CHAPTER 14 ■ VARIABLE RESISTORS
The voltage at TP1 and the voltage at TP2 vary based on the amount of light seen by the pair of
photoresistors on their respective sides. Not only does this circuit balance the sets of photoresistors, but it
also converts their variable resistance into variable voltage.
Converting Resistance to Voltage with a Voltage Divider
Combining a variable resistor (such as a photoresistor sensor) with other resistors and taking the voltage
value between them is called a voltage divider. The balanced brightness-sensing circuit is nothing more than
voltage dividers dividing up voltages among bunches of resistors. Along with current-limiting resistors,
voltage dividers are among the most important and most often used techniques within a circuit.
Chips are good at reading voltages. The next time you have a chip and you’d like to connect it to a
variable resistor, think of voltage dividers. And the next time you think of voltage dividers, think of two or
more resistors and measuring in between them.
Building the Balanced Brightness-Sensing Circuit
Assemble the balanced brightness-sensing circuit on a solderless breadboard (see Figure 14-18). Build it
on the far-right side of the board so space remains for the other line-following circuits to be added in the
next chapters.
Figure 14-17. Voltage changes at TP1 when sensors have less light