Project 19
Light Controlled
Music
+
Turn on the slide switch (S1) and
you hear a tune. The sound may
stop after a few seconds; if it does,
shine a bright light on the
phototransistor (Q4) to turn the
sound back on. If the sound never
shuts off then cover the
phototransistor. (you may need to
smother Q4 with your hand or take
Use the preceding circuit,
but
replace
the
phototransistor (Q4) with
the press switch (S2). Turn
on the slide switch (S1). A
tune may play for a sh ort
time and then stop. When
there is no sound, push the
press switch (S2) to hear
music; if you release S2
then the music stops.
Project 20
Finger
Controlled
Music
Project 18
Build the circuit as shown. When you
place a metal paper clip across the snaps
on the red & black wires as shown in the
drawing, current flows from the batteries
(B1) through the resistor (R1), through the
paperclip, through the color LED (D8),
and back to the battery. The paper clip
completes the circuit and can current flow
through the LED.
Now replace the metal paperclip with
other materials in your home, and see if
the LED lights. This circuit can be used to
see if a material like plastic is a good
conductor of electricity, or a poor
conductor of it.
Conduction Detector
Materials that have low
resistance to the flow of
electricity
are
called
conductors, and materials that
have high electrical resistance
are called insulators.
-16-
SC-130_050115.qxp 5/14/15 11:46 AM Page 17
