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394 COMMON ELECTRONIC COMPONENTS FOR ROBOTICS

Table 31- 3 Capacitor Dielectric Materials (and Their Uses)

Dielectric Typical Applications Polarized*
Aluminum electrolytic Power supply filtering; electrical noise filtering Yes
(decoupling)
Tantalum electrolytic Same as aluminum electrolytic, but smaller and Yes
more compact; more expensive; breakdown
voltages may not be as high
Ceramic Most common; inexpensive, general purpose; No
often referred to simply as a “disc capacitor”
due to its typical shape
Silver mica High precision, typically used for high- frequency No
applications; expensive
Polyester (or Mylar) Low- power, low- frequency signal applications No
polypropylene where ceramic capacitors are not adequate;
more stable than ceramic capacitors
Paper foil Your grandpa’s Heathkit radio No (but better ask
Grandpa)

* Typical. There are exceptions to everything, including whether a capacitor is polarized. So be on the lookout for any
polarization markings, or the lack thereof. For example, some aluminum electrolytic capacitors are nonpolarized. These are
usually marked NP, and are designed for special applications, such as use in stereo speaker systems.

the ubiquitous LM555 timer IC, for example, there’s always a capacitor that— when com-
bined with at least one resistor— determines the duration of the timer.

Diodes

The diode is a rudimentary form of semiconductor. Diodes (see Figure 31- 14) are used in a
variety of applications, and there are numerous subtypes. Here is a list of the most common
that are used in the field of robotics (many of these topics are covered more fully in the proj-
ects found in Part 8):
• Rectifier. Let’s call this the “average” diode. It’s so called because one of its principal uses
is to rectify AC current to provide DC only. It’s used for many other things, too, and is
frequently employed in robotics circuits for motor control applications.
• Schottky. Special kind of diode that has improved performance. Used for applications
where speed, low voltage drop, and “snap action” are needed.
• Zener. This diode limits voltage to a predetermined level. Zeners are used for low- cost volt-
age regulation.
• Photo. All semiconductors are sensitive to light, but photodiodes are made especially for
the task. Photodiodes and their close cousin, the phototransistor, are frequently used as
light sensors in robotics projects.

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