Electronics All-in-One For Dummies. Doug Lowe
time you finish Book 2, Chapter 6, you’ll know what the designation 2N3904 NPN means.
Integrated circuits
An integrated circuit is a special component that contains an entire electronic circuit, complete with transistors, diodes, and other elements, all photographically etched onto a tiny piece of silicon. Integrated circuits are the building blocks of modern electronic devices such as computers and cellphones.
You learn how to work with some basic integrated circuits in Book 3. To get started, you’ll want to pick up a few each of at least two different types of integrated circuits: a 555 timer and an LM741 op-amp. These chips are shown in Figure 3-20.
FIGURE 3-20: Two popular integrated circuits: A 555 timer and an LM741 op-amp.
One Last Thing
There is, of course, one last thing your mad-scientist lab will need to make it complete. That one last thing is a sign that properly warns your friends and family that you are indeed a mad scientist. You have my express permission to photocopy the sign, shown in Figure 3-21, and place it in a prominent spot near your workbench.
FIGURE 3-21: Make sure your friends and family are properly warned.
Chapter 4
Staying Safe
IN THIS CHAPTER
When I was a kid, I helped a good friend named Barry who built a Tesla coil. By “helped,” I mean that I hung out in his garage and watched while he meticulously wrapped thousands of turns of bare copper wire around a huge glass milk bottle, painted it with dozens of coats of lacquer, and polished the brass ball that attached to the very top of the coil. I’m quite certain he couldn’t have done it without me.
When it was done, we plugged it in and marveled at what it could do. Sparks flew at random a foot or two into the air from the ball at the top of the coil. If you held a crowbar in one hand, you could draw a spark several feet from the ball to the crowbar. The current coming off the ball flew through the air and into the crowbar, and then passed through our bodies and into the ground. You could also light up a fluorescent light tube simply by holding the tube in your hand within a few feet of the coil.
To this day, I cannot believe Barry’s parents let him build it. I know my parents wouldn’t have let me build one. My mom was kind of like the mom in A Christmas Story, who wouldn’t let her son Ralphie have a Red Ryder BB gun (the one with a compass in the stock and this thing that tells time) because “you’ll shoot your eye out.”
That was my mom. No Tesla coils for me. Too dangerous.
None of the electronic projects described in this book are anywhere near as dangerous as a Tesla coil. In fact, most of them pose no threat at all. That being said, it’s important to remember that whenever you’re working with electricity, you’re working with something that’s potentially very dangerous.
The possibility of electric shock is always present whenever you work with electricity, but there are other potential dangers as well. You probably won’t shoot your eye out, but if you’re not careful, you might start a fire or otherwise injure yourself or someone else.
The purpose of this chapter, then, is to keep you safe while you experiment with electronics. Please read it well, and please heed every bit of advice I give here.
Facing the Realities of Electrical Dangers
There’s no escaping the simple fact that an electric shock, if strong enough, can kill you. So whenever you work with electricity, you must be sure to take every precaution you can to avoid being the recipient of a shock strong enough to do damage.
In the United States, somewhere between 500 and 1,000 people die every year from accidental electrocutions. Many of those are industrial or weather-related accidents in which people come into contact with downed power lines. But many of them are completely avoidable accidents that happen in the home. In the sections that follow, I give you specific guidelines for avoiding accidental electrocution.
Household electrical current can kill you!
Too many people are under the false impression that the 120 volts of alternating current running through household electrical wires isn’t enough to kill. So let’s start by getting one fact straight:
You’re exposed to household electrical current primarily in two places: in electrical outlets and in the lamp sockets within light fixtures. As a result, you should be extra careful whenever you plug or unplug something into or from an electrical outlet, and you should be careful whenever you change a light bulb. Specifically, you should follow these precautions:
Never change a light bulb when the light is turned on. If the light is controlled by a switch, turn the switch off. If the light isn’t controlled by a switch, unplug the light from the wall outlet.
If an extension cord becomes frayed or damaged in any way, discard it. When the insulation begins to rub off of an extension cord, the shock hazard is very real.
Never perform electrical wiring work while the circuit is energized. If you insist on changing your own light switches or electrical outlets, always turn off the power to the circuit by turning off the circuit breaker that controls the circuit before you begin. Many people die every year because they think that they can be careful enough to safely work with live power.IS IT TRUE THAT CURRENT, NOT VOLTAGE, KILLS?There is an old adage that “it’s the current that kills, not the voltage.” Although this statement may be technically true, it’s also dangerously misleading. In fact, it stems from a fundamental misunderstanding of what current and voltage are. It can cause you to take dangerous risks if you don’t understand the relationship between current and voltage.The danger from electric shock occurs as current passes through vital parts of your body — specifically, your heart. It takes only a few milliamperes of current to stop your heart. At somewhere around 10 mA, muscles seize up, making it impossible to let go if you’re holding a live wire. At around 15 mA, the muscles in your chest can seize up, making it impossible to breath. And at around 60 mA, your heart can stop. It takes only a few moments of exposure for these effects to occur.So yes, it is current passing through your body that can kill you.But current is inseparable from voltage. Current can’t happen without voltage, and all other things being equal, the greater the voltage, the greater the current. As a result, it’s very difficult to receive a lethal shock