CHAPTER 14 ■ VARIABLE RESISTORS
■ Note Thorough readers with good memories will dredge up my advice not to purchase or use components
containing the element cadmium. Despite my research, I haven’t been able to locate a suitable replacement
photoresistor without cadmium. “Well, it’s not got much cadmium in it.”
Cadmium-sulfide can be abbreviated CdS. Sometimes, photoresistors are called photocells or
photoconductors. It’s the same component no matter the name.
Potentiometers change resistance in response to rotations of their dials, whereas photoresistors change
their resistance in response to the amount of light shining on them. Pretty cool!
Obtaining Assorted Photoresistors
Encapsulated photoresistors (see Figure 14-12) are available for outdoor or rugged uses. An opaque metal
case and clear plastic lens protect the sensor against moisture, dust, and soil. The opaque metal also
prevents light coming from the rear from affecting the resistance.
Figure 14-12. Encapsulated and exposed ceramic cadmium-sulfide photoresistors
Figure 14-11. Standard cadmium-sulfide photoresistor