Note that this is only meant to be a rough guide. Its purpose is to give you a feel for the basic operation of electronic devices and systems. This should help you understand what's going on if you go on to study more detailed, theoretically precise, material. Basic electronics courses sometimes make it appear as if electronic engineers have an obsession with voltmeters, batteries, and oscilloscopes. That's because it's often convenient to talk about these when presenting a course at a university, college, or wherever. In reality, the physics and electronics of practical systems like Hi-Fi's, TV's, computers, etc, are much more interesting. For that reason these pages will try to use these more useful examples whenever possible. ...And by the way, I'll keep referring to all this set of pages as a 'course'. This is partly to save time, partly because this is all based on a course I teach, OK?
Electronic systems are used to process information. Figure 1.1 shows a familiar example, a CD-player and Hi-Fi system. For simplicity, only one channel is shown. A real system will handle stereo information & will have pairs of microphones, amps, and speakers, but apart from that the behaves as shown. For this course we will use the Hi-Fi/CD system as an illustration of various basic electronics ideas. We could have chosen some other example - anything, from the control system for a central heating system to a colour TV would do - but the CD/Hi-Fi is convenient since it uses most of the techniques and devices we'll be looking at.
When considering electronic systems we can talk about the information being carried around by some sort of varying signal voltage or current. This signal can be in various forms. For example, it can be an analog signal where the voltage/current level varies in proportion with the value we wish to carry. The CD system illustrated in figure 1.1 uses both analog and digital signals. The microphone produces an output voltage which changes in proportion with the varying air pressure falling upon it. These variations in voltage have the same pattern as those of the air pressure (i.e. the sound waves). For this reason the pattern of voltage fluctuations is said to be an analog of the sound pattern.
The voltage fluctuations produced by a normal microphone are very small. Hence they have to be enlarged with a suitable amplifier. In the diagram this is called a pre-amplifier. This name is used to indicate an amplifier place at the front of a system whose job is to boost weak signals up to a more useful level. The amplified analog voltage pattern is then passed to a circuit which converts it into a stream of binary digits which are output as a pattern of high and low voltages representing the signal pattern of 1's & 0's. One of the most common choices (TTL or Transistor-Transistor Logic) uses any voltage in the range 3ˇ5 Volts to 5ˇ0 Volts as a '1' and anything from 0ˇ5 Volts to 2ˇ5 Volts as a '0'. Unlike analog signals, the precise digital voltage levels aren't usually important.
This flexibility about the exact voltage required is one of the main advantages of digital systems over analog ones. Slight changes in voltage don't change the actual information content of a digital signal but may ruin an analog pattern. The digital pattern of information is recorded on the CD as a spiral pattern of pits which can be read by the CD player to recover the stream of binary 1's & 0's or bits.These are then converted back into the appropriate analog voltage pattern which is amplified and used to drive loudspeakers. These push and pull the air in the listening room to reproduce the sound wave patterns originally recorded falling on the microphones. During this course we will use various parts of this system as examples to show how electronics is put into use. However, before doing that, we need to sort out some general points about electronic systems and signals.
Content and pages maintained by: Jim Lesurf (firstname.lastname@example.org)
using HTMLEdit2 on a StrongARM powered RISCOS machine.
University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.