CHAPTER 14
Variable Resistors
The brightness sensors and balancing dial at the front of Sandwich are variable resistors. In this chapter,
you’ll learn about variable resistors and you’ll prototype the first portion of the line-following circuit. Along
the way, you’ll run across techniques for simplifying schematics.
Thus far, the resistors you’ve experimented with have had fixed values. That is, their resistance stays the
same all the time.
For the LED power indicator circuit, the brightness of the LED is based on the value of the resistor
installed. To change the brightness, you need to remove the resistor and replace it with a resistor of a
different value. It would be nice if the circuit had a resistor that could alter its value so that you could change
the brightness of the LED without having to switch parts.
Potentiometers
Potentiometers (see Figure 14-1) are variable resistors. Their resistance changes by turning a control knob
or dial. You’ve probably operated potentiometers plenty of times without even knowing it. For example,
potentiometers commonly control stereo volume as well as analog television brightness and contrast.
Figure 14-1. A variety of potentiometers