Elenco Electronics EP-130, Руководство пользователя

Страница: 115 / 160

You know that digital circuits produce high or low (H
or L) outputs (1 or 0). Now we’re going to make a
logic tester that shows 1 for high level (H) and 0 for
low level (L) on the LED display.
Slide the switch to position B and assemble the
circuit. When you finish the wiring, turn on the power
by sliding the switch to position A. The number 0 is
on the display because the test terminal (terminal
13) is at low level when no input is applied. Connect
the test terminal to terminal 122 to apply +4.5V. The
display changes to 1.
Look at the schematic. The dual operational amplifier
works as a comparator. A reference voltage of about
3V is applied to its negative (–) input terminal. When
the input applied to its positive (+) terminal is higher
than this reference voltage, the comparator’s output
level becomes high, turning off the transistor Q1.
Segments A, E, F, and D of the display turn off,
leaving 1 on the display.
Notes:
EXPERIMENT #96: LOGIC TESTER
-115-
Wiring Sequence:
o
17-18-19-20-44
o
86-79-63-21-23-45-132
o
43-80-82
o
67-81
o
68-83-85
o
119-124
o
122-131
o
69-89-13-CHECK POINT
o
121-25-70-90-84-14-CHECK POINT
Schematic