There will generally be three of these bands together starting at one end of the resistor, a gap, and then a single band at the other end of the resistor. The single band indicates the accuracy of the resistor value. While gold and silver represent the fractions 1/10 and 1/100, they’re also used to indicate how accurate the resistor is; gold is ±5 percent and silver is ±10 percent.
Figure A-1 shows the arrangement of the colored bands. The resistor value uses just the three bands. The first band is the first digit, the second the second digit, and the third “multiplier” band is how many zeros to put after the first two digits.
Figure A-1: Resistor color codes
Let’s say the digit-1 band is red, the digit-2 band is violet, and the multiplier band is brown. That makes this a 270 Ω resistor, or 27×101. Similarly, a 10 kΩ resistor will have bands of brown, black, orange (1, 0, 1,000).
B
BASIC SKILLS
If you’re going to be a postapocalyptic maker and survive the land of the walking dead, then you’ll need a few key electronics skills. This appendix is a quick guide to the basics, such as joining wires together, soldering, and using a multimeter. Flip here anytime you need a refresher. It may save your life!
STRIPPING WIRES
For an apocalypse survivor, stripping the insulation off wires is a skill that belongs near the top of the list. The devices in this book will help you stay alive, and to build them, you’ll often need to join insulated wires together or fit them into a screw terminal. The first step in that process is exposing the bare wire.
To strip a wire, use a blunt pair of pliers to grip the wire and pull off the insulation with a sharp pair of wire cutters (also called snips). Figure B-1 shows the process.
Figure B-1: Stripping wires
Grip the wire with pliers (Figure B-1a). If your wire is long, you could wrap it around your fingers instead. Either way, the idea is to stop the wire from moving. Next, gently pinch the wire with the cutters at the position where you want to remove the insulation. Apply just enough pressure to almost cut through the insulation without cutting into the wire inside, then pull the insulation away (Figure B-1b). If the snips start to slip as you pull, just squeeze them a bit tighter.
Mastering this skill can take a while, so practice on some old wire before you try it on something important. If you cut the last good wire in your cache too short, you could find yourself unable to complete your latest antizombie invention until the next supply run—when it might be too late.
JOINING WIRES BY TWISTING
Knowing how to twist wires together is a useful skill, too, especially if you haven’t come across any solder in your scavenging trips. If done properly (as illustrated in Figure B-2), just twisting the wires together can make pretty good electrical connections.
Figure B-2: Joining wires by twisting
First, strip about half an inch (15 mm) of insulation off each wire (see “Stripping Wires” on page 227). Then, if your wire is stranded rather than solid, use your thumb and forefinger to twist each wire on its own and keep all the strands together (Figure B-2a). Next, place the two wires side by side, lining up the ends of the insulation, and twist the wires around each other (Figure B-2b). Try to make sure that the wires actually go around each other, rather than leaving one wire straight while the other wraps around it. This can be difficult if the wires are of different thicknesses.
Finally, coil the intertwined wires into a tight ball (Figure B-2c) and wrap the whole thing in electrical tape or heatshrink tubing (see “Using Heatshrink” on page 235). You can also use pliers to really tighten up the joint.
If you have soldering equipment, then you can make the connection mechanically stronger and more electrically reliable by heating the little knot with a soldering iron and feeding solder into it, as I describe in the next section.
If you want to know how NASA does it, take a look at this link: http://makezine.com/2012/02/28/how-to-splice-wire-to-nasa-standards/.
SOLDERING BASICS
Soldering is much easier than it looks, and you don’t need to spend a lot of money on a fancy soldering station. During an apocalypse, your options will be limited, but a basic starter kit (see Figure B-3) will work just fine.
You can find basic soldering kits at an auto parts store or even at some hardware stores. If you are buying in advance of the apocalypse, then Adafruit sells a great starter kit (product 136) that also includes a multimeter, hookup wire, and various other useful bits and bobs.
Figure B-3: A basic soldering kit
There are lots of accessories and tools that can make soldering quicker, but these are by no means essential. Here’s all you really need:
A soldering iron Look for an iron with a power rating of 30W or more, with a fine tip (say 1/25 inch, or 1 mm). Before the zombie apocalypse, just buy one that’s AC powered. To prepare, you could also buy a soldering iron that runs on 12V DC and keep it with your emergency supplies; that way, you’ll have an iron you can power from a car battery. These soldering irons, intended for working on the electrical components of cars, are quite common.
Solder If you buy a soldering kit, it will probably come with a coil of solder. Solder comes in two flavors: leaded and lead-free. Leaded solder melts at a lower temperature and is generally easier to use than lead-free solder. But please don’t eat either, no matter how desperate your food situation becomes.
Snips You’ll need a good pair of wire cutters to cut wires close to the surface of a PCB and for stripping wire.
A damp sponge or cloth Any old sponge will do. You’ll use it to wipe the tip of the iron when there’s excess solder.
WARNING
Soldering irons get hot. In fact, they get really hot, much hotter than the maximum temperature of your kitchen oven. So it goes without saying that if you touch the hot end of a soldering iron, you’ll get a serious burn. This is not an activity for unsupervised children. Similarly, lead is a toxic element that is not at all good for you, so you may prefer to use lead-free solder, despite it being a little harder to work with.
JOINING WIRES WITH SOLDER
To join together two wires with solder, start by following the instructions in “Joining Wires by Twisting” on page 229. Then, you can solder the joint. The trick with soldering is to always make the solder flow into the thing you’re soldering; Figure B-4 shows solder flowing into the ball of wires from Figure B-2c.
Many beginners make the mistake of creating a blob of solder on the tip of the iron and then blobbing it onto the wire. This usually results in poor quality dry joints that may look okay but will fail quickly and, before they fall apart, may not make good contact with the wire. Therefore, you’ll want to heat the wire you want to solder before you touch the solder to it.
Figure B-4: Running solder into the joined wires
With that in mind, you can join your twisted wires as follows:
1. Turn your iron on and leave it to heat up. If your kit didn’t come with a stand for the soldering iron, make sure that you prop it somewhere safe so that the hot end is not touching anything.
2. Touch the end of the solder to the tip of the iron to see if it is hot. If it immediately melts and flows over the tip of the iron, then the iron is ready.