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Electronics Projects

       Project Prep

Breadboarding

A breadboard is a temporary place to build and test a circuit for an electronics project. You don’t have to solder the circuit; just insert components and the wires, connecting them into handy little holes. When you’re sure you have your circuit right, you can create permanent boards by soldering or by ordering printed circuit boards.

The anatomy of a breadboard

The breadboard itself is a plastic board with strips of metal running underneath and holes in the top. You slot the little wire legs that sprout from components and also the connecting wires into these holes, which contain metal channels called contacts. The metal strips that run underneath connect the items you plug into the holes to each other and the battery.

Breadboards come in various sizes; however, no matter what the size, the top and bottom rows of contacts on the breadboard (see Figure 4-7) are linked horizontally, and you’ll typically use them to connect to your battery.

figure 4-7

How to figure out what size breadboard to get? Some have as many as 3,200 contact points! But don’t overdo. For the projects in this book, we used boards with 400 contact points for small circuits and 830 contact points for medium circuits; for our large circuits, we hooked two boards together with the handy ridges and notches on the sides of the boards.

Notice the + and – (negative) signs on the breadboard. The positive battery terminal is connected to the rows with the + sign; these rows are often referred to as the +V bus. The negative battery terminal is connected to the rows with the – sign; these rows are often referred to as the ground bus. Because the +V bus and the ground bus run the entire length of the board on both sides, you need to use only a short piece of wire to reach a +V or ground bus from anywhere on the breadboard.

Other contacts on the breadboard are linked vertically in rows of five; the five points are connected electrically by metal strips. Most folks place chips in the middle of the circuit, straddling the little aisle with each pin of the IC in a contact hole. That way, each pin of the IC is electrically connected to four other contacts, making it easy to connect other components to IC pins. Don’t fry your board! These things are very susceptible to heat. Shorted components can melt them. Check the components with power on to make sure that nothing overheats. Also, they are designed only for low-voltage DC projects, so don’t apply too much juice.

Figuring and finessing the layout

How you arrange items on a breadboard won’t look exactly like how you’ve arranged items in a schematic. You have to pay attention to a few issues when laying out components on your breadboard. The schematic shows the elements of a circuit and connections, but a breadboard is arranged to make the most efficient connections possible using the holes and connectors available.

Here are some tips to keep in mind. Pin numbering: ICs have pins that are numbered counterclockwise, starting at a little notch or dot indicator (see Figure 4-8). You should place all ICs pointing in the same direction. This helps you avoid inserting an IC backwards and also helps you keep track of the pin numbers. Use various pins, as specified on the IC datasheet, to connect to +V, ground, and other components.

figure 4-8

Neatness counts: Take your time to make your board neat and tidy. This helps you to avoid mistakes and also helps you to troubleshoot if things aren’t working quite right.

Spacing: Leave yourself room to place items, allowing a little space between them. It’s better to leave a little more space between elements and use a bigger or expanded breadboard than to crowd yourself too much. This gives you the space to modify and refine your circuit.

Jumps: Minimize the jumps that you make between connections. (Typically, this involves using a jumper wire.) For example, if you can insert one lead of a component in the same row as the lead of another component you’re connecting to, you don’t have to use a jumper wire to connect them. The less wiring you have, the less messy things get.

Using color-coded wiring helps you to keep track of your layout. For example, many people use black wire for ground and red wire for power. Put wires at 90° angles, not on the diagonal, because diagonal wires will get in the way of other components to be placed on the board. Also keep wires to a practical length: that is, long enough so you can route them around ICs but short enough so you don’t have lots of extra wire cluttering up your breadboard. (Routing wires around ICs means that if you have to remove or replace an IC, you don’t have to remove all the wires as well!)

Assorted lengths of prestripped wires are available that save you time in cutting, stripping, and bending wires to length. You just pick one that’s already cut to the right length. However, each length of these wires is a different color; thus, if you use prestripped wires, you can’t color-code your circuit. Because most of the photos in this book are black and white, we went for the convenience of using prestripped wires rather than color-coding the wires on the breadboard.

Inserting wires and components

In a nutshell, here’s how to wire a breadboard:

1. Use 22 gauge solid wire to make connections (see Figure 4-9). Don’t use stranded wire because it can get smushed when you push it into a hole and could even cause shorts in your circuit if a piece of wire breaks off. See the sidebar, “When stranded wire works,” for times when using stranded wires is more appropriate.

figure 4-9

2. Measure how long of a wire you need to make each connection.

3. Strip off 1⁄4" of insulation from each end. Better yet, buy prestripped wires.

 

4. Bend the bare wire at a right angle.

5. Insert the wire into a hole in the board.

The schematic shown earlier in Figure 4-6 is shown translated onto a breadboard in Figure 4-10. You don’t see the potentiometer, microphone, battery, switch, or speaker on the breadboard because these are connected through wires attached to the five terminal blocks (TB). The sole purpose of a terminal block is to provide a place where you can attach wires to your circuit board by inserting them into holes and using a screw to clamp them down.

Notice that we inserted a lead from C2 into a contact in the same row as Pin 1 of IC1, thereby making electrical contact. We ran a wire from the same row as the other lead of C2 around IC1 to Pin 8 of IC1. This produces a lot neater board than you get when you loop wires over the IC.

Notice also how all the wires are flat on the breadboard. We cut them all to the length required so they didn’t have excess wire poking up in the air. We measured the resistor leads so that we had enough length to cross the distance between the contacts and still have about 1⁄4" more on either side to bend down and insert in the breadboard holes.

figure 4-10

We bent the wires on the ceramic capacitors at a 45° angle so that the face of the capacitor is visible. That way, you can easily read the value of the capacitor on the board. We cut the leads of the electrolytic capacitors to about 3⁄4" to minimize how far they stick up in the air.

When you use a breadboard, you can use and reuse components for different projects. However, be aware that the little contact wires on components can break off easily. If you remove ICs, use an IC extractor or the flat end of a small screwdriver to pry the IC up at both ends, or you will damage it and probably end up tossing it. The leads on ICs aren’t designed to be bent more than once or twice, or they will break off.