Experiment 6: Very Simple Switching
54 Chapter 2
FundAmentAls
Basic schematic symbols (continued)
For example, the three LED circuits that I have included in
Figure 2-47 show components in different positions, using dif-
ferent symbols, but all three circuits function exactly the same
way, because their connections are the same. In fact, they
all depict the circuit that you built in Experiment 4, shown in
Figure 1-50.
Often the symbols in a schematic are placed so that the
circuit is most intuitively easy to understand, regardless of
how you may build it with actual components. Compare the
example in Figure 2-48, showing the two DPDT switches,
with the version shown back in Figure 2-35. The previous
one looked more like your bench-top version of it, but Fig-
ure 2-48 shows the flow of electricity more clearly.2K
2K
Figure 2-47. These three schematics all depict the same basic
circuit. It’s the circuit that you built with the potentiometer in
Experiment 4.In many schematics, the positive side of the power supply is
shown at the top of the diagram, and negative or ground at
the bottom. Many people also tend to draw a schematic with
an input (such as an audio input, in an amplifier circuit) at the
left side, and the output at the right. So, “positive voltage”flows from top to bottom while a signal tends to pass from
left to right.
When I was planning this book, initially I drew the sche-
matics to conform with this top-to-bottom, left-to-right
convention, but as I started building and testing the circuits,
I changed my mind. We use a device known as a “bread-
board” to create circuits, and its internal connections require
us to lay out components very differently from a typical
schematic. When you’re starting to learn electronics, it’s very
confusing to try to rearrange components from a schematic
in the configuration that you need for a breadboard.
Therefore, throughout this book, you’ll find that I have
drawn the schematics to imitate the way you’ll wire them on
a breadboard. I believe the advantages of doing things this
way outweigh the disadvantages of being a little different
from the schematic styles that are used elsewhere.220
Figure 2-48. This schematic is just another, clearer, simpler way
of showing the circuit that appeared in Figure 2-35.