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