Elenco 130-in-1 Electronics Playground - Manual (Page 123)

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This circuit changes the intervals between each
sound according to the amount of light falling on the
CdS cell. The sound changes continuously as you
alter the light intensity.
Build the circuit, and set the switch to position A to
turn on the power. The speaker makes a sound. To
change the sound, move your hand over the CdS.
You can calculate the approximate value of the
frequency of the signal by using the equation 1/2 x
C1 x R1. However, R1, in this project, is the CdS and
is not constant. By changing C1 you can change the
value of the output frequency. In this experiment,
another operational amplifier is used as a buffer, so
the light-controlled sound part of the circuit is not
affected by the speaker sound.
Notes:
EXPERIMENT #103: LIGHT-CONTROLLED SOUND
Wiring Sequence:
1-29
2-30
3-64-65
5-86-110-119-124
15-68-109
16-66-67-88
63-131
69-87-85
70-134
121-135
122-132
Schematic