Electronics All-in-One For Dummies. Doug Lowe
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Название: Electronics All-in-One For Dummies

Автор: Doug Lowe

Издательство: John Wiley & Sons Limited

Жанр: Отраслевые издания

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isbn: 9781119822134

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СКАЧАТЬ and staple or clamp the wire to the workbench, leaving the stripped end free so you can attach the alligator clip from your antistatic wristband to it. (Note that this technique works only if the building uses metal pipes throughout. If the building uses plastic pipe, the water-pipe won’t provide a proper ground.)

      Warning An often-recommended way to connect the wristband to an earth ground is to connect it to the ground receptacle of a properly grounded electrical outlet. I’m definitely not a fan of this method, as the key to its operation lies in the term “properly grounded electrical outlet.” All it takes is one stupid wiring mistake, or one wire shaken loose by a sonic boom or a mild earthquake, and suddenly that ground wire might not be a ground wire anymore — it might be energized. Call me paranoid if you wish, but there’s no way I can recommend strapping a conductor around your wrist and then plugging it into an electrical outlet.

      Reading Schematic Diagrams

      IN THIS CHAPTER

      Bullet Examining how schematic diagrams provide a road map for electronic circuits

      Bullet Looking at the most commonly used component symbols

      Bullet Noting how voltage supply and common ground circuits are often drawn

      Bullet Seeing how components are typically labeled

      I love maps. I think I’ve kept every map I’ve used on every trip I’ve taken. I have big maps of entire countries and states, maps of cities, walking maps, maps of parks and museums, and even subway maps. My favorite maps are topographical maps of the areas where I’ve gone on weeklong backpacking trips. These maps show not only the routes I’ve hiked, but also elevation lines that represent every painful uphill step I’ve carried my 50-pound backpack up.

      Without maps, we’d be lost. We’d never get to our destinations because we wouldn’t know where the roads are. Think of all the sights we’d miss along the way!

      Electronics has its own form of maps. They’re called schematic diagrams. They show how all the different parts that make up an electronic circuit are connected.

      In this chapter, you learn about the symbols used in schematic diagrams and the conventions used to draw them.

      I’ve read a lot of computer programming books in my day, and I’ve written a few too. In a computer programming book, the first complete computer program usually shown is a program called Hello World, a program that simply displays the text “Hello World!” on a screen, and then quits. It’s pretty much the simplest possible computer program that can be written. It doesn’t do anything useful, but it’s a great starting point for learning how to write computer programs.

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      FIGURE 5-1: A simple schematic of a circuit that lights a lamp.

      This diagram contains two symbols representing the two components in the circuit: a 1.5 V battery and an incandescent lamp. The lines that connect the two components represent conductors, which could be actual wires or traces of copper in a printed circuit board.

      Schematic diagrams always depict conventional current flow, which, as you learn in Chapter 2 of this minibook, means that current flows from positive to negative. Thus, the current flows from the positive terminal of the battery through the lamp and then back to the negative terminal of the battery.

      Remember In reality, conventional current flow is the opposite of the actual flow of electrons through the circuit. The negative side of the battery has an excess of negatively charged particles (extra electrons) whereas the positive side has an excess of positively charged particles (missing electrons). Thus, the electric charge flows through the conductor from the negative side of the battery, through the lamp, and back to the positive side. (For more about the difference between real current flow and conventional current flow, see Chapter 2 of this minibook.)

      As it passes through the lamp, the resistance of the lamp’s filament causes the current to heat the filament, which in turn causes the filament to emit visible light.

      Remember One of the most important things to realize about a schematic diagram is that the arrangement of components in the diagram doesn’t necessarily correspond to the physical arrangement of parts in the circuit when you actually build the circuit.

      For example, the circuit shown in Figure 5-1 shows the battery on the left side of the circuit and the lamp on the right. It also shows the battery oriented so that the positive terminal is at the top and the negative terminal is at the bottom. However, that doesn’t mean the circuit would actually have to be built that way. If you want, you could put the lamp on the left and the battery on the right, or you could put the battery at the top and the lamp on the bottom.

      The physical arrangement of the circuit doesn’t matter as long as the component connections remain the same as shown in the schematic. Thus, in this example, no matter how you physically arrange the components, you must connect the positive terminal of the battery to one lead of the lamp and the negative terminal to the other lead.