Читать книгу Electronics For Kids For Dummies - Shamieh Cathleen - Страница 5

One of the many fun things you can do with electronics is control lights. You can turn lights on and off, have them turn on only when the room gets dark, make them blink, change their timing, and much more.

For your first circuit-building project, you make your own flashlight using a special kind of electronic light bulb known as an LED (which is short for light-emitting diode).

So let’s getting started making an LED flashlight!

Gather the Parts for the LED Flashlight

The main ingredients of your LED flashlight are a battery, an LED, and a resistor. They are the components of your circuit. Each component is like a piece of a puzzle: It has a certain job to do and it works with the other components to form the completed circuit.

Using electrical tape and craft foam, you can transform your three-component circuit into a portable, brightly colored device that you can show off – maybe even sell – to your friends.

Check out Project 1 for where to buy parts, tools, and other supplies. Grab a pair of scissors and your needle-nose pliers, then gather the items in the following list (shown in Figure 2-1):

✓ One 9-volt battery

✓ One ultrabright clear 5 millimeter LED

✓ One 470 Ω resistor (look for a stripe pattern of yellow, violet, brown, and then any color stripe)

✓ A roll of 3/4-inch wide electrical tape (you need roughly 4 inches in length from this roll)

✓ One 9-by-12-inch sheet of adhesive-backed craft foam (any color)

Figure 2-1

Before you start building your flashlight, you should know a few things about the three main circuit components (the battery, LED, and resistor).

Energize Your Flashlight

Chances are you’re familiar with 9-volt batteries like the one in Figure 2-1. The battery’s job is to provide the electrical energy needed to power the LED in your flashlight circuit.

Explore your battery

Every battery has two terminals, which are the metal pieces that stick out from the top of a 9-volt battery (see Figure 2-2) or the metal ends of an AA, AAA, C, or D battery. One terminal is positive and is labeled with a +. The other terminal is negative and isn’t labeled. Locate the positive and negative terminals on your 9-volt battery. Note that the two terminals look different.

Figure 2-2

When you connect your battery in a circuit, you connect the positive terminal to one part of the circuit and the negative terminal to another part of the circuit. The battery voltage is a form of energy (specifically, potential energy) that exists between the two terminals. Voltage is measured in volts, which is abbreviated V.

Voltage and current

When you connect a battery in a circuit, the battery’s voltage forces electrons to flow out of the battery, through the circuit, and then back into the battery. But what are electrons, you ask?

Electrons are tiny particles that have a special quality known as negative charge. Electrons exist inside atoms, which are the building blocks of matter. When a bunch of electrons break loose from their atoms and travel together in the same direction, that flow of electrons is called electric current, or simply current.

In your LED flashlight circuit, electric current gives your LED the energy it needs to light up. And the 9-volt battery provides the energy (voltage) needed to push the current through the circuit.

Batteries are one type of voltage source, providing voltage to force current to flow through circuit components.

Technically, what we call a battery is really a cell. A battery is really two or more cells connected together electrically. It’s good for you to know that, but I still use the term battery to refer to a cell (as do most people).

Get to Know Your LED

You may be familiar with LEDs if you have an LED flashlight or use LED bulbs in your home. An LED, or light-emitting diode, is a device made of a special material known as a semiconductor. A diode is the simplest type of semiconductor device (meaning, component).

Diodes, LEDs, and other semiconductor devices have unique properties that make them useful. For instance, they don’t always allow current to pass through them. Instead, they’re picky about what’s going on in the circuit and will allow current to flow only under certain conditions.

Diodes and bicycle tires

Have you ever pumped air into a bicycle tire? The tire contains a valve that allows air to flow into the tire, but not out of the tire. You have to apply enough pressure to the pump to force air through the valve.

A diode acts like a valve for electric current. Current flows only one way through a diode (like cars on a one-way street – we hope), and only when you apply a high enough voltage (like pressure) to the diode.

Seeing light from LEDs

A light-emitting diode is a type of diode that emits, or gives off, visible light. The light emitted from an LED can be red, orange, yellow, green, blue, violet, pink, or white, as shown in Figure 2-3. The color depends on the materials and processes used to make the LED.

Figure 2-3

LEDs also come in several shapes and sizes. The LEDs you use in the projects in this book have round, domed cases that are either 5 mm (millimeters) or 3 mm high.

There are two types of LEDs:

✓ Diffused LEDs have colored plastic cases (like tinted windows) to diffuse, or spread out, the light so it’s easier to see. The color of the plastic case is usually the same as the color of the light.

✓ Clear LEDs have clear plastic cases but still emit colored light.

All the LEDs in Figure 2-3 are clear 5 mm LEDs. Figure 2-4 shows an assortment of LEDs, including a 5 mm clear LED that gives off an orange light. (It’s the unlit version of the LED that is second from the left in Figure 2-3.)

Figure 2-4

You can’t tell what color a clear LED emits just by looking at it if it’s not connected in a circuit. If you buy any clear LEDs, be sure to store them in a container or bag labeled with the color they emit.

Examine your LED

Take a good look at your LED and compare it to the LEDs shown in Figure 2-5. The actual semiconductor diode is tiny and is on a piece of metal inside the plastic case. The two stiff wires attached to the plastic case are leads that enable you to connect the tiny diode to a circuit.

Figure 2-5

Because LEDs conduct current in only one direction, you need to know which way to connect the LED in your circuit. One side of the LED is the negative side (known as the cathode) and the other side of the LED is the positive side (known as the anode). Electric current flows from the anode to the cathode of an LED but not the other way around. You can tell which side of an LED is which in three ways:

✓ Compare the lengths of the leads. The shorter lead is the cathode (negative side) and the longer lead is the anode (positive side). (See Figure 2-5, left.)

✓ Peek inside the plastic case. The lead attached to the larger piece of metal inside the case is the cathode (negative side); the lead attached to the smaller piece of metal is the anode (positive side). (See Figure 2-5, left.)

✓ Look (or feel) for a flat edge on the plastic case. This flat edge is on the cathode (negative side) of the LED. (See Figure 2-5, right.)

Look at the leads of your LED. Can you tell which one is the shorter lead? Now look inside the case of your LED. (You may need to shine a flashlight on the case to see inside better.) Can you spot the larger and smaller pieces of metal? Finally, run your finger around the bottom edge of the plastic case. Can you feel a flat edge?

Being able to distinguish the anode from the cathode by peeking inside the case or finding the flat edge may come in handy when you do other projects in this book, because you may want to cut, or clip, the leads of an LED to create a neater circuit. After you clip the leads, you can’t figure out which side is which by comparing the lengths of the leads.

Orienting an LED in a circuit

When you connect an LED in a circuit, you need to orient it so that current flowing from the positive terminal of the battery flows into the positive side (anode) of the LED. If you put the LED in backward, current will not flow. (I tell you which way to orient the LEDs you use in projects in this book.)

To conduct current and emit light, most LEDs require between 2.0 and 3.4 volts to be applied across the leads. The exact voltage needed depends on the color of the LED. A 9-volt battery is powerful enough to push current through any LED, but a 1.5-volt battery, such as an AA or AAA battery, isn’t strong enough. For this reason, you use a 9-volt battery rather than an AA or AAA battery for your LED circuit.

Never, ever connect a 9-volt battery directly to an LED. If you do, you may damage the LED. LEDs can handle only a certain amount of current before they have a meltdown, and a direct connection with a 9-volt battery pushes way too much current through the LED. Chances are, the LED will light briefly and then go out for good, but the LED may also melt, make a mess, and smell up your house.

Protect Your LED with a Resistor

To limit the current that flows from your 9-volt battery through your LED, you insert a resistor in your circuit. Resistors slow down current, like a kink in a hose slows the flow of water.

Figure 2-6 shows you a variety of resistors. Every resistor has two leads, and it doesn’t matter which way you insert a resistor into a circuit. Current flows either way through a resistor. (Resistors are not semiconductors, so they are not picky.)

Figure 2-6

Resistors don’t require a minimum voltage like LEDs do (not picky!). Current flows through a resistor even with a tiny voltage applied. The higher the voltage you apply to a resistor, the higher the current that flows through the resistor – up to a point. Too much current can melt a resistor. (Don’t worry. You won’t melt any resistors for the projects in this book – as long as you follow the instructions!)

Understanding resistance

Every resistor has a value known as its resistance (what a surprise). The higher the resistance, the more the resistor restricts current. Resistance is measured in ohms (pronounced “omes”), and the symbol for ohms is Ω (which looks like an upside-down horseshoe and is the Greek letter omega).

Some resistances are measured in kilohms (pronounced “kill omes”), which means thousands of ohms. The symbol for kilohms is kΩ. Other resistances are so large they are measured in megohms (pronounced “meg omes”), which means millions of ohms. The symbol for megohms is MΩ. (You may be familiar with the prefixes, kilo, which means thousands, and mega, which means millions, from your math classes. And you’ve probably heard of measurements such as kilometer, as in the k in a 5k race, and megabyte, as in “My laptop has 4 megabytes of RAM.”)

For your LED flashlight, you need a resistor with a value of 470 Ω. But resistors don’t have their values stamped on their cases, so you need to know how to identify a 470 Ω resistor. You can tell what the resistance of a specific resistor is by looking at the colored bands on its case. Think of the colored bands as a code. The color and position of the bands tell you the value of the resistance.