Materials

Modern electronic systems are controlled by microprocessors and microcontrolers - computer-like components which are programmable [programmable: able to take instructions in the form of a sequence of commands ] and can therefore be used in different ways in different products.

Electronic components work together in circuits, and these can be represented in circuit diagrams using standard symbols for the components. You need to know some common inputinput: the term denoting either an entrance or changes which are inserted into a system and which activate/modify a process and outputoutput: the term denoting either an exit or changes which exit a system and which activate/modify a process components, and be familiar with two common types of integrated circuit - the 555 timer and Op-Amp circuit.

There are three types of materials used in electronic components:

An electrical insulator

1. Electrical conductors are materials that allow electricity to flow through them easily.
2. Electrical insulators are materials that prevent electrical flow. In the diagram to the right, the insulating material (plastic) surrounds the conducting material (copper wires).
3. Semi-conducting materials exhibit both conducting and insulating properties. The way in which the material is connected to a power supply determines whether it will conduct an electrical current or prevent it from flowing.

The most common semi-conducting material is silicon. Silicon needs to have very small amounts of other elements such as boron and phosphorous added to it in order to become a semi-conductor. This is called doping. Doped silicon is used to make components such as:

• Transistors
• Diodes
• Integrated circuits

A diode

The simplest kind of semiconductor device is a diode. In a diode the electrical current can be made to flow in one direction only (see diagram below). If the diode is reversed the flow of current is stopped. This behaviour is due to the semi-conducting property of the doped silicon.

Another semi-conducting material is germanium, but this material is used less widely than silicon.

The ease with which electricity flows through a material is called its resistivity. The value of resistivity is measured in ohms. The higher a material's resistivity, the more difficult it will be for electricity to flow through it:

• Insulators have very high resistivity values.
• Conductors have low resistivity values.