Elenco Snap Circuits SOUND &reg - Manual (Page 52)

Listen to the
Light Change
Project 78
The color LED actually
contains separate red, green,
and blue lights, with a
microcircuit controlling them.
Each time the LED changes
colors, the voltage across it
changes. Each time the
voltage changes, you hear a
“click” from the speaker.
Project 79
Adjustable Listen to
the Light Change
Project 80
Bright or Loud?
Turn on the slide switch (S1). The color
LED (D8) changes colors in a repeating
pattern, and you hear a clicking sound
from the speaker (SP2).
Turn on the slide switch (S1). Set the
lever on the adjustable resistor (RV) for
different brightness levels on the color
LED (D8). The color LED is bright on a
more limited range of RV settings than
in the preceding project, and the
speaker (SP2) is not nearly as loud.
Now push the press switch (S2); the
LED is dimmer but the sound is louder.
Turn on the slide switch (S1). Set
the lever on the adjustable resistor
(RV) for different brightness levels
on the color LED (D8). You also
hear a clicking sound from the
speaker (SP2).
The transistor (Q2) amplifies the
LED current, to make the speaker
(SP2) sound louder.
When S2 is off the transistor
(Q2) has little effect, and the
circuit is similar to project
46. With S2 pressed, the
transistor acts as an
amplifier, increasing the
current through the speaker.
The LED current is lower in
this arrangement.
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