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Electronic Systems

1 Introduction

  • This is a very basic introduction into core electronics for all DT students. We are going to cover all of these and more in our specified specialised topic Systems.
  • Electronic systems can have one or many inputs and outputs and a controller between them.
  • The system read in the input signals and controls the the output signals according to the instructions in the program it has been given.


  • Here is an example of a systems diagram from a very good website, please have a look at the resources.

2 Sensors

Light dependent resistor(LDR)

  • When the light falls on the sensor its resistance changes:
  • in the light the resistance is low so the electrons flow
  • in the dark the resistance is high so not much electricity flows.



  • is a temperature dependent resistor.
  • Its resistance changes with temperature
  • in the warm, the resistance is low
  • in the cold, the resistance is high

3 Control component and devices

  • As well as sensors there other components that can provide input into a circuit.

Single Throw Switch

  • This is an on and off switch for simply controlling the circuit to be on or off.



  • this component changes the resistance of a circuit.
  • It limits the flow of the electrons.
  • This maybe to protect delicate components e.g. LEDs or to help control the flow of electricity around a circuit such as using a pull down resistor.


  • acts like a tiny electronic switch.
  • They have three legs - base, collector and emitter.
  • The are made from a semi-conductor and the base acts as a gate controlling the flow from the emitter to the collector.
  • They are useful in sensing circuits to amplify the small current you get from some sensors.
  • They can be extremely small by etching them into silicon wafers known as silicon chips. A mobile phone may contain 2 billion transistor.


4 Outputs


  • A buzzer is an audio device than can be useful as a warning sound.


Light-emitting diode(LED)

  • This gives out light when electricity is passed through, in a range of colours, that can be powerful to light a whole room.

Light-emitting diode - Wikipedia

5 Definition

Input device

  • Something that can give an input signal to the system.

Output device

  • Something that can responses to an instruction to change from the control system.

Input signal

  • Information give to the system from an input device.

Output signal

  • An instruction the system gives to an output device.


  • A set of instructions the system controller has been given to make the electronic system do what it is supposed to do.
  • A transistor can bypass the need for a program as a simple switching action happens due to the rise in voltage on the base of the transistor above 0.6 Volts.


  • An electrical quantity that is a measure of how the device or wire reduces the electric current flow through it.


  • An individual part of a circuit


  • Individual parts are joined together with a conductive material so electricity can flow through them and perform a task.


  • The amount of potential electrical force available that could make electricity flow.
  • Click on this link to see the effects on Voltage and Current


  • The amount of electricity that is flowing through a circuit.
  • Click on this link to see the effects on Voltage and Current


  • A material that allows electricity to flow under certain conditions. It can behave as an insulator or conductor.
  • To learn more about semi-conductors, click on this link.

Exam Style Questions

  1. What are the 3 main components of an electronic system?
  2. Name 2 possible input devices?
  3. Name 2 possible output devices?


  1. Draw a block diagram for a computer, showing some of its input devices and output devices.
  2. Find out the units of resistance and explain how resistance is marked on a resistor.

Extended information