■ PHOTO 1.
by John L. Brittan
In the mid-1950s, I was asked to be one of
three judges to participate in a Bible Quiz.
The judges stood in the back of a high
school auditorium. The quizzers were on
stage sitting on chairs. The judges had to
hold a 4x5 inch card in front of their eyes in
such a way that the top edge would be
above the heads of the quizzers. When a
question was asked by the quiz Master, the
contestants that knew the answer would
jump up. Two out of three judges were to
decide who jumped first. You guessed it. It
was an impossible task.
After that evening, I decided to work out an electronic
method to determine who jumped first using NE-2H neon
lamp characteristics. I knew that the neon lamp needed to
see 90+ volts to fire. After firing, the voltage would drop to
55 volts. I concluded that putting lamps in a parallel switch
configuration should work as the first lamp switched ON
would not allow the others to fire since the 90+ volts
would be only 55 volts. Take a look at Figure A. The 30K
ohm series resistor is needed to limit the lamp current to
about two milliamperes.
Problems with this circuit came about when
quizzers jiggled around on their seat switch or if the
first quizzer to jump decided to sit back down. Their
switch would still open, their lamp would go out,
the voltage would go back to 90+ volts, and fire
I have been involved with quizzing for over 50 years.
Of all of the quiz boxes I have constructed, the quiz box
presented here is my best design. The TestMaster Quiz
Box is portable using only three AA cells ( 4. 5 volts). It has
no moving parts (relays) except the hand switches, and no
digital circuitry with the exception of the 10 second 555
timer and several other timing circuits. There is a 10-hand
switch storage compartment, a provision for two or more
quiz boxes to be connected together (no limit), and 10
LED lights and a buzzer signal for when a hand switch has
been depressed (see Photo 1).
This hardware project uses an analog biasing method
to lock out all but the first response in such a way that it
is impossible for a tie to occur (see Circuit Theory). Seat
switches are complicated to make, so I chose to make a
simple hand switch using a pushbutton switch and 3” x
1/2“ O.D. PEX water pipe.
The silicon controlled rectifier (SCR) is used as the primary device to latch the circuit ON, causing lockout of the
rest of the hand switches. Figure 1-a shows the schematic
of the SCR transistor. Instead of using base, emitter, and
■ FIGURE A.
■ FIGURE 1.