Manual

-146-
Y
ou can use the operational amplifier as a
comparator for detecting changes in voltage. In this
experiment, you are going to use this comparator
f
unction to make a water buzzer that sounds when
the wire ends come into contact with water.
Slide the switch to position B, build the circuit, and
then slide the switch to position A to turn on the
circuit. You should not hear any sound from the
speaker. Now connect the two output terminals with
a wire, and you hear a sound from the speaker.
Touch the two output terminals with your fingers. If
the speaker makes a sound again, the electricity is
flowing through your body because the wire lead is
in contact with sweat.
This experiment uses two operational amplifiers. IC
1 works as a comparator. The IC’s negative (–) input
terminal has a reference voltage of about 1.6V.
When a voltage exceeding 1.6V is applied to the
positive (+) input terminal, the output of the
comparator allows IC 2 to work as an astable
multivibrator.
N
otes:
EXPERIMENT #124: WATER LEVEL BUZZER
Wi
ri
ng Sequence:
o 1-
29
o 2-
30
o 3-
114
o 5-
83-
80-
94-
70-
110-
121
o 13-
86-
63-
131
o 14-
93-
69
o 65-
89-
109
o 66-
82-
84-
91
o 64-
90-
92-
113
o 67-
81
o 68-
79-
85
o 119-
124
o 122-132
Schematic
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