Random Number Generator Based Game

This electronic game is
simulation of one-arm bandit game. Electronics hobbyists will find it
very interesting. When toggle switch S1 is in ‘run’ position, all
segments of 7-segment displays (DIS1 through DIS3) will light up. On
turning toggle switch S1 from ‘run’ to ‘stop’ position, displayed digits
will continue advancing and the final display is unpredictable. Thus
the final number displayed in DIS1 through DIS3 is of random nature. The
speed with which the number in 7-segment display keeps changing on
flipping switch S1 from ‘run’ to ‘stop’ condition slowly decays before
stopping with a random number display. To play this game, one has to
obtain three identical numbers in displays DIS1 through DIS3.

The contestant would score 1 (one) point if he manages to get a
final display of ‘000’, 2 points for getting ‘111’ display, 3 points for
‘222’,… and so on—up to ten points for ‘999’. He should try to score
maximum possible points in fixed numbers of attempts (say, 20 to 25
attempts). Apart from using this circuit as a game for entertainment,
one can use it as random number generator for any other application as
well. The decay time with the given component values is around 15
seconds before the display could stop at a final random number.


Circuit diagram

The circuit comprises clock oscillator built around NE555 timer IC4,
three-stage clock pulse counter built using three CD4033 ICs (IC1 to
IC3), and three 7-segment LED displays (DIS1
to DIS3). In clock oscillator circuit, NE555 timer IC4 is used in a
similar way as a free-running astable multivibrator, the only difference
being the additional capacitor C1 introduced between pin No. 7 of IC4
and junction of resistors R22 and R24. When toggle switch S1 is in ‘run’
position, both terminals of capacitor C1 are shorted by switch S1 and
timer IC4 works as a free-running astable multivibrator. The operating
frequency is in the vicinity of 35 kHz, determined by the value of
timing components.

When toggle switch S1 is flipped from ‘run’ to ‘stop’ position,
capacitor C1 is introduced in the discharge path of pin No. 7 of IC4 and
junction of resistors R22 and R24. At the same time, capacitor C4 comes
in parallel with timing capacitor C3 to change the operating frequency
of the astable from around 35 kHz to around 65 Hz. Now capacitor C1
slowly starts charging as it is connected in the discharge path of the
timing capacitors C3 and C4. The clock frequency of IC4 gradually
reduces and after 15 seconds, when capacitor C1 is sufficiently charged,
the oscillating frequency gradually drops and finally it stops
oscillating. Thus, pin 3 of IC4 becomes low.

Second part of the circuit comprises three cascaded ICs, IC1 through
IC3 (CD4033 decade upcounter cum 7-segment decoder). In conjunction
with three 7-segment displays (DIS1 to DIS3), these form a 3-digit clock
counter. The clock counting speed is dependant upon the clock pulse
frequency of IC4. It is connected to clock input pin 1 of IC1 while chip
enable pin 2 of IC1 to IC3 are held low. Thus all clock counter ICs
advance by 1 for every positive clock transition. Reset pin 15 of all
counter ICs is held low through resistor R25. Thus reset facility is not
used in this circuit. Due to persistence of vision, one can not
distinguish 0-9 counting in DIS1 to DIS3 when the clock frequency is

All 7-segment displays appear to show digit 8, while the red LED1
remains lit continuously, indicating clock counter is in running
condition. On sliding toggle switch S1 from ‘run’ to ‘stop’ position,
the counting speed of individual digits falls immediately due to the
clock frequency changing to around 65 Hz. Now, the counting speed will
be 65 Hz for DIS3, 6.5 Hz for DIS2, and 0.6 Hz for DIS1. This speed of
individual digit counting slowly decays, until the counter stops and
LED1 stops blinking, and the final count (random numbers) are displayed
in DIS1, DIS2, and DIS3.

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