Components

Electronic components can be divided into two groups:

1. Discrete electronic components These are separate components that you can combine together to make a circuit on a breadboard, printed circuit board or veroboard (discrete means separate). Examples are resistors [resistors: components which resists or 'slows down' the current in a circuit by acting against the flow of electrons. Resistance is measured in ohms. ], transistors [transistors: components which do not conduct electricity, unless they are turned on by a (different) electrical current. This means they can be used as switches, amplifiers and in other ways. ], capacitors [capacitors: circuit components which store and discharge electrical current. It is made from two parallel metal plates separated by an insulator (called a dielectric). ], relays [relays: type of switch which which uses an electromagnetic coil to connect two or more contacts, which close when the coil is energised. Use of relays enables a very small voltage in the relay circuit to control a much larger one in a separate circuit. ] and light emitting diodes or [LEDs: stands for Light-Emitting Diodes. LEDs glow when current passes through them. ].

Discreet components

These components are called discrete because you can select them individually and combine them to make up the circuit you require. Discrete components can also be used as external components of an integrated circuit system. For example a 555 astable [astable: (a circuit) having two states, neither of which is stable. An astable circuit therefore oscillates between the two states, giving a constant on/off digital output. Used, for example, to make LEDs flash continuously. ] integrated circuit requires two discrete resistors and a discrete capacitor to make it work.

Integrated circuits (ICs)

These are miniature circuits etched on to a piece of silicon or chip. These chips are encapsulated inside a protective plastic package, and nowadays are manufactured in vast numbers. The circuits inside the package are arranged in different configurations for particular purposes, but the most common type of configuration is called the dual-in-line or DIL package, which has two rows of connecting 'legs', one on each side.

A Surface Mount package integrated circuit - far smaller than a finger-tip

You don't need to understand how the circuit inside a silicon chip works - there's some quite complicated physics involved. It's best to think of ICs simply as input-output process blocks, as shown below:

Input-output process block

When using ICs you need to know which pins need to be connected, the function of each pin and how the IC is connected to the power supply. A circuit diagram that includes one or more ICs should show the pin numbers and how the pins are connected to the rest of the circuit.