitive control logic, clear symbols, minimal user steps, logical sequencing. |
| Aesthetics | Colour, finish, integration of LEDs or indicators, visual hierarchy. |
| Safety | Isolation, fusing, protective enclosures, compliance with IEC/BS standards, emergency shut‑off. |
| Sustainability | Low‑power design, recyclable components, avoidance of hazardous substances (RoHS), design for disassembly. |
| Manufacturability | Standard component footprints, PCB panelisation, ease of assembly, tolerance to production variation. |
| Cost | Component price, assembly time, warranty considerations, total cost of ownership. |
3. Communication in Design
- Free‑hand sketching – use consistent line‑weights, hidden lines (dashed), dimension arrows and annotation.
- Orthographic views – front, side and top projections at the same scale; include section cuts where needed.
- CAD tools – block‑diagram software (Lucidchart, draw.io) for functional schematics; PCB design packages (EAGLE, KiCad) for layout.
- Schematic conventions – IEC symbols, junction dots, net labels, reference designators (R1, C2, Q3, U1, etc.).
Mini‑exercise: Write a brief for a “Portable USB‑powered fan”, draw a 2‑D schematic and a simple PCB layout using a CAD tool.
4. Technology in Society
Electronic control systems underpin modern life – from household appliances to transport. Key societal issues include:
- E‑waste – rapid product turnover creates landfill challenges; design for disassembly and recycling mitigates impact.
- Data privacy & security – connected control units must protect user data and resist unauthorised access.
- Energy consumption – standby (vampire) loads add to national demand; low‑power design and automatic shut‑off reduce waste.
5. Sustainable Design Checklist for Electronic Products
- Choose components with low embodied energy (lead‑free solder, recycled copper, high‑efficiency ICs).
- Design for energy efficiency – use sleep modes, PWM control, and high‑efficiency drivers.
- Minimise material use – compact PCB, multi‑function ICs rather than many discrete parts.
- Enable repairability – socketed ICs, modular connectors, clear labelling of parts.
- Plan end‑of‑life – provide recycling information, avoid hazardous substances, use biodegradable packaging where possible.
6. Health & Safety for Electronics Workshops
| Hazard | Control measures (PPE, practice) |
|---|
| Soldering iron (≥350 °C) | Heat‑resistant gloves, safety glasses, fume extraction, stand‑by holder. |
| Live circuits (≤240 V AC / 12 V DC) | Insulated tools, disconnect power before testing, use a residual‑current device (RCD). |
| Sharp components (pins, PCB edges) | Safety glasses, finger guards, store components in labelled containers. |
| Chemical exposure (flux, cleaning solvents) | Ventilated area, nitrile gloves, proper waste disposal. |
| Noise (drilling, cutting) | Ear protection, low‑speed operation where possible. |
7. Aesthetics & Ergonomics for Hand‑held Electronic Devices
- Overall size < 100 mm × 60 mm × 20 mm for comfortable one‑hand use.
- Button travel 1–2 mm, tactile feedback, minimum centre‑to‑centre spacing 6 mm to avoid accidental presses.
- Surface finish – matte or textured to reduce glare and improve grip.
- Visual hierarchy – LEDs or icons placed where the eye naturally falls; use colour contrast for status indication.
8. Materials & Components
8.1 Materials Covered in the Syllabus
| Material Group | Typical Uses in Control Systems |
|---|
| Metals (steel, aluminium, copper) | Enclosures, heat sinks, conductors, PCB tracks, mechanical fasteners. |
| Polymers (ABS, PC, PETG) | Case mouldings, cable insulation, 3‑D printed prototypes, snap‑fit housings. |
| Composites (fibreglass, carbon fibre) | Lightweight structural parts, high‑strength brackets, vibration‑damped mounts. |
| Smart & Modern Materials | Conductive inks, flexible PCBs, shape‑memory alloys for actuators, piezoelectric ceramics. |
| Biodegradable options | PLA for rapid prototyping, compostable packaging, bio‑based resins. |
| Traditional materials (wood, paper, glass) | Prototype housings, documentation, optical sensor windows. |
8.2 Stages in Materials Processing (Syllabus Requirement)
- Measuring & Marking – use calipers, rulers, laser guides, or CAD‑generated templates.
- Cutting – hand saws, band saws, laser cutters, water‑jet, CNC milling.
- Shaping/Forming – drilling, milling, turning, bending, stamping, injection moulding, 3‑D printing.
- Joining – soldering, brazing, welding, adhesive bonding, mechanical fasteners, snap‑fit design.
- Finishing – sanding, polishing, coating (paint, anodising, powder coat), surface texturing, heat‑treatment.
8.3 Common Processing Techniques (Hand & CNC)
| Technique | Typical Equipment | Materials Best Suited |
|---|
| Hand sawing / coping | Hacksaw, coping saw | Wood, low‑thickness plastics, thin metal sheets. |
| Laser cutting | CO₂ or fibre laser cutter | ABS, acrylic, plywood, thin steel. |
| Water‑jet cutting | High‑pressure abrasive jet | Thick metal, composites, ceramics. |
| CNC milling | 5‑axis or 3‑axis milling centre | Aluminium, brass, plastics, PCB material. |
| 3‑D printing (FDM) | Desktop or industrial FDM printer | PLA, PETG, ABS, flexible TPU. |
| Injection moulding | Industrial moulding machine | Thermoplastics (PC, ABS, polycarbonate). |
| Brazing / soldering | Torch, soldering iron, reflow oven | Metals for electrical joints, PCB assembly. |
| Adhesive bonding | Epoxy, cyanoacrylate, structural adhesives | Dissimilar materials, composites. |
| Powder coating | Electrostatic spray booth, curing oven | Aluminium, steel enclosures. |
8.4 Electronic Components – Function and IEC Symbol
| IEC Symbol | Component (Reference Designator) | Typical Function in a Control System |
|---|
⎯⎯⎯⎯⎯⎯
⎯⎯⎯⎯⎯⎯ | Resistor (R) | Sets current, forms voltage dividers, biasing networks. |
| || | Capacitor (C) | Energy storage, filtering, timing (RC networks). |
⎕⎕⎕
⎕⎕⎕ | Inductor (L) | Filters, energy storage in switching regulators. |
| →| | Diode (D) | Rectification, reverse‑polarity protection. |
| →|⦿ | LED (D1) | Visual status indicator, user feedback. |
⎕
│
▲ | BJT NPN (Q) | Switching or amplification of control signals. |
⎕
│
▼ | BJT PNP (Q) | Complementary switching in H‑bridge circuits. |
| ⎕—⎕ (gate) | MOSFET (Q) | Low‑loss switching, PWM motor control. |
| ⎕—⎕ (coil) | Relay coil (K) | Electromechanical actuation of high‑current loads. |
| ⎕—⎕ (contacts) | Relay contacts (K‑NO / K‑NC) | Open/close power to motors, solenoids, heaters. |
| ⎕—⎕ (switch) | Push‑button / toggle (S) | User input, start‑stop control. |
| ⎕—⎕ (arrow) | Potentiometer (POT) | Adjustable voltage divider for set‑point tuning. |
| ⎕—⎕ (T) | Thermistor (RT) | Temperature sensing for thermostatic control. |
| ⎕—⎕ (←) | Photodiode (PD) | Light‑level detection, safety interlocks. |
| ⎕—⎕ (M) | DC Motor (M) | Actuator delivering mechanical work. |
| ⎕—⎕ (S) | Solenoid (SOL) | Linear actuation (valve, latch). |
| IC | Integrated Circuit (U) | Microcontroller, comparator, driver – core processing. |
8.5 Symbol Construction Rules (IEC‑standard)
- Draw on a 1 mm grid; centre symbols on grid lines.
- Line thickness: 0.5 mm for primary lines, 0.25 mm for secondary details (e.g., diode arrows).
- Component values and reference designators are placed immediately to the right of the symbol (e.g.,
R1 = 10 kΩ).
- Polarity marks (+ / – , cathode bar) are mandatory for electrolytic capacitors, diodes, LEDs, and polarized ICs.
- Connections: solid lines; a filled dot denotes a junction, an open circle denotes a wire crossing without connection.
- Orientation: pins numbered clockwise for ICs; collector‑base‑emitter order for BJTs; arrow direction indicates current flow for diodes and MOSFETs.
9. Energy & Control Systems (Syllabus Topic)
9.1 Energy Sources and Forms
- Fossil‑based – mains AC, batteries (alkaline, lead‑acid).
- Renewable – solar PV panels, wind generators, thermoelectric generators.
- Mechanical – springs, flywheels, human‑powered cranks.
- Thermal – heat‑pipes, thermoelectric coolers.
9.2 Energy Conversion & Transmission
| Conversion | Typical Device | Control‑system Relevance |
|---|
| Electrical → Mechanical | DC motor, stepper motor, servo | Actuation of fans, pumps, valves. |
| Mechanical → Electrical | Generator, dyno, piezoelectric sensor | Energy harvesting, speed feedback. |
| Thermal → Electrical | Thermoelectric (Seebeck) module | Temperature‑driven power for low‑energy sensors. |
| Electrical → Light | LED, laser diode | Indicators, optical communication. |
| Light → Electrical | Photodiode, photovoltaic cell | Ambient‑light sensing, solar charging. |
9.3 Simple Control Strategies
- On/Off (binary) control – comparator or thermostat triggers a relay.
- PWM (Pulse‑Width Modulation) – varies duty cycle to control motor speed or LED brightness.
- Closed‑loop (feedback) control – sensor → controller (microcontroller or analog comparator) → actuator; e.g., PID temperature regulation.
- Safety interlocks – limit switches, light curtains, emergency stop circuits.
10. Example Control Circuit – Temperature‑Controlled Fan
Purpose: Automatically switch a 12 V DC fan on when ambient temperature exceeds a user‑set set‑point.
10.1 Key Components
- Thermistor (RT) – forms a voltage divider with a fixed resistor.
- Operational Amplifier (U1) configured as a comparator.
- Potentiometer (POT) – provides the reference voltage for the comparator.
- Relay (K1) – coil driven by the comparator output; contacts switch the fan.
- Flyback diode (D1, 1N4007) across the relay coil.
- Fuse (F1, 2 A fast‑acting) for supply protection.
- 12 V regulated DC supply.
10.2 Schematic (textual description)
- Thermistor (RT) and a 10 kΩ resistor are wired in series between +12 V and 0 V. The junction feeds the non‑inverting (+) input of U1.
- The inverting (–) input receives the reference voltage from a 5 kΩ potentiometer wired as a voltage divider.
- U1’s output drives the relay coil (K1). When the thermistor voltage exceeds the reference, the output goes high, energising the coil.
- Relay contacts (normally open) are placed in series with the fan motor and the +12 V line.
- D1 is installed cathode‑to‑+12 V across the coil to clamp inductive spikes.
- F1 protects the entire circuit from over‑current.
10.3 Design Considerations (linked to “Good Design” criteria)
- Functionality: Precise set‑point via POT; reliable mechanical relay for high‑current switching.
- Safety: Fuse, flyback diode, insulated wiring, clear labelling of high‑voltage points.
- Sustainability: Low‑power comparator (<1 mA standby); relay only energised when needed.
- Ergonomics: External adjustment knob for POT; LED indicator (D1) shows “fan on”.
- Manufacturability: All parts on a standard 0.1 in (2.54 mm) PCB grid; through‑hole components for easy hand‑assembly.
11. Summary – What Students Must Know
- The eight‑stage design process and its link to the stages in materials processing.
- Good‑design criteria and how to evaluate a control system against them.
- Effective communication: free‑hand sketches, orthographic projections, IEC schematic symbols, and basic CAD output.
- Societal and environmental impacts of electronic products (e‑waste, data security, energy use).
- Health & safety practices specific to soldering, live circuits, chemicals and workshop noise.
- Aesthetic and ergonomic considerations for handheld or portable devices.
- Full range of materials listed in the syllabus and the relevant processing stages and techniques.
- Functions and IEC symbols of the most common electronic components used in control circuits.
- Construction rules that ensure clear, unambiguous schematics.
- Energy sources, forms, conversion methods and simple control strategies required by the “Energy & Control Systems” topic.
- How to assemble a real‑world control circuit (temperature‑controlled fan) and justify design choices using the criteria above.