GCSE Design & Technology: Electronics and Programmable Components Revision Guide

Basic components

Electronic circuits are built from basic components, each with a specific job. A resistor limits or controls the flow of electric current in a circuit, and is commonly placed in series with a light emitting diode (LED) to prevent too much current flowing and damaging it. An LED only allows current to flow in one direction and emits light when current passes through it, making it useful as an indicator. A switch opens or closes a circuit to control whether current can flow. Input components can also respond to their environment: a thermistor changes resistance with temperature, and a light dependent resistor (LDR) changes resistance depending on the amount of light falling on it — both are commonly used as sensors.

Circuits

Components can be connected in series or in parallel. In a series circuit, components are connected one after another along a single path, so if one component fails or is removed, the whole circuit stops working because there is no alternative route for the current. In a parallel circuit, each component (or branch) has its own separate path back to the power supply, so if one component fails, current can still flow through the other branches, meaning the rest of the circuit continues to work.

Systems: inputs, processes and outputs

Electronic products can be thought of as systems made up of inputs, processes and outputs. Inputs are components that sense a change or receive information, such as a push switch, an LDR or a thermistor. Processes take the information from the inputs and decide what should happen, which is often carried out by a microcontroller running a program. Outputs are components that do something as a result, such as a motor, a buzzer, a heater or an LED. A security light system, for example, might use a PIR (passive infrared) sensor as an input to detect movement, a microcontroller as the process to decide whether it is dark enough and movement has occurred, and a lamp as the output.

Microcontrollers and programmable components

A microcontroller is a small programmable chip that can read signals from input components, follow a set of instructions (a program), and control output components accordingly. Because the behaviour of a microcontroller is controlled by software rather than fixed wiring, designers can change how a product behaves simply by rewriting the program, without needing to redesign the physical circuit. This makes programmable components extremely flexible and is why they are widely used in modern smart products, from washing machines to wearable devices.

Common mistakes

• Confusing series and parallel circuits — remember that in a series circuit a single break stops everything, while in a parallel circuit other branches can keep working.
• Forgetting to include a resistor with an LED, which can lead to the LED being damaged by too much current in both real circuits and exam circuit diagrams.
• Mixing up inputs and outputs in a systems diagram — sensors and switches are inputs, while motors, lamps and buzzers are outputs.