Electronics and control systems
Design & Technology · Key Stage 3 · The School
Input, process, output
Every control system has the same three stages. INPUT senses something — a switch, a light sensor, a thermistor for temperature, a moisture sensor. PROCESS decides what to do about it. OUTPUT acts — a lamp, a buzzer, a motor, a heater. Describing an unfamiliar product in those three stages is the fastest way to work out how it functions.
Choosing components
Components are chosen by what they must sense or do. A thermistor changes resistance with temperature and suits a heating control; a light-dependent resistor suits a street lamp; a motor suits movement and a solenoid a short push. A resistor in series with an LED is not optional — without it the LED draws too much current and fails.
Microcontrollers
A MICROCONTROLLER is a small programmable computer that performs the process stage. Instead of fixed circuitry deciding the behaviour, a program does — so the same hardware can be changed by rewriting code rather than rewiring. That is why a modern product can be improved after it is built, and why so much of D&T now involves programming.
A microcontroller with a temperature sensor and a relay. PROGRAM 1: if temp < 18 turn the relay on — you have a thermostat. PROGRAM 2: if temp > 40 turn the relay on and sound a buzzer — you have a fire alarm. Identical hardware, identical wiring, two different products, and the change took thirty seconds. That is what programmability buys, and why rewiring is not the alternative.