appropriate hole and attaching a 6-32 nut on the other side. See the left side of Figure 6-19 for guidance on how to attach these four standoffs.FIGURE 6-18: Location for drilling holes in the lid of the project box.6 Mount the finger touch contacts on the lid.To make the metal contacts that the user can touch to toss the coin, first insert the threaded end of one of the standoffs through the hole from the top side of the lid, and then screw a second standoff into it from the bottom of the lid. Then attach a 6-32 nut to the threaded end of the standoff that’s beneath the lid. See the right side of Figure 6-19 for guidance on installing these standoffs.Figure 6-20 shows how the box should appear at this point. In this figure, you can see the battery holder and push button already installed in the box, and you can see the standoffs on the underside of the lid.FIGURE 6-19: Installing the standoffs.FIGURE 6-20: The box with the push button, battery holder, and standoffs installed.
7 Mount the circuit board to the standoffs.To complete this step, you must first bend the LEDs around so that they wrap over the edge of the circuit card and then face straight down. Be very careful when you bend the LEDs so that you don’t break the leads or damage any of the solder joints. Figure 6-21 shows what the circuit board looks like when the LEDs are properly turned around.When the LEDs are ready, position the circuit board over the four standoffs. The LEDs should slide right into the two -inch holes you drilled for them in Step 1. If they don’t, just nudge them a bit to make them fit. When everything is in place, secure the circuit board to the standoffs using the 6-32 bolts.FIGURE 6-21: The circuit board with the LEDs turned around.
8 Connect the finger contacts.Attach the free ends of the two jumper wires that are connected to the circuit board to the two finger contacts. To connect each wire, wrap the stripped end of the wire tightly around the threaded part of the standoff. Then, attach a 6-32 nut to the standoff and tighten it with pliers.Figure 6-22 shows what the project looks like with the circuit board installed into the lid and the jumpers connected to the finger contacts.
9 Install the battery.Insert the battery into the holder, and then connect the snap adapter to the battery.
10 Attach the lid to the box.Carefully flip the lid over and secure it to the box using the screws that came with the project box.FIGURE 6-22: The circuit board attached to the lid and the finger contacts connected.
11 Turn it on and toss a coin!You’re finally ready to use the coin-tosser project to help you make decisions. Hold the project box in your left hand and depress the push button with your thumb. Then, touch the index finger of your right hand to the two finger contacts, and watch the LEDs alternate. When you’re ready, let go and see whether the red or green light stays lit.Figure 6-23 shows the finished project.
FIGURE 6-23: The completed coin-toss project.
Chapter 7
The Secrets of Successful Soldering
IN THIS CHAPTER
Soldering is one of the basic skills of building electronic projects. Although you can use solderless breadboards to build test versions of your circuits, sooner or later you’ll want to build permanent versions of your circuits. To do that, you need to know how to solder.
In this chapter, you learn the basics of soldering: how soldering works, what tools and equipment you need for soldering, and how to create the perfect solder joint. You also learn how to correct your mistakes when (not if) you make them.
Keep in mind throughout this chapter that soldering is a skill that takes a bit of practice to master. It’s not nearly as hard as playing the French horn, but soldering does have a learning curve. When you’re first getting started, you’ll feel like you’re all thumbs, and your solder joints may look less than perfect. But stick with it — with a little practice, you’ll get the hang of soldering in no time at all.
Understanding How Solder Works
Before we get into the nuts and bolts of making a solder joint, spend a few minutes thinking about what soldering is and what it isn’t.
Soldering refers to the process of joining two or more metal objects by heating them, and then applying solder to the joint. Solder is a soft metal made from a combination of tin and lead. When the solder melts, which happens at about 700 degrees Fahrenheit, it flows over the metals to be joined. When the solder cools, it locks the metals together in a connection.
Soldering is especially useful for electronics because not only does it create a strong physical connection between metals, but it also creates an excellent conductive path for electric current to flow from one conductor to another. This is because the solder itself is an excellent conductor. For example, you can create a reasonably good connection between two wires simply by stripping the insulation off the ends of each wire and twisting them together. However, current can flow through only the areas that are actually physically touching. Even when twisted tightly together, most of the surface area of the two wires won’t actually be touching. But when you solder them, the solder flows through and around the twists, filling any gaps while connecting the entire surface area of both wires.
