This is only a preview of the July 1993 issue of Silicon Chip. You can view 37 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
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Build this low-cost
quiz game adjudicator
If you’ve ever wanted to risk all the prizes
and go for the cash jackpot, then this is the
project for you. Called the Quizmaster, it
lights a LED & briefly sounds a buzzer to
indicate which of four players pressed the
button first.
By DARREN YATES
Imagine it. You’re sitting down with
two other “brains” in the local Gulargumbone Sale of the Month Championships. You’ve just got to make it
through the 60-seconds “fast money”
and all the prizes are yours –a year’s
supply of toilet paper in your choice
of pastel colours, a $100 gift voucher
at Spud Murphy’s secondhand farm
70 Silicon Chip
machinery depot, all the icecream you
can eat in a week, plus various other
(mainly useless) household supplies.
However, your eyes are firmly fixed
on the cash jackpot which grows by
$2.78 each night.
The compere, in thongs and stubbies, bellows out, “Hey, Raelene!
What’s tonight’s grand total cash bon
anza?” Raelene, regaled in the latest
fashion wear from the local opportunity shop, informs the audience, most of
whom are now asleep with excitement,
“Tonight’s bonanza is $38.75 minus
the cost of the beer. We’ll put the one
minute up on the clock and your time
starts ... now!”
Starting out $4.23 behind your opponent, you charge through the fast
money as if you knew the answers
before the questions were even asked.
It comes down to the last question. You
have to get in first and answer correctly
or you lose the lot.
“What’s the name of Bullhead Jones’
prize pig?” Knowing full well that the
answer is Beethoven, you thrust your
arm towards the heavens, expecting
to be awarded all the prizes.
D5
1N4004
470
16VW
9V
RESET
S5
4
6
100k
12
14
PLAYER 1
S1
3
PLAYER 2
S2
7
PLAYER 3
S3
11
PLAYER 4
S4
15
100k
100k
Q5
BC557
82k
16
100k
100
16VW
47k
10k
3-12V
BUZZER
E
B
5
Q6
BC337 C
B
C
S1
E
1k
S2
S3
S4
R1
IC1
4043
R2
Q2
R3
Q3
Q4
R4
100k
Q1
2
D1
1N914
D4
1N914
D3
1N914
D2
1N914
22k
Q1
BC557
E
B
9
22k
10
22k
1
22k
C
Q2
BC557
B
C
LED1
B
E
C
VIEWED FROM
BELOW
A
K
Q3
BC557
B
E
C
A
A
8
E
K
LED2
A
K
Q4
BC557
B
LED3
A
K
E
LED4
C
K
680
THE QUIZMASTER
Fig.1: the circuit is based on IC1, a 4043 quad RS latch. When one of the PLAYER
buttons (S1-S4) is pressed, the corresponding Q output of IC1 switches low &
turns on its associated PNP driver transistor (Q1-Q4) to light one of the LEDs.
Q5, Q6 & the associated 100µF capacitor are used to drive the buzzer.
Your opponent, whose arm was
broken by a freak and mysteri
ous
accident during the last round, raises
his plastered arm a full second after
your own mighty effort. However, the
compere who unbelievably loses his
glasses just after reading the question,
fails to see your arm rocket upwards
and awards the question and all of the
prizes to your opponent.
And the moral of this sorry tale?
– if the compere had been given a
Quizmaster, this would never have
happened!
Circuit diagram
Let’s take a look at the circuit diagram of the Quizmaster – see Fig.1. As
you can see, it uses a single 4043 IC
(IC1), a buzzer, and a few transistors
and LEDs.
Inside the 4043 are four tri-state
RS flipflops. The reset pins (R1-R4)
are connected to their corresponding
PLAYER buttons, while the set inputs
are tied together and connected to the
RESET button (S5). The circuit detects
which of the four PLAYER buttons is
pressed first and disables the other
three buttons until the RESET button
is pressed.
When S5 is pressed to start the game,
the four set inputs are pulled high and
so the Q1-Q4 outputs at pins 2, 9, 10
& 1 also go high. These outputs drive
PNP transistor stages Q1-Q4 via 22kΩ
current limiting resistors. Thus, when
the RESET button is pressed, transistors Q1-Q4 will all be off and none of
the LEDs will be lit.
IC1’s Q1-Q4 outputs also drive a
4-input AND gate made up of diodes
D1-D4. When all four Q outputs are
high, the output of the AND gate is
also high and thus Q5, Q6 and the
buzzer are all off. This high is also
applied to the commoned side of the
four PLAYER buttons.
Normally, the four reset inputs on
IC1 are held low by 100kΩ pull-down
resistors. However, if one of the player buttons is now pressed, the high
output from the AND gate is fed into
the corresponding reset input and
this causes the associated Q output
to go low. This low then turns on the
associated PNP driver stage to light
the correct LED.
At the same time, the output of the
diode AND gate goes low and this
prevents any of the other switches
The four PLAYER
switches are housed
in discarded 35mm
film canisters. Mount
each switch on the lid
of its canister & feed
the connecting lead
out through a hole
drilled in the bottom.
July 1993 71
10k
PARTS LIST
82k
PLAYER 4
D5
PLAYER 3
9V BATTERY
470uF
IC1
4043
Q6
1
D1
22k
22k
22k
22k
D2
D3
D4
PLAYER 1
RESET
Q1
K
100k
LED1
DC BUZZER
1k
Q2
K
LED2
100uF
Q5
47k
680
100k
100k
100k
100k
PLAYER 2
Q3
K
Q4
K
LED3
LED4
Fig.2: the parts layout on the PC board. Be sure to use the correct transistor type
at each location & take care with the orientation of polarised components. The
pin connections for the transistors & LEDs are shown on Fig.1.
from resetting its associated flipflop.
This means that the remaining player
switches are effectively disabled.
Transistors Q5 and Q6 form a simple monostable circuit which drives
the DC buzzer. It works like this.
When the output of the diode AND
gate switches low (ie, when one of
the PLAYER buttons is pressed), PNP
transistor Q5 turns on and provides
base current for Q6. This turns Q6 on
and so the buzzer sounds.
The 100µF capacitor between Q5’s
emitter and the positive supply rail
now charges via the 1kΩ collector
resistor. As it charges, the current
through Q5 tapers off and the voltage
devel
oped across the 1kΩ resistor
drops. Eventually, after about 0.2s,
it drops below 0.6V and Q6 and the
buzzer turn off.
This means that the buzzer only
gives a brief burst of sound, to indicate that one of the players has
responded. The buzzer then remains
off but the relevant indicating LED
remains on to show which player
pressed his/her button first. Pressing
the RESET button now resets IC1 and
turns the LED off again to rearm the
circuit.
Power for the Quizmaster is supplied by a 9V battery via reverse-polarity protection diode D1. The circuit
draws only a few microamps of current
while in reset mode, so there’s no need
for a power switch.
Construction
All the parts for the Quizmaster,
except for the five pushbutton switch
es, are mounted on a PC board coded
08106931 and measuring 144 x 87mm.
Fig.2 shows the parts layout on the
board.
Begin the board assembly by
installing the 10 wire links. These
should all be as straight as possible,
to avoid possible shorts to other
components. If necessary, you can
straighten the link wire by clamping
one end in a vice and then stretching
it slightly by pulling on the other end
with a pair of pliers.
The resistors, capacitors, diodes
and semiconductors can now all be
1 PC board, code 08106931,
144 x 87mm
1 3-12V DC buzzer
1 9V PC-mount battery holder
5 PC-mount 3.5mm sockets
5 3.5mm plugs
4 rubber feet
5 plastic 35mm film canisters
5 normally-open momentary
pushbutton switches
1 10-metre length of light-duty
speaker cable
1 9V battery
4 self-adhesive rubber feet
2 3 x 10mm-long machine
screws & nuts
3 8BA machine screws & nuts
Semiconductors
1 4043 quad RS latch (IC1)
5 BC557 PNP transistors
(Q1-Q5)
1 BC337 NPN transistor (Q6)
4 1N914 signal diodes (D1-D4)
1 1N4004 silicon diode (D5)
Capacitors
1 470µF 16VW electrolytic
1 100µF 16VW electrolytic
Resistors (1%, 0.25W)
5 100kΩ
1 10kΩ
1 82kΩ
1 1kΩ
1 47kΩ
1 680Ω
4 22kΩ
mount
ed on the board. Be sure to
install the correct transistor at each
location and check that the IC, transistors and capacitors are correctly
oriented. The accompanying table
shows the resistor colour codes but
it’s also a good idea to check them on
a multimeter as some of the colours
can be difficult to decipher.
RESISTOR COLOUR CODE
❏
❏
❏
❏
❏
❏
❏
❏
No.
5
1
1
4
1
1
1
72 Silicon Chip
Value
100kΩ
82kΩ
47kΩ
22kΩ
10kΩ
1kΩ
680Ω
4-Band Code (1%)
brown black yellow brown
grey red orange brown
yellow violet orange brown
red red orange brown
brown black orange brown
brown black red brown
blue grey brown brown
5-Band Code (1%)
brown black black orange brown
grey red black red brown
yellow violet black red brown
red red black red brown
brown black black red brown
brown black black brown brown
blue grey black black brown
corresponding player numbers. This
labelling can be done using transfer
lettering or a suitable marker pen.
Testing
The leads from the momentary contact pushbutton switches are terminated
with 3.5mm plugs & these go to matching 3.5mm sockets on the PC board.
Once these components have been
mounted, install the battery holder,
the buzzer and the five 3.5mm sockets. The battery holder is secured to
the PC board using three 8BA screws
and nuts, while the buzzer is secured
using two 3mm x 10mm screws and
nuts, with two additional nuts used
as spacers. You will have to drill two
mounting holes in the PC board to suit
your particular buzzer.
The five pushbutton switches are
housed in discarded 35mm film
canisters – see photo. All you have
to do is drill a hole in the lid of each
canister to accept the switch, plus an
exit hole in the base of the canister for
the switch lead.
The switch leads can each be run
using two metres of light-duty speaker cable. These leads are terminated
with 3.5mm mono plugs to match the
sockets on the PC board.
Finally, the PC board can be fitted
with four rubber feet and the input
sockets and LEDs labelled with their
To test the unit, plug in the external
switches and install a 9V battery. The
circuit should now fire up in one of
two ways – either with all the LEDs
lit or with all the LEDs off. This may
sound a bit imprecise but the initial
state of the circuit will depend on the
state of the flipflops inside IC1.
If all the LEDs are on, check that they
all go out when the RESET switch is
pressed. Now check that the buzzer
briefly sounds and that the appropriate
LED comes on when one of the PLAYER
switches is pressed. The remaining
PLAYER switches should now have
no affect on the circuit and the LED
should remain on until the RESET
switch is pressed again.
If it doesn’t work, first check that all
components are correctly positioned
and that there are no missed solder
joints or solder splashes on the copper
side of the board. This done, check that
pins 5 & 16 of IC1 are at +9V when the
battery is installed.
If one of the LEDs fails to light, check
its associated driver transistor and
check that the LED has been correctly
oriented. Similarly, if the buzzer fails
to sound, check the circuit around
transistors Q5 and Q6. In particular,
note that Q5 is a PNP type while Q6
is an NPN type so don’t get them
SC
mixed up.
Fig.3: this is the full
size pattern for the
PC board. Check
the etched board for
track defects before
mounting any of the
parts.
July 1993 73
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