Systems: The sources, origins, physical and working properties of components and systems and their social and ecological footprint

Overview

In GCSE Design and Technology, understanding systems is about recognising how individual components work together to sense the environment, process information, and produce a response. This topic (5.2) covers not only the technical function of these components but also the physical properties of the materials used to house them, and critically, the global social and ecological footprint of their production and disposal.

Key Knowledge & Theory

The Systems Approach

Almost all electronic systems can be broken down into three stages:

1. Input: Where information or energy enters the system, typically via a sensor.
2. Process: Where the input signal is evaluated or modified, typically by a control device.
3. Output: Where the system responds with a physical action, light, or sound.

Core Components

Input Devices (Sensors)

• Light Dependent Resistor (LDR): A sensor whose resistance decreases as light intensity increases. Used in automatic street lighting and camera exposure controls.
• Thermistor: A temperature-sensitive resistor. Most are Negative Temperature Coefficient (NTC), meaning resistance decreases as temperature rises. Used in central heating thermostats and digital thermometers.
• Moisture Sensor: Detects the presence of water by completing a circuit between two conductive probes. Used in automated irrigation systems.
• Piezoelectric Sensor: Generates a small electrical voltage when physically deformed or subjected to vibration. Used in knock sensors and electronic drum pads.

Process/Control Devices

• Transistor: A solid-state semiconductor device used to amplify or switch electrical signals and power. A small current at the base terminal controls a much larger current between the collector and emitter.
• Relay: An electromechanical switch. A low-power signal energises an electromagnet, which pulls a physical contact to close a separate, high-power circuit. Essential for safety when interfacing low-voltage logic with mains electricity.
• Microprocessor: A programmable integrated circuit that acts as the 'brain' of a system, executing stored instructions to process inputs and control outputs.
• Resistor: A component designed to introduce a specific amount of resistance into a circuit, limiting current flow or dividing voltage. Resistance is calculated using Ohm's Law (V = I \times R).

Output Devices

• Light Emitting Diode (LED): A highly efficient semiconductor light source that emits light when current flows through it in the forward direction.
• Buzzer: An audio signalling device that converts an electrical signal into sound.
• Motor: Converts electrical energy into rotational mechanical energy.
• Loudspeaker: Converts electrical audio signals into corresponding sound waves by moving a cone.

Material Properties for Enclosures

When designing a product, the housing must protect the electronics and the user.

• Polymers (e.g., ABS): Chosen for their toughness, durability, ease of injection moulding into complex shapes, and excellent electrical insulation properties.
• Metals (e.g., Aluminium): Used for heat sinks due to high thermal conductivity, drawing heat away from sensitive components like microprocessors.

Social and Ecological Footprint

The creation and disposal of electronic components have profound global impacts. Examiners expect candidates to discuss these issues with specific examples.

Raw Material Extraction

• Cobalt: Essential for lithium-ion batteries. Approximately 60% is mined in the Democratic Republic of Congo (DRC), often involving hazardous working conditions, child labour, and significant environmental degradation (Social and Ecological impact).
• Lithium: Extracted from salt flats in South America (Chile, Argentina). The process is highly water-intensive, threatening local ecosystems and indigenous water supplies (Ecological and Social impact).
• Tantalum: Derived from coltan, mined in Central Africa. Historically linked to funding armed conflict, earning it the label of a "conflict mineral" (Social impact).
• Silicon: The foundation of microchips. While silica is abundant, the purification process requires massive amounts of energy, contributing to greenhouse gas emissions if powered by fossil fuels (Ecological impact).

End of Life and Legislation

• Built-in Obsolescence: Designing products with an artificially limited useful life to encourage repeat purchases. This drives up resource consumption and waste generation.
• WEEE Directive (Waste Electrical and Electronic Equipment): European legislation requiring manufacturers to take responsibility for the collection, treatment, and recycling of e-waste to divert toxic materials (like heavy metals) from landfill.
• RoHS Directive (Restriction of Hazardous Substances): Legislation restricting the use of specific hazardous materials (like lead and mercury) in the manufacture of electronic and electrical equipment.

Audio Revision

Listen to this 16-minute revision podcast covering all the key concepts, exam tips, and a quick-fire recall quiz.