13
The photoresistor contains material that
changes its resistance when it is exposed to
light. As it gets more light, the resistance of
the photoresistor decreases. Parts like this
are used in a number of ways that affect our
lives. For example, you may have streetlights
in your neighborhood that turn on when it
starts getting dark and turn off in the morning.
Visual Volume
Build the circuit shown on the left.
Turn on the slide switch (S1), a police siren is heard. The loudness of the
sound depends on how much light reaches the photoresistor (RP). Try
partially shielding it or placing near a very bright light, and compare the
sound.
Modify the last circuit by connecting the photoresistor to points
A & X. The circuit works the same way but now it sounds link an
ambulance when enough light reaches the photoresistor.
Project 87 Daylight Alarm
Now remove the photoresistor from points A & X and connect it to
points C & Z. The circuit works the same way but now it sounds
like a machine gun when enough light reaches the photoresistor.
Project 88 Bang-Bang Bright
Now connect a 3-snap to make a connection between A & X. Keep
the photoresistor connected between points C & Z. Now depending
on how much light reaches the photoresistor, you will hear either
an ambulance or machine gun sound.
Project 89 Daylight Danger
Now remove the connection between A & X and then make a
connection between B & Y. The circuit works the same way but
now depending on how much light reaches the photoresistor you
will hear either a police siren or machine gun sound.
Project 90
Crooks & Cars
Project 86
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