Digital and Analogue Signals

What is a signal?

When you hear someone talking you usually understand what they are trying to say. The sound waves carry information. They are a form of signal.	A microphone changes sound waves into an electrical signal. This is a changing (alternating) voltage.	A radio transmitter transmits radio waves which carry a signal.	Light or infra red signals can travel down optical fibres. This is how the internet comes into most of our homes.

An oscilloscope is a device which allows us to "look at" electrical signals by producing a trace.

Here is a trace produced by an analogue signal and a digital signal.

Notice that the analogue signal varies with time. The height (amplitude) and frequency can be any value. The digital signal, however, can only be one of two values, generally on and off.

You may have noticed that just about all forms of communication these days are going digital (television, mp3, radio etc).

There are a number of reasons for this including:

Digital signals are much less prone to interference
Signals can become distorted by picking up "noise", e.g. when your radio crackles when someone is using something electrical nearby. It is much easier to filter out noise from a digital signal because it is much easier to recognise it. For this reason digital music, television etc is superb quality.

Digital signals can be processed easily by computers
Computers think in 0's and 1's. Information is dealt with as lots of 0's and 1's. This is basically what a digital signal is, lots of 0's and 1's.