Nice Dice

By Charles Platt

For me, a good construction project should create an object that is fun, functional, and pleasing to the eye — and if it teaches me something interesting along the way, so much the better. I managed to satisfy all these requirements when I designed and built a pair of electronic dice. Although dice simulations have been around for many years, I was able to simplify the project while at the same time making it more interesting.

The basic principle is easy to understand. One shown in the table in Figure 2. chip generates a rapid stream of pulses. A second If Pin 12 drives an LED in the center of the chip counts them and displays each number via an array, and Pin 11 is wired to two diagonally posi-array of LEDs imitating the pattern of spots on a tioned LEDs, and Pin 9 adds the LEDs in the die. At an arbitrary moment, we stop the process to opposite corners, the counter will display all the display one number at random. spot patterns from 1 through 5 in correct numerical

Most dice circuits use a decade counter to do order. I liked the simplicity of this arrangement, the counting, but I went for a 74LS92 chip, which but there was one little problem: when the counter counts in sixes and returns the result in binary begins with 0 on all three pins, it should really code. This may sound uninviting, but it just happens display a 6. To fix this, I needed a NOR gate. to be ideal for a dice display. Computers function with Boolean logic, meaning

Figure 1 (page 71) shows the 74LS92 seen from that they contain many components that take two above. It has 14 pins, of which Pins 9, 11, and 12 are or more inputs and give an output according to a outputs. On each of these pins a higher voltage rep- simple rule. The rule for a NOR gate is that when all resents a 1 while a lower voltage represents a 0. The of its inputs are low, it gives a positive output. chip starts with 0 on all three pins. A chip known as the 74LS27 contains three 3-input

When it receives a timing pulse, Pin 12 counts from NORs (as shown in Figure 3). All I had to do was con-

0 to 1. At the next pulse, Pin 12 carries the 1 over to nect all three outputs from the counter to the three Pin 11 and resets itself to 0. Then it counts to 1 again, inputs on a NOR gate, and then wire the NOR output and then, since Pins 11 and 12 have both reached to light up six LEDs. Figure 2 shows this symbolically. their maximum, they carry a 1 over to Pin 9 and reset The actual circuit is in Figure 4, with components themselves to 0. The binary counting sequence is laid out as you are likely to place them on a bread-

Photography and illustrations by Charles Platt

68 Make: Volume 10