Owner manual

-
118
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Do you know what a reset circuit does
?
It activates
other circuits and detects any power fluctuations in
order to
p
revent malfunctions. In this ex
p
eriment, w
e
c
han
g
e the supply volta
g
e to the circuit with th
e
switch. The power to the display portion of the circui
t
is on, or logic high, when the switch is set to positio
n
A; it is off when the switch is at position B. When th
e
c
ircuit has been reset the LED display shows 1
.
Let’s start experimenting. First,
f
inish the wiring an
d
set the switch to position B. Now, with the switch se
t
to B, the
p
ower reset circuit o
p
erates under 6V, and
the three LEDs li
g
ht dimly. The LED display is o
ff
,
meanin
g
that the display circuit is not activated
.
Now set the switch to
p
osition A. You can see th
e
three LEDs li
g
ht bri
g
htly because the supply volta
ge
has been modi
f
ied to 9V. For a moment, the LED
display still shows no chan
g
e, indicatin
g
that th
e
c
ircuit is being reset. A
f
ter a short interval, the LE
D
displa
y
s 1 to show that the circuit has finishe
d
resett
i
ng an
d
now
i
t
i
s sta
bili
ze
d.
S
et the switch to position B to switch the power bac
k
to 6V. You will observe the 1 on the LED disappear,
because now the displa
y
circuit is off
.
S
tud
y
the schematic to understand how the circui
t
works. The o
p
erational am
p
lifier is a com
p
arator. Th
e
3 LEDs are connected together to make a re
f
erence
volta
g
e of about 5.4V for the ne
g
ative
(
–
)
terminal.
With the switch in position B, the positive
(
+
)
terminal
receives about 4.1V, so the comparator does no
t
a
ll
ow t
h
e
di
sp
l
ay to
ligh
t.
Wi
t
h
t
h
e sw
i
tc
h
i
n pos
i
t
i
o
n
A
, t
h
e
b
attery vo
l
ta
g
e
i
s
i
ncrease
d
to 9
V
, an
d
t
he
100
μ
F
capac
i
tor gra
d
ua
ll
y causes t
h
e comparator
’
s
positive (+) terminal voltage to increase to about 6V
.
When this voltage exceeds the reference voltage o
f
5
.4V, the LED display li
g
hts 1
.
When you set the switch to B, the volta
g
e at th
e
amplifier’s positive (+) terminal dischar
g
es throu
gh
t
h
e
di
o
d
e, so t
h
e vo
l
tage
i
s re
d
uce
d
to 4.1
V.
Althou
g
h this circuit seems very simple (consistin
g
of only one operational amplifier), it is very comple
x
and im
p
ortant
f
or later use
.
N
o
t
es:
EXPERIMENT #
98
: RE
S
ET
C
IR
CU
I
T
Wiring
S
equence
:

2
1-2
3
-
6
7-11
6

8
5-7
0
-
38
-
2
5-
121

31
-
68
-7
4

3
2-34

3
5-
3
7

73-81-63-129-132

86
-
82
-
69
-
11
5-
130

1
19-124

122
-
131

1
23-133
S
chematic