Specifications

CONSTRUCTION
DIGITAL NUMBER
SHOOTING GAME
M
any electronic video games are
available in the market. But
for those who may prefer to as-
semble the game themselves, a digital
number shooting game circuit is described
here.
A train of single-digit random num-
bers appears on a 7-segment display, and
the player has to shoot a number by press-
ing a switch corresponding to that num-
ber before it vanishes. If he shoots the
number, he scores ten points which are
displayed on the scoreboard. Successful
shooting is accompanied by a beep sound.
The circuit
Fig. 1 shows the block diagram of the
whole circuit. Blocks 1, 2, and 3 consti-
tute the random number generator. Block
4 controls the ten triggering switches and
block 5 checks for any foul play. The score-
board is constituted by blocks 6 and 7,
while block 8 is meant for audio indica-
tion.
Block 9 controls the speed of the num-
ber displayed, the digital counter, the
switch controller, and the foul play
checker.
Clock pulse generator. The sche-
matic diagram of digital number shooting
game is shown in Fig. 2. The Schmitt trig-
ger input NAND gates N1 and N2 of IC
CD4093 (IC1) are used for producing clock
pulses for random number generation.
NAND gate N2, in combination with ca-
pacitor C2 and resistor R2, forms an oscil-
lator to produce pulses. NAND gate N1
and its associated components comprising
capacitor C1 and resistor R1 form another
oscillator, whose frequency is ten times
less than of the former oscillator.
The pulses from the two oscillators
are ANDed by NAND gate N2 to get ran-
dom clock pulses. The output frequency
from gate N2 (pin 4) varies due to phase
difference between the two oscillator fre-
quencies and the period of ‘on’ state of
output from gate N3 (pin 10).
The prototype was carefully watched
for consecutive 150 random numbers gen-
erated by IC2 (and displayed on DIS.1).
No repetition in the order of the numbers
was witnessed but, interestingly, at times,
the same number was repeated thrice.
Random number generator and
switch controller. The output of gate N2
(pin 4) is connected to pin 1 of decade
counter/decoder/7-segment LED driver
CD4033 (IC2). This IC counts and drives
the 7-seg-
ment dis-
play DIS.1.
The control
pulse pro-
duced by
gate N3 ac-
tivates this
display.
The
clock pulses
also go to
decade
counter/de-
coder IC
CD4017
(IC3, pin
14). This IC
controls the
trigger switches. Ten push-to-on swit-
ches designated ‘S0’ through ‘S9’ are con-
nected to the ten Q outputs (pins 3, 2, 4,
7, 10, 1, 5, 6, 9, and 11 respectively) of
this IC.
These Q outputs become ‘high’ one by
one sequentially with every clock pulse.
IC2 and IC3 must count in unison, i.e. for
the number shown in the display the cor-
responding Q output of IC3 should be
‘high’. For the numbers 0 through 9, the
Q0 through Q9 outputs of IC3 respectively
must become ‘high’. For this purpose, the
‘carry out’ (pin 5) of IC2 is connected to
the reset pin 15 of IC3 through a
differentiator circuit comprising resistor
R4 and capacitor C3.
During the transition from 9 to 0, the
state of ‘CO’ pin 5 changes from ‘low’ to
‘high’ and the differentiator circuit pro-
duces a sharp pulse to reset IC3. Thus, in
every ten pulses, any timing difference, if
present, is corrected. Resistor R3 (470k)
connected in parallel to capacitor C3
quickly discharges it during the low state
of ‘CO’ pin 5 of IC2.
Control pulse generator. NAND
gate N3, along with its external compo-
nents, forms another oscillator of very low
RUPANJANA
A. JEYABAL
Fig. 1: Block diagram of the digital number shooting game
PARTS LIST
Semiconductors:
IC1 : CD4093 Schmitt trigger
quad two-input NAND
gate
IC2, IC5, IC6 : CD4033 decade counter/
decoder/7-segment LED
display driver
IC3 : CD4017 decade counter/
decoder
IC4 : CD4027 dual JK flip-flop
T1, T2 : BC547 npn silicon
transistor
DIS.1-DIS.4 : LT543 common-cathode,
7-segment LED display
Resistors (all ¼watt, ±5% carbon film,
unless stated otherwise)
R1,R2,R4,R6-R9 : 100-kilo-ohm
R3 : 470-kilo-ohm
R5 : 1-mega-ohm
R10-R12 : 1-kilo-ohm
VR1 : 1-mega-ohm pot
Capacitors:
C1 : 0.1µF ceramic disk
C2 : 0.01µF ceramic disk
C3 : 0.001µF ceramic disk
C4 : 0.22µF ceramic disk
C5 : 100µF, 16V electrolytic
Miscellaneous:
PZ1 : Piezo buzzer, continuous
type
S0-S10 : Push-to-on switch
S11 : On/Off switch
: DC IN socket
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