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.

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.

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).

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.

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.

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.

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.

Integrated circuits — commonly known as ICs — are like social directors for components: They gather lots of other components in a single location

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.

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

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.

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.

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.

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