What is a System?

A system is made up of a number of units which have been linked up to serve some useful purpose. A complete system can:

  • accept inputs, in the form of signals or materials,
  • carry out some process upon them,
  • produce desired output.

A system will respond in a predictable way when it receives suitable signals, or materials, at its input. Systems can be divided up into three sections. These are shown here:

Block diagram of a system

Some systems have several inputs and outputs.


Let’s consider a washing machine as an example of a system. Inputs would include:

Inputs of a Washing Machine

The control panel switches are set by the user according to the type of wash to be carried out.

The processing block makes decisions based upon the state of the inputs. Provided it is supplied with water and electricity the processing section would:

  • open water valve and fill tank
  • heat the water
  • wash the clothes
  • empty water
  • spin dry the clothes
  • switch off

The output of a washing machine would be clean clothes and dirty water.

You will probably be able to think of many more examples of systems that you come across in everyday life and identify their input, processing and output.

Electronic Systems

This is a simple block diagram representing an electronic system

An electronic system

Input Transducers, often referred to as sensors, convert external signals e.g. a change in light intensity, into an electrical form.

Output Transducers convert electrical signal into some other form. These include buzzers, LEDs and relays. A relay is used as a switching device if the output transducer requires more current than can be provided by a digital IC package. You will be investigating the use of a transistor to interface between IC packages and output transducers requiring high current.