Elenco Electronics EP-130 - Logic Testing Circuit

-
103
-
You know that di
g
ital circuits produce low or hi
g
h
(L
or H) outputs (0 or 1). Now you’re
g
oin
g
to create
a
logic tester that shows 1 for high level (H) and 0 fo
r
low level
(
L
)
on the LED display.
S
lide the switch to position B and construct th
e
circuit. When you finish the wirin
g
, slide the switch t
o
p
os
i
t
i
on
A
to turn on t
h
e
p
ower.
Th
e num
b
er 0
i
s on
the display because the test terminal
(
terminal 13
)
is
a
t low level when no in
p
ut is exerted. Attach the tes
t
terminal-to-terminal 122 to apply +4.5V. The display
a
lters to 1
.
View the schematic. The operational ampli
f
ier work
s
a
s a comparator. The 22kΩ
a
nd 10kΩ resistor
s
produce a reference volta
g
e of 3V at its ne
g
ative (-
)
i
nput terminal. When the volta
g
e at its positive (+
)
terminal exceeds this re
f
erence voltage, th
e
comparator’s output level
g
oes hi
g
h, turnin
g
o
ff
transistor
Q
1. Now se
g
ments A, D, E, and F on the
display turn o
ff
, leaving a 1 on the display.
N
otes:
EXPERIMENT #
8
4: L
OG
I
C
TE
S
TIN
G
C
IR
CU
IT
Wiring
S
equence
:

1
7-
18
-
19
-
20
-
44

86
-7
9
-
63
-21-2
3
-4
5
-1
32

4
3
-
80
-
82

6
7-
8
1

68-83-8
5

11
9
-124

122-1
3
1

69-89-13-CHECK POINT

121-25-70-90-84-14-CHECK POIN
T
Schematic