Elenco Electronics EP-130, Manual, Page: 119 / 160

This alarm gives out an alarm light and sound when
it detects your voice or any other sound. The
earphone acts as a microphone. Sounds picked up
by the microphone are amplified by IC 1. Diodes Da
and Db rectify the amplified signal - that is, they
convert the sound signal from AC to DC. The signal
travels through IC 2, the comparator, and activates
the LED and the speaker.
When you finish building the circuit, rotate the
control fully counter-clockwise, and set the switch to
position A. Then, rotate the control clockwise while
speaking into the microphone, and set the control in
a position where the LED light only when you speak
into the microphone. Stop speaking and you will see
the LED turn off.
Now, see what happens when you disconnect the
wire between 57 and 62, and reconnect it between
57 and 32. When you blow into the microphone
(earphone), the LED and the speaker sounds.
Notes:
EXPERIMENT #99: SOUND ALARM CIRCUIT
-119-
Wiring Sequence:
o
75-63-28-131
o
29-76
o
30-47
o
31-64
o
46-86
o
56-77-110
o
58-59-60-79-78
o
85-80-61-109
o
66-83
o
67-90-73
o
68-89-71
o
87-69-113
o
74-111
o
84-91-115-127
o
112-129-128
o
49-50-51-53-54-135
o
114-13-EARPHONE
o
122-132
o
27-65
o
57-26-121-130-48-116-70-92-88-62-33-72-14-EARPHONE
o
119-124-134
Schematic