Project 72
Visual Volume
Project 73
Eurosiren Volume
Project 75
Fire-Light
Siren
Project 77
Static Gun
Project 76
Crooks &
Cars
The phototransistor contains material that
changes its resistance when it is exposed to
light. As it gets more light, the resistance of the
phototransistor 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 phototransistor (Q4).
Try partially shielding it or placing near a very bright light, and compare
the sound.
Modify the last circuit by connecting points
X & Q using a 1-snap wire and a 2-snap
wire. Now you hear a European siren when
enough light reaches the phototransistor.
Now add a 3-snap wire
between B & Y. Now you
hear a siren, which
changes to a fire engine
sound when enough light
reaches the phototransistor.
Now shift the phototransistor to
points C & Z, Now depending on
how much light reaches the
phototransistor,
you
will
heareither a police siren or
Now shift the 3-snap wire
from points B & Y to points A
& X. The circuit works the
same way but now
depending on how much
light
reaches
the
phototransistor you will hear
either a machine gun
sound or a different sound.
A
B
C
x
Y
Z
Project 74
Funky Volume
Now remove the connection between points
X & Q, and shift the phototransistor to points
A & X. Now you hear a strange sound when
enough light reaches the phototransistor.
Q
-34-
SC-130_050115.qxp 5/14/15 11:46 AM Page 35
