Elenco 130-in-1 Electronics Playground - Manual (Page 104)

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A microphone can be used to detect sound. Here you
will make a circuit that lights the LED when the
microphone detects sound, using the speaker as a
microphone.
Slide the switch to position B and construct the
circuit. When you finish the wiring, by sliding the
switch to position A to turn on the power. Now talk
into the “microphone” (the speaker) or tap it lightly;
the LED blinks.
Observe the schematic. IC1 is configured as a non-
inverting amplifier with a gain of about 100, and it
amplifies the signal from the microphone (the
speaker). IC2 is configured as a comparator,
comparing the output of IC1 to a reference voltage
from the battery. When IC1’s output exceeds the
reference voltage, the comparator output goes low,
and the LED lights.
Notes:
EXPERIMENT #85: VOICE-CONTROLLED LED
Schematic
Wiring Sequence:
1-29
2-30
3-110
5-76-74-80-70-121
85-31-63-132
33-64
79-65-112
73-86-66
90-67-111
89-68-115
69-109
75-116
119-124
122-131