3. If the tip of the iron is not shiny and bright after this, then wipe it on a wet sponge. This makes a great sizzling noise! Repeat the previous step to tin the tip of the iron with solder. Tinning just means coating a wire or the tip of your iron with solder by heating it up and then pushing the solder onto it.
4. Press the tip of the soldering iron against the little knot of wires and leave it there for perhaps three or four seconds. Then, with the soldering iron still pressed to the knot, push the end of the solder onto the knot. The solder should flow into the knot. If your solder isn’t flowing well, it sometimes helps to feed a bit more solder to the joint, as solder contains cores of rosin flux, which helps the solder to liquefy.
5. Keep feeding the solder in until the whole knot of wires is coated in solder.
6. Remove the tip of your solder thread from the joint and replace the iron on its stand. Make sure that the wires don’t move while you give them 10 or 20 seconds to cool down.
You can also insulate your soldered connection with electrical tape or with heatshrink, as described in “Using Heatshrink” on page 235. If you plan to do this, then you can make a neater joint by soldering the wires side to side, without twisting them together (Figure B-5a–e).
After stripping the ends of the wires (Figure B-5a), tin them with solder (Figure B-5b). If the wire is stranded, the solder should flow between the strands that make up the wire.
Figure B-5: Soldering wires together without twisting them first
Now, lay the wires next to each other (Figure B-5c), heat the wires, and run solder into the valley they make (Figure B-5d). The end result should be a nice, even joined pair of wires (Figure B-5e).
SOLDERING A PCB
Wires are easier to scavenge than complete circuits, but being able to solder to a printed circuit board (PCB) will certainly serve you well during an apocalypse. For example, quite a few of the projects in this book use a screwshield that requires a bit of soldering to put together. Fortunately, the screwshield is a PCB with lots of convenient metal pads that are made for soldering. If you successfully followed the steps described in “Joining Wires with Solder” on page 231, then you shouldn’t have any problems soldering a PCB.
When attaching components to a PCB, the basic idea is that you push a component’s legs through from the top, flip the PCB over, solder the leads to their solder pads, and snip off the excess wire. Figure B-6 shows a component lead being soldered onto a screwshield.
Figure B-6: Soldering a component leg to a PCB
As with all soldering, the trick is to apply the solder to the thing being heated up rather than to the soldering iron, so heat the component leg and touch solder to it. You’ll often get the best results by giving the soldering iron a second or two to heat the component lead and solder pad before you apply the solder to the junction of the soldering iron tip and the component lead. Figure B-7 shows examples of two solder joints, one bad and one good.
The solder joint on the left is best described as “blobby,” and it’s a result of allowing a glob of solder to form on the tip of the iron and then “blobbing” it onto the PCB. The solder joint on the right is close to perfect. See how the whole pad is covered in solder, flowing all the way around the component lead and forming a very gentle little hill of a meniscus.
Figure B-7: Bad (left) and good (right) solder joints
USING HEATSHRINK
When you’re confident in your wire-connecting skills, try using heatshrink to insulate the wires. Heatshrink is a great way to finish a pair of wires that have been joined by twisting or soldering, and it’s a lot more durable than electrical tape. Wrapping the wires in electrical tape is fine at first, but eventually the tape starts to lose its stickiness and unravel. Heatshrink is also just more fun to use, and you’ll need all the fun you can get when zombies are the only ones knocking on your door.
Heatshrink comes as a tube that you can cut to the length you need. When heated with a hair dryer, hot air gun, or even a cigarette lighter, it shrinks to about half its diameter as if by magic. If your heatshrink starts out with a fairly snug fit over the wires, then it will grip the wires tightly after you heat it.
Here’s how to make a good connection and strengthen it with heatshrink:
1. Choose a heatshrink tube slightly wider than the joint you want to cover. Cut a sleeve long enough to cover the exposed wire and overhang onto the wire’s insulation a little bit.
2. If you’re connecting two wires that already have parts attached to their other ends, slide your heatshrink sleeve onto one wire before you solder them together, pushing the heatshrink as far away from the solder point as possible. I’ve lost count of the number of times I have soldered something together only to remember too late that the heatshrink then couldn’t be slid on. Every time that happens, I have to unsolder the wires again.
3. Join the wires using the end-to-end method described in “Joining Wires with Solder” on page 231. You’ll end up with something like Figure B-8a.
Figure B-8: Applying clear heatshrink tubing over joined wires
4. If you haven’t already done so, slide the heatshrink sleeve over the joint (Figure B-8b). The heatshrink I show is clear so you can see that the solder joint is good. Heatshrink is also commonly available in black and other colors.
5. Heat up the heatshrink with a hair dryer or even a match held underneath it (Figure B-8c). You don’t need to make it super hot. Just keep heating until you have a nice tight fit, as in Figure B-8d. But try not to scorch it!
Heatshrink comes in a huge range of diameters. If you plan to use it, I suggest buying a selection box that has short lengths of various diameters of heatshrink tubing. You can find these at auto parts stores, as heatshrink is often used when modifying or repairing car wiring.
USING A MULTIMETER
An electric current is a flow of electrons. But electrons are small—very small, in fact. So when it comes to working out what’s going on electrically, we need something that will allow us to measure what those pesky electrons are up to.
Where a doctor has a stethoscope to check the various pulse points in your body, an electronics enthusiast will use a multimeter (Figure B-9) to check specific points on a circuit.
Figure B-9: A multimeter
The multimeter shown in Figure B-9 cost about $5 but is still more accurate and has a wider range of features than an expensive multimeter from 20 years ago. Something like it should be perfectly good for any current, voltage, or resistance you need to measure to get ready for the zombie apocalypse.
A multimeter consists of a display at the top, a big rotary switch in the middle to select different measurement ranges, and some sockets at the bottom for attaching test leads. A multimeter should include test leads when you buy it. These are usually of the sort shown in Figure B-10a, but it can be very useful to also get some test leads that have alligator clips on the end (Figure B-10b).
Figure B-10: Test leads
Most auto parts stores will have multimeters, and many places where you can buy tools might well have a multimeter or two. Amazon and eBay also have a huge array of low-cost multimeters for you to choose from, if you want to stock a couple in your apocalypse preparedness kit.