Real world Applications of Electronics
This chapter introduces some of the real world applications of Electronics; 1. Audio Systems 2. Radio Transmission & Reception 3. Control Systems 1. AUDIO SYSTEMS: Any system operating at audio frequencies (20 to 20,000 Hz) is called an Audio System, e.g. an intercom, music systems etc. Following diagram (fig.1.1) shows the main features of such an audio system;
FIGURE 1.1: Main blocks of an audio system 1.1 Radio tuner: It receives radio signals and converts them into electrical signals.
FIGURE 1.2 1.2 CD player: It converts music and sound recorded digitally on a compact disc (CD) into analogue electrical signals. A CD consists of two plastic layers with a silvered coating sandwiched between them (above fig. 1.2). As shown in fig. 1.2, a series of dimples having spaces between them is used to record the music and sound data. Digital logic ‘1’ represented by a dimple and a space represents logic ‘0’. A beam of light from a low-power laser is focused on the spinning disc from below. The beam is reflected back in case there is no dimple, and gets detected by a photodiode. Where there is a dimple, the beam is scattered sideways and is not detected. This provides a stream of bits, either ‘0’ or ‘1’. Complex logic circuits process these 1s and 0s, eventually producing two analogue signals for the left and right stereo channels. 1.3 Tape deck: Relatively newer audio systems do not have a tape deck, but there are still plenty of older systems which use magnetic tapes for recording music & sound data. The plastic tape is coated with a layer containing a magnetic substance such as chromium dioxide. This becomes organized into microscopic regions known as domains. Each domain is equivalent to a very small magnet. In an unrecorded tape, the domains are arranged irregularly, so there is no overall magnetization.
To record sound on a tape deck the tape passes through a gap in a magnetic recording head. A signal from an amplifier causes an alternating magnetic field in the gap, which causes the domains to change direction.
FIGURE 1.4 In some regions they are mainly pointing one way (→ below). In other regions they are mainly pointing the other way (←). The directions and the proportions of domains affected correspond to the waveform that is being recorded. The diagram below shows the original analogue audio signal and the corresponding arrangement of the domains.
FIGURE 1.5 When the tape is played back, it passes under the playback head. There the magnetic fields produced by the domains on the tape induce alternating currents in the coil. These currents are a reproduction of the original signal current. 1.4 MP3 Player: An MP3 player can be used as a source of recorded music. The term MP3 refers to a technique for compressing digital music files so that they become small enough to be stored in a reasonably small memory chip. MP3 files may be downloaded from sites on the World Wide Web. The development of cheap ‘flash’ memory chips has made MP3 players affordable. This has made MP3 and more recent systems very popular.
1.5 Digital versatile discs (DVDs) are another possible audio source, although they are more frequently used for recording films with multiple sound tracks. They may include special multimedia features, such as subtitles in several languages. DVDs can be used for audio recordings of high quality. They are very similar to compact discs but have smaller dimples, which are more densely packed, and so store a much larger amount of data (up to 17 Gb compared with 700 Mb on a compact disc). 2. RADIO TRANSMISSION & RECEPTION: 2.1 Radio Transmission: If we apply the output from an oscillator to a pair of metal rods, electrons rush to and fro along the rods. Their rapid motion generates an electromagnetic field. Electromagnetic waves spread outward from the rods, like ripples on a pond, only in three dimensions. If the frequency of the oscillator is between...
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