2
39Switching Basics and More
The concept of switching is fundamental in electronics, and I’m not just talking
about power switches. By “switching,” I mean using one flow of electricity to
switch, or control, another. This is such an important principle that no digital
device can exist without it.
Today, switching is mostly done with semiconductors. Before I deal with them,
I’ll back up and illustrate the concept by introducing you to relays, which are
easier to understand, because you can see what’s going on inside them. And
before I get to relays, I’ll deal with everyday on/off switches, which may seem
very simple—but we have to nail down the basics.
Also in this chapter, I’ll deal with capacitance, because capacitance and resis-
tance are fundamental to electronic circuits. By the end of the chapter, you
should have a basic grounding in electronics and be able to build the noise-
making section of a simple intrusion alarm. This will be your first circuit that
does something genuinely useful!
Shopping List: Experiments 6 Through 11
As in the previous shopping list, you should visit the various online suppliers
for availability and pricing of components and devices. Manufacturers seldom
sell small numbers of parts directly. Check the appendix for a complete list of
URLs for all the companies mentioned here.
Devices
- Power supply/universal AC adapter, 3 to 12 volts at 1A (1,000 mA). See Fig-
ure 2-1. Part number 273-029 from RadioShack, part PH-62092 by Philips,
or similar. - Breadboard suitable for integrated circuits. Quantity: 1. See Figures 2-2
and 2-3. Part 276-002 from RadioShack, model 383-X1000 made by PSP,
part 923252-I by 3M, or similar. A breadboard that has screw terminals
mounted beside it will be a little easier to use but more expensive than
one that does not have terminals.
Figure 2-1. This AC adapter delivers DC
from 3 to 12 volts, and is ideal for electron-
ics projects.In thIs chAPter