Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 68)

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Take a look at the schematic. Can you guess what kind
of digital gate this is? We’ll use almost the same circuit
here as in the last experiment. Remove the wire between
springs 17 and 20, and the one between springs 16 and
19. Add a wire between springs 17 and 19. Also,
disconnect the 100K
Ω by removing the wire between
springs 19 and 52, we’ll re-connect it later.
Test the four combinations of X and Y to determine the
truth table:
From it, you can see that if X and Y are HIGH then LED1
will be ON. Hence, this configuration is called an AND
gate. X and Y might represent two switches to turn on the
same light in your house, the room switch and the master
switch in the electrical box
. As with the gates we showed
you earlier, you could have more than two inputs by just
adding more parts to the circuit.
Now place the 100K
Ω back into the circuit by connecting
a wire between springs 17 and 52 (not 19 and 52), and
look at LED2. Since you are just adding a NOT gate as
you did in the last experiment you probably know what
the new truth table will look like:
It is a NAND gate, a combination of AND and NOT. X and
Y might represent different trip wires for your burglar
alarm (if either is tripped then that input goes LOW and
the alarm sounds). AND and NAND have the schematic
symbols shown below:
Combinations of AND and OR gates are used to add and
multiply numbers together in computers. The additional
use of NOT, NOR, and NAND gates allows a computer to
represent any input/output pattern you can think of. By
combining these gates with the memory and timing
control that flip-flops provide, today’s computers are
created.
EXPERIMENT #49: This AND That
X Y LED 1
LOW LOW
LOW HIGH
HIGH LOW
HIGH HIGH
AND Gate
Schematic
X Y LED 2
LOW LOW
LOW HIGH
HIGH LOW
HIGH HIGH
NAND Gate