Building Robot Electronics—the Basics—Part II

Making Electronic Circuits—the Basics

You have at your disposal numerous ways to construct the electronic circuits for your robots. Those designs involving only switches and batteries and motors can simply be wired together, one to the other, and there is no need to centralize the components in a single place. Options include:

• Solderless breadboard. Quickly and easily construct circuits by plugging components into sockets on a plastic board. No soldering necessary. See Chapter 32, “Using Solderless Breadboards” for more information.

• Permanent circuit board. Select from among several methods for soldering parts to build a permanent circuit. You can use generic boards that accept common components, or design your own printed circuit board (PCB). See Chapter 33, “Making Circuit Boards” for details.

• Wire wrapping. Use a low-cost tool to interconnect electronic components with very fine wire. See how in Chapter 33.

Understanding Wires and Wiring

Almost every electronic circuit uses wire of one kind or another. Wiring is a science all to itself, but we’ll concentrate just on three main aspects: insulation, gauge, and conductor type.

INSULATION

Most of the wire used in building robot electronics is insulated with a plastic covering. This keeps one wire from touching another and causing a short circuit. Apart from esoteric aspects about insulation, the most important is its color. Get into the habit of using different-color wiring to denote what it’s being used for in your circuit. For example, red wire is often used for the + (positive) battery connection; black wire for the - (negative) connection.

GAUGE

The thickness, or gauge, of the wire determines its current-carrying capabilities. Generally, the larger the wire, the more current it can pass without overheating and burning up.

See Appendix D, “Electronic Reference,” for common wire gauges and the maximum accepted current capacity, assuming reasonable wire lengths of 5 feet or less. When you are constructing circuits that carry high currents, be sure to use the proper gauge of wire. Con- versely, there’s no need to use wires that are way too large for their job. That just makes things bulkier and harder to solder together.

Figure 30-6 Types of hookup wire: solid and stranded. Each has its place. Solid conductor wire is ideal for use with solderless breadboards. Stranded wire is good for general jobs.

CONDUCTOR TYPE

Wire is made of one or more strands of metal, as depicted in Figure 30-6.

• Single-strand wire has just one metal conductor. It’s said to be single stranded, or solid conductor.

• Multiple-strand wire has many conductors and is said to be stranded. For any given wire gauge the conductors in stranded wire are small. When banded together, the individual strands make up the gauge of the wire.

Which is better? Both—it depends on the application. Solid wire is commonly used when building circuits using a solderless breadboard. It’s cheaper to make, so the wire is less expensive. It’s also easier to solder. Stranded wire is more flexible and doesn’t break as easily when it’s repeatedly flexed. It can also carry a bit more current, per gauge, than solid conductor wire.

How to Solder

Few electronic projects can be assembled without soldering wires together. Soldering sounds and looks simple enough, but there’s a bit of science to it. If you are unfamiliar with soldering, or you need a quick refresher course, read the primer on soldering fundamentals provided in this section.

SOLDERING TOOLS YOU NEED

Good soldering means having the proper tools. If you don’t have them already, you can pur- chase them at RadioShack or most any electronics store. Let’s review the soldering-related tools you need.

Stand

If your soldering pencil doesn’t come with a stand, be sure to get one. They’re used to keep the soldering pencil in a safe, upright position. You should never simply lay a hot soldering pencil down on your work table.

Sponge

Keep a damp (never dry) sponge by the soldering station. Be sure to keep it wet. Use the sponge to wipe off globs of solder that may remain on the tip. Otherwise, the glob may come off while you’re soldering and ruin the connection. In a pinch, you can substitute a wetted and folded-up paper towel or napkin. Be sure it stays wet—you don’t want it to catch fire when you try to clean the soldering tip against it!

NOTE: We’ve already introduced the soldering pencil earlier in the chapter. See Figure 30-7 for a description of the pencil’s main parts. Be sure to get one with a three-prong power cord. This provides important grounding of the tool, which is needed for safety.

Figure 30-7. Parts of the soldering pencil. Be sure yours is a three-wire grounded model. Don’t use an ungrounded soldering tool for electronics work. The replaceable tip is a good feature. When it’s worn, you can get a new tip rather than a whole new soldering pencil.

Solder

Use only rosin core solder approved for use in electronic circuits. It comes in different thick- nesses. For best results, use the thin type (0.050??) for most of your electronics. Don’t use acid core or silver solder on electronic equipment. (Note: Certain “silver-bearing” solders are avail- able for specialty electronics work, and they are acceptable to use.)

For noncommercial applications, you have the option of lead-bearing or lead-free solders. Both are safe to use when handled properly, but even the lead-free type can be toxic if ingested. Lead-bearing solder is a bit cheaper and easier to work with, as it has a lower melting temperature.

Miscellaneous Soldering Tools

And there are a few more soldering tools worth mentioning:

• A heat sink looks like a small metal clamp. It’s used to draw heat away from components during soldering.

• Ordinary household isopropyl alcohol makes a good, all-around soldering cleaner. After soldering, and when the components and board are cool, clean the board with rosin flux remover.

• A solder vacuum (or “solder sucker”) is a suction device used to remove excess solder. It is often used when desoldering—that is, removing a wire or component from the board, so that you can fix a mistake.

CLEANING THINGS PRIOR TO SOLDERING

Before soldering, make sure all parts of the connection are clean. If you’re soldering a com- ponent onto a printed circuit board, clean the board first with warm water, a kitchen scouring powder, and a nonmetallic scrubbing pad. Rinse thoroughly, and let dry.

Next, wet a cotton ball with normal household isopropyl alcohol and wipe off all the con- nection points. Wait a minute for the alcohol to completely evaporate, then start soldering.

SETTING THE CORRECT SOLDERING TEMPERATURE

A soldering tool with a temperature control is often referred to as a soldering station. If that’s what you’ve got, and you’re using traditional lead-bearing solder, dial the station to between 665°and 680°F (352° to 360°C). This provides maximum heat while posing the minimum danger of damage to the electronic components.

If your soldering pencil/station has just the control and lacks a heat readout, initially set it to low. Wait a few minutes for it to heat up, then try one or two test connections. Adjust the heat control so that solder flows onto the connection in under 5 seconds.

Note: To do its job, your soldering tool needs to be significantly hotter than the melting point of solder. Most lead-bearing solders have a melting point of about 362°F (183°C). For lead-free solder, the range is much wider, but in general their melting point is 40° to 70°F higher. Increase the temperature of the soldering tool accordingly.