This simple dual digital
dice is based on three low-cost ICs, a few transistors and a handful of
LEDs. IC1a & IC1b operate as an
oscillator with a frequency of about 4kHz and this clocks IC2. The
frequency of oscillation is not critical – it simply needs to be high
enough to prevent cheating. IC2 and IC3 are 4516 binary counters,
configured to count in binary from 1-6. A power-on reset is not required
here since, if the initial state is outside the correct range, the
counters will count into the correct range after a few clock pulses.
Let’s first consider how IC2 operates. When the counter reaches “7” (ie,
111), the AND gate formed by diodes D1 & D2 and the 47kO resistor applies a high to the PE pin (pin 1).
This presets the counter to 1 (ie, 001) and so PE goes low again.
The counter then increments in the normal manner until it reaches “7”
again. Counter IC3 operates in the same manner except that the clock
signal is derived from IC2’s O3 output. The counter outputs (O1, O2
& O3) drive NPN transistors Q1-Q6 and these in turn drive the LEDs (ie, the LEDs indicate the states of the counters). Normally, the counters are incrementing continuously and the LEDs
all appear to be lit. However, when push-button switch S1 is pressed,
pin 6 of IC1c goes low and pin 9 of IC1d pulls the Ci input of IC2 high,
thus stopping the counters. Finally, toggle switch S2 allows the user
to choose between having two dice operating simultaneously or just one.
Author: Len Cox – Copyright: Silicon Chip Electronics