Elenco Electronics EP-130 - Operational Amplifier Blinking LED

-9
7-
N
ow you
’
re
g
o
i
n
g
to ma
k
e a
bli
n
ki
n
g
LED
c
i
rcu
it
usin
g
an operational ampli
f
ier. In this experiment, a
n
LED continuously lights and turns off slowly.
Slide the switch to
p
osition B and connect the wire
s
for this circuit. When you finish connectin
g
th
e
p
roject, slide the switch to position A to turn on th
e
p
ower. After a couple seconds, you’ll see the LE
D
s
tart to blink. Watch care
f
ully and you should be able
to observe that it’s on and o
ff
periods are abou
t
e
q
ual
.
The operational ampli
f
ier works as an astable
multivibrator at low
f
requency. You can alter th
e
p
eriod of oscillation
(
the LED blinkin
g
rate
)
by usin
g
different values for R and C. See what happens to
the blinkin
g
rate when you make the value o
f
R
220k
Ω
k
k
.
O
ne last thing - the operational amplifier has high
input resistance at its inputs - so there is very littl
e
current
f
lowin
g
into its inputs. This means you ca
n
operate
i
t to
b
u
ild
accurate
bli
n
k
ers an
d
t
i
mers w
i
t
h
longer intervals.
No
t
es
:
EXPERIMENT #78: OPERATIONAL AMPLIFIER BLINKING LE
D
S
chematic
Wirin
g
S
equence:

8
1-
3
1-
63
-1
3
1

33
-
6
7-
90
-
94

93-68-113

69
-
8
2-
8
4-
89

83
-7
0
-114-121

1
1
9
-124

122
-
132