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390 COMMON ELECTRONIC COMPONENTS FOR ROBOTICS

Figure 31- 12 How to check the value
of a potentiometer using a multimeter. The
concept is the same as when testing a
resistor. Turn the dial as you test to watch
the resistance value change.

OTHER TYPES OF VARIABLE RESISTORS

Potentiometers are the most common type of variable resistor, but there are several other
kinds you’ll encounter in your robot- building lifetime. The two most often used are photoresis-
tors and the force- sensitive resistor.

• Photoresistors are sensitive to light. Their value changes as the intensity of the light varies.
Photoresistors often go by the names photocell and CdS cell; the CdS comes from cad-
mium sulfide, the mixture of chemicals that make the component sensitive to light.
• Force- sensitive resistors, or FSRs, register force or pressure against them. The resistance
of the component goes up or down as the force/pressure changes. There are numerous
kinds of FSRs used for various kinds of sensing jobs. For example, a flex sensor provides a
varying resistance as it’s twisted or bent. For others, resistance changes as any part of the
membrane of the component is pressed against.
Read more about photoresistors in Chapter 44, “Robotic Eyes,” where you’ll learn how to use
FYI CdS cells to make your robot respond to light. Be sure to check out Chapter 42, “Adding the
Sense of Touch,” for additional details about FSRs.

READING POTENTIOMETER MARKINGS
Unlike fixed resistors, potentiometers aren’t marked with a color code. Instead, their value is
marked either directly— for example, 10,000 or 10K— or indirectly using a decade number-
ing system. In this system the value is a three- digit number such as 503, which means 50,
followed by three 0s, or 50,000. The number is given in ohms, meaning the pot is 50 k .

Capacitors

After resistors, capacitors are the second most common component found in the average
robotics electronic project. Capacitors serve many purposes. They can be used to delay the
action of some portion of the circuit or to remove bothersome electrical noise within a circuit.
These and other applications depend on the ability of the capacitor to hold an electrical
charge for a predetermined period of time.

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