Introductory Electronics Tutorial  -  System Synthesis


Learning Objectives


Systems Approach

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:



Here is a typical circuit that you might come across in the school physics or electronics lab:




Now try out these interactive questions:


Question 1

Can you identify the systems in your computer?


Question 2

Fill in the spaces about systems.


Question 3

Identify the systems in a burglar alarm.



A Circuit diagram tells us:

This circuit diagram is for a simple burglar alarm.  Don't worry at this stage what the components are.



This circuit diagram shows a 4-bit counter, using integrated circuit chips.  You don't need to know what goes on inside, but you do need to know how to make the connections between the different pins.  When you use a chip like this, you will get a pin-out diagram, which tells you which pin does what.  You can see the little numbers, which refer to the pins.


Diagram by Gargan, Wikimedia Commons


And this picture shows a pin out diagram for a 555-timer.



Question 4

This interactive question gets you to think about circuit diagrams




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.


Wiring Diagram

The wiring diagram is different to a circuit diagram.  It shows the connections between major components of circuit.  The picture shows the wiring diagram of a vehicle immobiliser.


Diagram by Leonard G, Wikimedia Commons

It shows:

  • The way the wires are connected between the components;

  • The way the wires may be in looms;

  • The colour of the wires;

  • The pins on the components to which the wires are attached.

As you can see from the diagram, there is no information whatever about the circuit within each of the boxes.


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 are put in when we build the circuit. The pin-out diagram shows the power supply as well as all the other connections.


  • Electronic systems consist of input, process, and output;

  • There may be feedback;

  • Circuit diagrams show the layout and connections of components;

  • Engineers use circuit diagrams to assemble the circuit.

  • Block diagrams show how a complex circuit can be broken down to subsystems.

  • Subsystems may be on separate boards that can be exchanged;

  • Wiring diagrams show how the circuit systems can be wired together.


Some excellent pages from Kelsey Park School


Doctronics - Circuits


How Amplifiers Work


How burglar-alarms work




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