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.
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.
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.
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.
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.