Elenco Electronics EP-130, Руководство пользователя

Страница: 149 / 160

You can use the dual operational amplifier as a
comparator for detecting changes in voltage. In this
project, we’re going to use this comparator function
to make a water buzzer that sounds when the wire
ends come into contact with water.
Slide the switch to position B and assemble the
circuit. When you finish connecting the wiring, slide
the switch to position A to turn on the power. You
should hear no sound from the speaker. Now,
connect the two output terminals with a wire. You will
hear a sound from the speaker.
Next, 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 project uses two dual 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.
Notes:
EXPERIMENT #127: WATER LEVEL BUZZER WITH OPERATIONAL AMPLIFIER
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Wiring 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