Electronic systems consist of:

· An input device to sense changes, e.g. a light detector

· A processor that responds to the change

· An output device that enables the system to do something useful.

· There may be feedback to control the response of the circuit.

We can represent this very basic idea with a block diagram:

Now try Question 1, Question 2, and Question 3.

Circuit diagram tells us:

· How the components are laid out and wired up.

· Engineers use circuit diagrams to assemble the circuit.

· It uses standard symbols with which you need to be familiar.

· The lines represent the copper tracks on the circuit board. Where the lines are connected there is a black dot, to represent a blob of solder.

Click on the picture to find out more from the excellent Doctronics website:

Now try Question 4  

For more info, go to http://www.kpsec.freeuk.com/index.htm, an excellent site from Kelsey Park School

Block diagram.

This is a block diagram for a domestic burglar alarm.

With a block diagram we can split a complex system into a number of smaller sub-systems.

Often a complex circuit is built on several boards with each sub-system or module on a separate board. This has several advantages:

  • The circuit boards can be built and tested separately.
  • If the circuit goes wrong, the defective module can be easily removed without having to replace everything else.
  • Modifications can be made more easily.

Here is a simple block diagram of a train sound system that might be used for a model railway.


The wiring diagram shows the power supplies to the components of a circuit.

It shows:

  • The way the wires are connected between the components.
  • The way the wires may be in looms
  • The colour of the wires

There are some points that we can note for all electronic circuits:

  • Most electronic circuits use low voltage dc.
  • Most electronic circuits cannot give out a lot of power.
  • There are ways of interfacing low voltage circuits with high power outputs.
  • Often power supplies are omitted from circuits for clarity, but it is essential that they be put in when we build the circuit. The pin-out diagram shows the power supply as well as all the other connections.