All Systems Go

This physics extension module from the Salters' Science course deals with binary digital electronic devices, taking a systems approach. Ideas of input, output and control are considered and the concept of feedback. The use of logic gates to control switches and latches is studied and relays are explored as a way of switching larger currents.

Lesson 1: Making sense of systems
Common features of various systems are identified. Students make and modify a light-controlled electronic system to operate a variety of output devices.

Lesson 2: Highs and lows
Students build systems using a variety of sensors and outputs. Some systems include inverters. Signals are described as ‘high’ or ‘low’. They use LEDs as indicators and explore the properties of diodes.

Lesson 3: Decisions
Students use 2-input logic gates (OR, NOR, AND and NAND gates) to build systems which respond to more than one input. They use truth tables to describe the action of components and systems. The action of relay switches in controlling large currents is illustrated.

Lesson 4: Finding out about transistors
Students are introduced to simple transistor circuits. They see that transistors can be used as electrically controlled switches to control other components.

Lesson 5: Staying on
A bistable latch and a combination of logic gates are used to make a timing system. Students explore ways of controlling bistable devices and consider their importance in various contexts, including computer memory circuits.

Lesson 6: Delaying the action
Students investigate the action of an RC delay circuit. The action of capacitors is explained in terms of storage and flow of charge.