Running down discrete components: Resistors, capacitors, and transistors
components should be good at
components are so-named because they are one single,
solitary thing, rather than a collection of components like those contained in
an integrated chip (IC). (Read more about ICs later in
Discrete components are single electrical items, typically resistors,
capacitors, and transistors.
Diodes are also discrete components, but the only kind
we use in this book are light emitting diodes (LEDs). See the later section,
“Let there be light: Light emitting diodes,” for more about these.
The job of a resistor is to restrict the flow of
current, which is essentially the flow of electrons. The more electrons, the higher the
current. For example, you might want to stop LEDs (which love to eat current)
from burning themselves out, and so you would add a resistor to your circuit.
You’ll find these little guys used all the time in electronics circuits.
We measure resistance in ohms, which are so tiny that the measurement of them is
usually given in thousands (kohms) or millions (megohms) of ohms. The
value of a resistor is indicated by colored bands, with each band representing
a number. However, rather than counting colored bands, just read the
packaging your resistor comes in or test it with a multimeter.
One variation on a resistor is a variable resistor, also
A variable resistor allows you to constantly adjust from 0
(zero) ohms to a maximum value. These can be mounted on the face of a gadget,
where you adjust them with a knob; or, you can mount them on a circuit
board, where you have to adjust them by using a screwdriver. A typical use of
a potentiometer is to control the volume of an amplifier in a sound circuit.
electric charge. Quite often, you’ll see capacitors used hand in hand with a resistor — for example, in a circuit
whose job is to set timing. Because it takes time for a capacitor to fill
with a charge, you can set your watch by them (so to speak) if you use a resistor
to control how fast the charge (that is, current) flows in. Also, they make good
filters for DC signals because although AC passes through a capacitor with
ease, DC signals are stopped in their tracks.
is a measurement of a capacitor’s
ability to store a charge. The larger the capacitance, the more charge is stored. You
An F is
pretty darn big, so you have to use prefixes to show lesser
values. The prefixes used are micro- (millionth), nano-
(thousand-millionth), and pico- (the ever-popular million-millionth).
Although you can find several kinds of capacitors —
based on what material they are made of — three common types of capacitors
you’ll run across in electronics projects are electrolytic, tantalum bead,
and ceramic. Here’s are the basic characteristics of each:
are typically made of some kind of
foil material, and you’ll find them with values of 1 microfarad and up.
The two types are
These have leads
stuck on both ends.
These have all
the leads attached to the same end.
We use the axial type for the projects in this book
because they take less room on a breadboard. The value of this type of
capacitor is printed on it along with a voltage rating and its capacitance. Be careful to check the voltage rating required by your
project and choose a capacitor accordingly.
(a metallic material)
are available with values of 0.1 microfarad and higher. They cost more than the
electrolytic capacitors but are useful if you have a circuit that requires more
accuracy because tantalum capacitors have less variation in value
than electrolytic capacitors.
nonpolarized (see the sidebar, “Polarized counts”), and you can find them with values from 1 picofarad to
0.47 microfarad. Reading the value on these tiny components can be
difficult. And to add to the confusion, because many of these capacitors are too
small to write the value on in words and numbers, folks use a code. Table
3-1 helps you spot common capacitor values based on their markings.
Most electrolytic and tantalum capacitors are polarized, so you will see a polarity symbol on them. Typically, only one end is marked with either a plus or minus sign, so you can conclude that the other end is the opposite. With both types of capacitor, the longer lead is the positive one, which is probably the easiest way to identify it.
What’s important about being polarized? If a capacitor is polarized, you have to be absolutely sure to install it the right way around in your circuit. If you don’t, you will be left with one dead capacitor and possible damage to other components in the circuit. Small-value capacitors, typically made of ceramic or mica, are nonpolarized so you can connect them any way you want.
A final capacitor distinction that we have to make is
variable versus fixed. All the capacitors we talked about so far are
meaning they have a set value you can’t adjust. However, variable capacitors can by
adjusted by various methods. We use a variable capacitor, for example, in
"ٍSurfing the Airwaves project"
for tuning a radio.
Transistors are the darlings of the electronics world.
Transistors amplify a signal or voltage, or switch voltage on or off. The
really amazing thing about transistors is how tiny they are: Before the advent of
transistors, people used vacuum tubes to perform the same function, and a vacuum
tube is huge in comparison. Transistors also use a lot less power.
When you shop for transistors, be sure to check the
package type. You can use packages starting with TO, such as TO-92, TO-39, and
TO-220 (as shown in Figure 3-5) in breadboards or manually soldered circuit
boards. Packages starting with SOT or SOIC are meant to be used on huge assembly
lines and don’t have the types of leads that you can use easily in
hobbyist electronics projects.
Transistors come in
You turn on NPN transistors by
applying positive voltage; they start to turn on when you apply
about 0.7 volts. We use NPN transistors throughout this book because it’s
more straightforward to apply a positive voltage to get things working.
You turn off PNP transistors by
applying positive voltage; they turn on when you apply negative
voltages or voltages near ground.
Transistors have three leads: the emitter, base, and
collector. In "Discovering schematics", we show you how to read schematics so you can figure out
where to connect each pin. For each transistor you use, check the
datasheet (which contains a drawing, called a
to determine which pin is which.
Integrated circuits — commonly known as
— are like social directors for components: They gather lots of other components in
a single location
TO-92 TO-39 T0-220
(shuffleboard optional). ICs typically contain a number
of transistors, resistors, and capacitors connected on a silicon chip to make a
functional circuit in one small package.
ICs, as well as some other electrical components, can be
susceptible to electrostatic discharge (in other words,
For that reason, be sure to also get yourself an anti-static wrist strap (as we discuss
in "Static discharge") for your electronics workshop.
ICs come in many packages
Manufacturers make ICs in many types of packages or
containers. (A whole valley in California is dedicated to this type of
thing.) The type of package that you use either in a breadboard or a circuit board
(DIP). A DIP is made up of plastic that encapsulates a
silicon chip, with a row of metal leads running on either side of the plastic.
You insert these leads into the contact holes in a breadboard and connect
components on the breadboard with the circuitry on the silicon chip. (See
the later section, “Breadboard Basics,” for more about this process.)
DIP ICs are identified by the number of leads they have,
such as 8-pin DIP, 14-pin DIP, 16-pin DIP, 18-pin DIP, and so on. Figure
3-6 shows a few common DIP ICs.
When you order ICs, be careful to order an IC in a DIP
package. If you obtain an IC in a non-DIP package, such as an SOIC (see the
earlier section, “Transistors”), you can try forever, but you will never be able to
insert the leads into a board. High-volume manufacturers use these other ICs with a
In this technique, the leads are
soldered onto a contact on the surface of a circuit board, not inserted into a hole. If
you really need to use an IC that comes only in a surface mount-type package, look
for adapters to which you can solder the surface-mount IC and then insert the
adapter into your board.
Because ICs are simply a collection of components (such
as transistors, resistors, and capacitors) stuffed in miniature onto a silicon
chip, each type of IC can perform a different function. That function depends
on how many of each component is placed on the chip and how they are wired
together. The next two sections provide an overview of two common ICs:
operational amplifiers and audio amplifiers.
Opting for op amps
Operational amplifiers (affectionately known as
are a type of IC that contains a series of transistors; each transistor
amplifies the voltage of the signal just a bit more. You could build a multistage
transistor amplifier that could do a similar job by using several transistors,
capacitors, and resistors, but why bother? This setup would use about 50 times more
space on your breadboard than a single 8-pin DIP op amp.
If you look in a catalog for op amps, you’ll probably
see pages and pages of them — they’re that popular. The fact that we’re using 6
volt batteries to power our circuits narrows down the list considerably. Many op
amps are designed to work with a positive supply voltage and a negative
supply voltage, such as +6 volts and –6 volts. We use op amps in our projects that
are designed to work with a 6 volt, or less, single-sided supply. An op amp
that is designed to work with a single-sided supply needs only a positive supply
voltage and ground.
Op amp ICs usually come in 8-pin DIPs; some of these
have one op amp circuit, and some have two op amps
(dual op amps).
In a dual op amp, the pins that give access to one op amp are on the left side of
the DIP, and the pins that give access to the other op amp are on the right
side of the DIP. As you can see in the Murmuring
Merlin project, this allows you to
build one portion of your project circuit along the left side of the
breadboard and a second portion along the right side of the breadboard, which can come
in handy if things get overcrowded. Op amp ICs also come in 14-pin DIPs.
These contain four separate op amps and are therefore called
quad op amps.
Here are some common op amps used in electronics
projects using low-voltage batteries:
A dual op amp
A quad op amp
A single op amp
A dual op amp
A quad op amp
Audio amplifiers are similar to op amps except that they
are designed to provide 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
part of web site . The "Controlling a Go-Kard,
Infrared Style" project, for example, use encoder/decoders ICs paired
with motor driver ICs. The project "Dancing Dolphins" uses a timer IC paired with a
decade counter IC, and the project "Murmuring Merlin" uses a speech synthesizer IC
paired with an audio amplifier IC. The projects "Scary
a voice recorder IC.