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Electronics for dummies - McComb G.

McComb G., Boes E. Electronics for dummies - Wiley publishing, 2005. - 433 p.
ISBN: 0-7645-7660-7
Download (direct link): electronicsfordummies2005.pdf
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Chapter 2: Keeping Humans and Gadgets Safe
Many components that you use in electronic equipment, from simple transistors to complex integrated circuits, are quite sensitive to even low amounts of electrostatic discharge. Transistors and integrated circuits can be particularly sensitive to high voltages, regardless of the amount of current. These components include CMOS transistors, integrated circuits, and most computer microprocessors. Other electronic components also are sensitive to very high levels of electrostatic discharge, but you donít normally encounter these levels in everyday life. (You can read more about CMOS, transistors, and other components in Chapter 4.)
Not all electrical components are static sensitive, but for safetyís sake, develop static-safe work habits for all the components that you handle. Table 2-1 lists the major electronic components and how susceptible they are to damage from static discharge. Read Chapters 4 and 5 for more information on what these components do.
Table 2-1 Static Sensitivity of Common Components
Low Medium High
resistors bipolar transistors CMOS transistors and
integrated circuits
capacitors TTL integrated circuits MOSFETs
diodes many linear integrated microprocessors and
circuits related components
transformers
coils
all passive components,
such as batteries,
switches, and connectors
Tips for reducing static electricity
You can bet that most of the electronic projects you want to build contain at least some components that are susceptible to damage from electrostatic discharge. You can take a number of simple steps to prevent exposing your projects to the dangers of electrostatic discharge:
Use an anti-static mat. An anti-static mat acts to reduce or eliminate the chance of static building up on your table and yourself as you work with an electronic device. You can find anti-static mats in both table-top and floor varieties. The table-top mats look like a sponge, but itís really conductive foam. You can (and should) test the conductivity of the mat by placing the leads of a multimeter (a piece of testing equipment you can
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36
Part I: Getting Started in Electronics
read more about in Chapter 9) on either side of a length of the mat. Dial the meter to ohms. You should get a definite reading and not an infinitely open circuit (a circuit that has a break in it; see Chapter 7 for more about circuits).
Use an anti-static wrist strap. As a further aid in reducing static electricity, also wear an anti-static wrist strap when working on electronic gear. This wrist strap, like the one shown in Figure 2-1, grounds you at all times and prevents static build-up. This strap is one of the most effective means of eliminating electrostatic discharge ó and itís one of the least expensive. Most anti-static wrist straps cost under $5 and are worth every penny. To use the strap, roll up your shirt sleeves and remove watches, bracelets, rings, and any other metallic objects. Wrap the strap around your wrist and make sure that itís tight. Securely attach the wire from the wrist-strap to a proper earth ground, as the instruction sheet that comes with the strap explains.
Wear low-static clothing. Your choice of clothing can affect the amount of static build-up in your body. Whenever possible, wear natural fabrics, such as cotton or wool. Avoid wearing polyester and acetate clothing because these fabrics have a tendency to develop a whole lot of static. A cotton lab overcoat not only looks trendy (in that geeky sort of way), but it can reduce static electricity. Many chemical and industrial supply houses sell lab coats for reasonable prices. You also can find suitable overcoats, smocks, and aprons at many hardware stores.
Figure 2-1:
An antistatic wrist-strap reduces or eliminates the dangers of electrostatic discharge.
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Chapter 2: Keeping Humans and Gadgets Safe
37
Grounding your tools
The tools you use when building electronics projects can also build up static electricity. A lot of it, in fact. If your soldering pencil operates from AC current, ground it as a best defense against electrostatic discharge. Thereís a double benefit here: A grounded soldering pencil not only helps prevent damage from electrostatic discharge but also lessens the chance of a bad shock if you accidentally touch a live wire with the pencil.
Cheapo soldering pencils use only two-prong plugs and donít have a ground connection. You canít find a really safe and sure means of attaching a grounding wire to the soldering pencil, so the best bet is to just buy a new and better pencil. You can purchase a grounded soldering pencil for less than $30, including an assortment of tips.
As long as you ground yourself by using an anti-static wrist strap, you generally donít need to ground your other metal tools, such as a wire wrapping tool, screwdrivers, and wire cutters. Any static generated by using these tools is dissipated through your body and into the anti-static wrist strap.
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