Elenco 130-in-1 Electronics Playground - Manual (Page 126)

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Who says an operational amplifier (op amp) can’t be
used to make a digital circuit? Here, you will use one
to make an AND gate. The LED display is the output
device. If it displays nothing, at least one of the output
signals is logical 0 or low; if it displays H, they are all
logical 1 or high.
When you finish the wiring, turn on the power by
setting the switch to position A. The LED remains
dark. The input terminals are 125, 127, and 129.
These terminals are connected to the negative (–)
terminal, so they do not cause the LED to light.
Terminal 14 is connected to the positive (+) terminal,
so it is the logic 1 terminal. When you connect
terminals 125, 127, and 129 to terminal 14 in various
combinations, you see that the LED lights and shows
H only when terminals 125, 127, and 129 are all
connected to terminal 14 - logic 1.
Notes:
EXPERIMENT #106: OP AMP THREE-INPUT “AND” GATE
Wiring Sequence:
14-85-81-63-19-18-21-22-23-132
25-47
46-88
78-76-83-80-70-48-121
67-87
68-82-84
86-69-126-128-130
129-75-WIRE
127-77-WIRE
125-79-WIRE
119-124
122-131
Schematic