Page 43 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Semiconductors: Diodes

and Transistors

As we noted earlier, electricity may be considered to be vast herds of elec-
trons migrating from one place to another, while electronics is the science of
controlling these herds. Ever since humans discovered electricity (as opposed to
electricity-in the form of lightning-discovering us), taming the little rascal
and bending it to our will has occupied a lot of thought and ingenuity.
The first, and certainly the simplest, form of control is the humble
mechanical switch. Consider a circuit consisting of a switch, a power supply
(say a battery), and a light bulb (Figure 4-1).
When the switch is CLOSED, the light is ON,
and when the switch is OPEN, the light is OFF.
Switch 4 As we’ll see in Chapter 5, we can actually realize

interesting logical functions by connecting
Light
switches together in different ways. However,
if mechanical switches were all we had to play
with, the life of an electronics engineer would be
fairly boring, so something with a bit more “zing”
Figure 4-1. The simplest
control device is a switch was required. . .

The Electromechanical Relay
By the end of the nineteenth century, when Queen Victoria still held sway
over all she surveyed, the most sophisticated form of control for electrical
systems was the electromechanical relay. This device consisted of a rod of iron
(or some other ferromagnetic material) wrapped in a coil of wire. Applying
an electrical potential across the ends of the coil caused the iron rod to act like
a magnet. The magnetic field could be used to attract another piece of iron
acting as a switch. Removing the potential from the coil caused the iron bar to
lose its magnetism, and a small spring would return the switch to its inactive
state.