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Running down discrete components: Resistors, capacitors, and transistors

Whereas discreet components should be good at keeping secrets, discrete 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 next section) 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.

Resistors

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 called a potentiometer. 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.

Capacitors

A capacitor stores an 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.

Capacitance is a measurement of a capacitor’s ability to store a charge. The larger the capacitance, the more charge is stored. You measure capacitance in farads (F). 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:

Electrolytic capacitors 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

Axial: These have leads stuck on both ends.

Radial: 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.

Tantalum (a metallic material) bead capacitors 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.

Ceramic capacitors are 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.

Polarized counts

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.

table 1

A final capacitor distinction that we have to make is variable versus fixed. All the capacitors we talked about so far are fixed, 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

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.

figure 3-5

Transistors come in NPN (negative/positive/negative): 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.

PNP (positive/negative/positive): 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 pinout) to determine which pin is which.

ICs

Integrated circuits — commonly known as ICs — 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, zapping). 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 is a dual inline package

(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.

figure 3-6

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 technique called surface mounting. 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 op amps) 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:

LM358: A dual op amp

LM324: A quad op amp

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 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 Pumpkins" use a voice recorder IC.