Experiment 23: Nice Dice
214 Chapter 4
Experiment 23: Nice Dice
This is the one experiment where I want you to use the 74LSxx generation of
the TTL logic family, instead of the 74HCxx family of CMOS. Two reasons: first,
I need to use the 7492 counter, which is unavailable in the HC family. And sec-
ond, you should know the basic facts about the LS series of TTL chips, as they
still crop up in circuits that you’ll find in electronics books and online.
In addition, you’ll learn about “open collector” TTL chips such as the 74LS06
inverter, which can be a convenient substitute for transistors when you want
to deliver as much as 40mA of current.
The idea of this circuit is simple enough: run a 555 timer sending very fast
pulses to a counter that counts in sixes, driving LEDs that are placed to imitate
the spots on a die. (Note that the word “die” is the singular of “dice.”) The coun-
ter runs so fast, the die-spots become a blur. When the user presses a button,
the counter stops arbitrarily, displaying an unpredictable spot pattern.
Dice simulations have been around for many, many years, and you can even
buy kits online. But this one will do something more: it will also demonstrate
the principles of binary code.
So, if you’re ready for the triple threat of TTL chips, open collectors, and binary,
let’s begin.
You will need:- 74LS92 counter such as SN74LS92N by Texas Instruments. Quantity: 1 if
you want to create one die, 2 to make two dice. - 74LS27 three-input NOR gate such as SN74LS27N by Texas Instruments.
Quantity: 1. - 555 timers. Quantity: 1 if you want to make one die, 2 to make two dice.
- Signal diodes, 1N4148 or similar. Quantity: 4, or 8 to make two dice.
Seeing Binary
The counter that we dealt with before was unusual, in that its outputs were de-
signed to drive seven-segment numerals. A more common type has outputs
that count in binary code.
The 74LS92 pinouts are shown in Figure 4-101. Plug the chip into your bread-
board and make connections as shown in Figure 4-102. Initially, the 555 timer
will drive the counter in slow-motion, at around 1 step per second. Figure
4-103 shows the actual components on a breadboard.
Note that the counter has unusual power inputs, on pins 5 and 10 instead of
at the corners. Also four of its pins are completely unused, and do not connect
with anything inside the chip. Therefore, you don’t need to attach any wire to
them on the outside.