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MC33171:A single op amp

MC33172:A dual op amp

MC33174:A quad op amp

Amplifying sound

Audio amplifiers are similar to op amps except that they are designed to pro-
vide more power; logically, being audio amps, they provide enough power to
drive speakers.

The LM386 is a widely used audio amplifier. Different versions of the LM386 are
designed to work with different supply voltages. For example, the LM386N-1,
which we use in projects in Chapters 6 and 7, is designed to work with a 6 volt
supply and can work with a supply voltage as low as 4 volts. The MC34119 is an
audio amplifier that can work with a supply voltage as low as 2 volts.

ICs are available for many specialized uses; you can see some of them in
action in the projects that we include in this book. The projects in Chapters 11
and 15, for example, use encoder/decoders ICs paired with motor driver ICs.
The project in Chapter 10 uses a timer IC paired with a decade counter IC, and
the project in Chapter 7 uses a speech synthesizer IC paired with an audio
amplifier IC. The projects in Chapters 9 and 14 both use a voice recorder IC.

The switch is on ...................................................................................

A switch seems simple enough: You flick it one way to go on and the other
way to go off. However, understanding what’s happening behind that switch
requires that we give you a bit of background.

Open:A switch is in an openstate when there is no electrical connec-

tion. When switch is open, there is very high resistance between a wire

coming into a switch and the wire going out of the switch.

Closed:A switch is closedwhen there is an electrical connection. When

a switch is closed, there is very low resistance between a wire coming

into a switch and the wire going out of the switch.

There are different kinds of switches, referred to as SPST, SPDT, and DPDT, as
shown in Figure 3-7. Here’s what these catchy acronyms mean:

SPST (single-pole, single-throw):This kind of switch has two lugs to

which you can solder wires. When the switch is on, the two wires are

connected; when the switch is off, the two wires are disconnected. We

like SPST switches so much that we use them as on/off switches in every

project in this book.

SPDT (single-pole, double-throw):This kind of switch has three lugs

to which you can solder wires: one for an incoming wire and two for

Chapter 3: Assembling Your Electronics Arsenal 45