Systems: Materials, Sources and Properties
Welcome to your study notes for Systems: Materials, sources and properties! In Pearson Edexcel GCSE (9-1) Design and Technology, "Systems" focuses on electronic and programmable systems that sense the world, make decisions, and create useful outputs like sound, light, and movement. Don't worry if electronics feels technical at first—we will break down every single component, its physical properties, and how it works step by step.
Note: Detailed stock forms, tolerances, and circuit calculations are explored in separate chapters; this chapter focuses squarely on identifying components, understanding their operational properties, and examining their origins and environmental impacts.
---1. The Building Blocks: Input, Process, Output
Every electronic system follows an essential three-stage model: Input \(\rightarrow\) Process \(\rightarrow\) Output.
Think of it like human reflexes:
• Input (Sensing): Your eyes see a ball flying towards you.
• Process (Deciding): Your brain decides to put your hands up to catch it.
• Output (Action): Your arm muscles move your hands into position.
In electronic systems, we use physical components to carry out each of these three roles.
---2. Input Devices: Sensors and Switches
Sensors detect changes in the physical environment and convert them into an electrical signal (a change in voltage or current). Switches allow human users or physical mechanisms to manually open or close an electrical pathway.
A. Sensors
• Light-Dependent Resistor (LDR): A sensor whose resistance changes depending on ambient light levels. In the dark, an LDR has very high resistance. As light intensity increases, its electrical resistance decreases. LDRs are commonly used in automatic night lights and street lighting.
• Thermistor: A temperature-dependent sensor. In typical negative temperature coefficient (NTC) thermistors, resistance decreases as the temperature increases. They are used in digital thermometers, car engine cooling systems, and central heating controls.
• Moisture Sensor: Consists of conductive probes placed in a material (such as soil). When moisture is present, water conducts electricity between the probes, lowering resistance. As the material dries out, resistance rises. These are widely used in automated plant-watering systems.
B. Switches
• Push-to-Make Switch (PTM): A momentary switch that only completes a circuit when pressed down. The moment you release it, the connection breaks. Example: A doorbell button.
• Rocker Switch: A latching switch that rocks back and forth between two fixed positions ("on" and "off"). It stays in position until switched again. Example: The main power switch on a desktop fan.
• Micro Switch: A very sensitive switch requiring very little physical force to trigger. Often fitted with an actuator lever or roller. Example: Detecting whether a microwave door or printer access panel is completely shut.
• Reed Switch: An enclosed glass switch with two thin, magnetic metal reeds. When an external magnet comes close, the magnetic field pulls the contacts together, completing the circuit. Example: Burglar alarms on windows and doors (a magnet on the moving window frame triggers the switch on the frame).
Key Takeaway for Inputs: Sensors (LDR, thermistor, moisture sensor) automatically respond to physical variables like light, heat, and moisture. Switches (rocker, PTM, micro, reed) open or close circuits via human touch, physical mechanisms, or magnetic fields.
---3. Control and Processing Devices
Processing devices take signals from inputs, manipulate them, or use them to make logical decisions before sending signals to the outputs.
A. Passive Control Components
• Resistors (Fixed): Components that oppose and limit the flow of electric current in a circuit. They protect delicate parts (such as LEDs) from burning out due to excessive current.
• Variable Resistors: Resistors whose resistance can be adjusted manually (like a dial or slider). They are used to tune circuits, such as adjusting the volume on a sound system or calibrating sensor thresholds.
B. Active Switching and Amplifying Devices
• Bipolar Transistor: A semiconductor component that can act as an electronic switch or an amplifier. A very small input current at the base pin can switch on a much larger current between the collector and emitter pins. This allows tiny sensor signals to control larger components.
• Relay: An electromechanical switch that uses an electromagnet to physically pull contact points closed. Relays allow a low-voltage, low-power electronic circuit (such as a 5V microcontroller) to safely switch a high-voltage, high-current circuit (such as a 230V mains electric heater) with complete electrical isolation between the two.
C. Programmable Processing Units
• Microprocessor: An integrated circuit containing the central processing unit (CPU) only. It requires external chips for memory (RAM/ROM) and input/output control to function. Microprocessors handle heavy processing tasks.
• Microcontroller / PIC (Peripheral Interface Controller): A complete "mini-computer on a single chip". It includes the processor core, memory, and programmable input/output pins all built into one package. Microcontrollers can be programmed using flowcharts or written code to read inputs, execute delays, loops, and decisions, and control outputs directly. They are common in washing machines, automotive controllers, and microwave ovens.
Key Takeaway for Processors: Resistors manage current; transistors amplify or switch small currents; relays use magnetism to switch high-power circuits safely; and microcontrollers/PICs provide programmable, intelligent decision-making on a single chip.
---4. Output Devices
Output devices convert electrical energy back into real-world phenomena: light, sound, or physical motion.
• Buzzer: An audio signalling device that produces a buzzing or beeping tone at a single fixed frequency. Buzzers are ideal for alarms, timers, and warning alerts where high fidelity is not needed.
• Light-Emitting Diode (LED): A semiconductor light source that emits light when current flows through it in the forward direction. LEDs are highly energy-efficient, generate minimal heat, turn on instantly, and have an extremely long lifespan compared to traditional incandescent filament lamps. They are widely used for indicator lights, displays, and domestic lighting.
• Loudspeaker: An electroacoustic transducer that converts varying electrical audio signals into sound waves across a wide range of frequencies (speech, music, multi-tone alerts) by vibrating a flexible diaphragm using an internal voice coil and permanent magnet.
• Motor (DC Electric Motor): An actuator that converts electrical energy into continuous rotary kinetic energy. Motors power wheels, cooling fans, drills, and conveyor belts.
Key Takeaway for Outputs: Buzzers provide fixed warning tones; loudspeakers reproduce complex sound; LEDs provide efficient, directional light; and motors generate rotary physical movement.
---5. Working Properties of Systems Materials
The components used in electronic systems depend heavily on distinct physical and electrical properties:
• Electrical Conductivity: The ability of a material to let electrical charge flow freely through it. Copper is the primary conductor used for component legs, wires, and printed circuit board (PCB) tracks due to its high conductivity and low resistance.
• Electrical Insulation: Materials that prevent current flow. Polymers (like PVC on wire sleeving and FR4 epoxy glass boards) keep conductors separated, preventing short circuits and protecting users from electric shocks.
• Semiconductor Properties: Materials (chiefly silicon) that sit between conductors and insulators. By chemically treating silicon, engineers create diodes, transistors, LEDs, and integrated circuits (microcontrollers) that control, direct, or amplify current.
• Magnetic Properties: Utilised in components like relays, loudspeakers, and motors, where electromagnetic fields interact with permanent magnets or ferrous armatures to create physical movement.
6. Sources, Origins, and Environmental Footprint
The materials that make up electronic systems come with important ecological and social considerations that designers must evaluate:
A. Raw Material Extraction and Processing
• Semiconductors and Metals: Silicon is processed from quartz sand using high-temperature, energy-intensive furnaces. Precious and base metals—including copper (for wiring and PCB tracks), gold (for corrosion-resistant microchip bond wires), and rare-earth elements (neodymium for loudspeaker and motor magnets)—require open-pit mining and complex chemical purification.
• Polymers: Resins and plastics used for component encapsulation, switch casings, and wire insulation are primarily derived from crude oil refining.
B. Ecological and Social Footprint
• Habitat Destruction and Pollution: Mining ores consumes substantial energy and water, generating toxic mine tailings and chemical pollutants if not strictly managed.
• E-Waste (Electronic Waste): Discarded electronic products present a major disposal challenge. Many electronic components are soldered permanently onto circuit boards, making separation and recycling difficult and labour-intensive.
• Toxicity in Landfill: Discarded systems containing heavy metals or flame-retardant plastics can leach hazardous substances into groundwater if sent to landfill rather than dedicated electronic waste recovery facilities.
• Resource Depletion: Many specialty metals used in microchips and motors have limited global reserves, driving the need for modular designs that permit easy repair, reuse, and recycling.
7. Quick Review: Component Matching Summary
Check your understanding with this summary of the core systems components:
• Light-Dependent Resistor (LDR): Resistance drops as light levels rise (Input).
• Thermistor: Resistance drops as temperature rises (Input).
• Moisture Sensor: Conducts electricity across probes when wet (Input).
• Reed Switch: Contacts close when exposed to a magnetic field (Input).
• Micro Switch: Triggered mechanically with light physical force (Input).
• Fixed / Variable Resistors: Limit or adjust current flow (Control/Process).
• Bipolar Transistor: Electronic switch or amplifier (Control/Process).
• Relay: Electromechanical switch isolating low-power inputs from high-power loads (Control/Process).
• Microcontroller / PIC: Programmable single-chip computer running logical routines (Control/Process).
• Buzzer / Loudspeaker: Convert electrical signals to sound (Output).
• LED: Converts electrical current directly to light efficiently (Output).
• Motor: Converts electrical current into continuous rotary motion (Output).