Make Electronics

Experiment 23: Nice Dice

218 Chapter 4

Getting back to our project: I want to take the three binary outputs and make

them create patterns like the spots on a die. How can I do this? Quite easily, as

it turns out.

I’m assuming that I’ll use seven LEDs to simulate the patterns of spots on a

die. These patterns can be broken down into groups, which I have assigned to

the three outputs from the counter in Figure 4-108. The first output (farthest

to the right) can drive an LED representing the dot at the center of the die

face. The second (middle) output can drive two more diagonal LEDs. The third

output must switch on all four corner LEDs.

This will work for patterns 1 through 5, but won’t display the die pattern for a

6. Suppose I tap into all three outputs from the counter with a three-input NOR
   gate. It has an output that goes high only when all three of its inputs are low,
   so it will only give a high output when the counter is beginning with all-low
   outputs. I can take advantage of this to make a 6 pattern.
   Note that it’s bad practice to mix the LS generation of TTL chips with the HC
   generation of CMOS chips, as their input and output ranges are different; so,
   the NOR chip has to be a 74LS27, not a 74HC27.
   We’re ready now for a simple schematic. In Figure 4-107 I’ve colored some of
   the wires just to make it easier for you to distinguish them. The colors have no
   other significance.

Figure 4-107. A simpli-
fied schematic shows
how outputs from the
74LS92 counter can
be combined, with
signal diodes and a
single three-input
NOR gate, to generate
the spot patterns on
a die. The wire colors
have no special mean-
ing and are used just
to distinguish them
from each other.

555

timer

C B A

74LS92 counter

Clock input

Binary outputs

NOR

D1

D2

4K7 each

D3 D4

to form these patternsThe groups combine

Each of the three

counter outputs

lights these groups

Special

case to

create

a six

pattern

HI

HI

HI

HI

HI

LO LO

LO

LO

LO

LO

LO

LO

LO HI

LO

HI

LO

Figure 4-108. Binary outputs from the 74LS92

counter can be used to power LEDs arrayed

in groups to simulate the pattern of spots on

a die.