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Project #65
Visual Volume
Project #66
Daylight
Alarm
Project #67
Bang-Bang
Bright
Project #68
Daylight
Danger
Project #69
Crooks &
Cars
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.
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.
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.
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.
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.
CM-125_Manual_031514.qxp_CM-125_Manual_031514 4/2/14 12:19 PM Page 38
