Elenco Electronics EP-130 - Water Level Buzzer

-
146
-
You can use the operational amplifier as
a
c
omparator for detectin
g
chan
g
es in volta
g
e. In thi
s
exper
i
ment, you are go
i
ng to use t
hi
s comparato
r
function to make a water buzzer that sounds when
th
e
wir
e
e
n
ds
c
om
e
into
c
ont
ac
t with w
a
t
e
r.
Slide the switch to
p
osition B, build the circuit, an
d
t
h
en s
lid
e t
h
e sw
i
tc
h
to
p
os
i
t
i
on
A
to turn on t
he
c
ircuit. You should not hear any sound
f
rom th
e
s
p
eaker. Now connect the two out
p
ut terminals wit
h
a wire, and you hear a sound
f
rom the speaker
.
Touch the two output terminals with your
f
in
g
ers. I
f
the speaker makes a sound again, the electricity is
f
lowin
g
throu
g
h your body because the wire lead i
s
i
n contact w
i
t
h
sweat
.
This ex
p
eriment uses two o
p
erational am
p
lifiers. IC
1 works as a comparator. The I
C
’s ne
g
ative (–) inpu
t
terminal has a re
f
erence volta
g
e o
f
about 1.6V. When
a voltage exceeding 1.6V is applied to the positive
(
+
)
in
p
ut terminal, the out
p
ut of the com
p
arato
r
allows IC 2 to work as an astable multivibrator.
N
otes:
EXPERIMENT #124: WATER LEVEL B
U
ZZER
Wiring Sequence:

1-29

2-30

3-114

5-83-80-94-70-110-121

13-86-63-131

14-93-69

65-89-109

66-82-84-91

64-90-92-113

67-81

68-79-85

119-124
Schemati
c