## Introduction

We will use a breadboard to facilitate the construction of circuits. Figure 1 shows a breadboard where various holes are highlighted with different colors. If two holes share the same highlighted color, they are electrically connected (not all connections are highlighted). This particular breadboard has two rails at the top and bottom. A rail is sometimes called a bus strip or simply a bus. These horizontal lines of holes span the length of the breadboard and are electrically connected. The holes in the top-most rail are highlighted in orange and the holes in the bottom-most one are highlighted in green. In the central area of the board are vertical lines of five holes that are electrically connected. These lines of five holes are known as nodes. There are two groups of nodes, one of which is above the valley and the other of which is below. This valley, which is also called a channel, forms an electrical barrier between the nodes.

In Fig. 1, the red lines represent wires. These wires may be represented as either straight lines, curved lines, or a collection of straight-line segments. Functionally, they are all the same. From an electrical perspective, the only important thing is the location of the end-points of the wire. The wires that appear in the breadboard diagrams can be different colors and the colors themselves carry no inherent meaning. However, it is typical to use black for wires that are at a potential of 0V (ground), while red is often used for a wire that is tied to a positive voltage source.

Two nodes can be connected by inserting the ends of a wire into the holes of the different nodes. On the left side of the breadboard in Fig. 1, a wire has been used to establish a connection between nodes on either side of the valley. The holes of these two nodes are highlighted in light blue. To the right of this, a wire has been used to connect neighboring nodes on the same side of the valley. These nodes are highlighted in red. The holes of the three nodes highlighted in purple have been connected using two wires. The wires we use in the projects will sometimes be called jumper wires or simply jumpers.

Additionally, as demonstrated in the bottom right of Fig. 1, a node can be connected to a rail. In this case, a wire is used to connect one of the nodes to the bottom-most rail. The holes of both the node and rail are shown in green, indicating they are electrically connected.

Figure 2 depicts, using dark gray bars, the underlying electrical connections of the nodes and rails. There are various configurations of breadboards, with different numbers of nodes, rails, etc. But, the underlying electrical connections should always be fairly obvious, provided you understand the configuration described here. If you would like to read a bit more about breadboards, another discussion can be found via the box on the right.