🚀 go-pugleaf

denny@hpcilzb.HP.COM (Trueman Denny) writes:

>I have a friend who wants to build a arbitration circuit as part of a high
>school project.  Basically all it does is determine who presses a button 
>first just like in Jeopardy.  Does a commodity IC exist that performs this
>function?

>I assume that a debouncing circuit will be needed to give a clean logic
>signal and then some sort of circuit to determine who pressed their button
>first and some sort of LED to indentify the person responding first and
>a buzzer.  If there is a tie then all corresponding LED are energized.

Until very recently, all game shows built these circuits from
relays.  They're easy to understand, very forgiving of bouncing
switches, and allow large voltages/currents to be switched
easily.  12V DPDT or 4PDT relays are ideal.

I believe that the April 1977 (yes, 1977) issue of Popular
Electronics has a design for an SCR-based circuit.  (A variation
on this circuit is what's used in the "Electric Jeopardy" box
game.)

An IC-based circuit would use flip-flops and gates.  A player's
button must be up and the circuit must be in the READY state for
the player's flip-flop to be clocked ON.  Doing this turns the
player's light on and takes the circuit out of the READY state so
that no more players can signal.  Some 555 timers and a speaker
can be used to generate a nice timed square-wave tone.  Since the
first player to press his button clocks his flip-flop and no
other players may signal, bouncing is really not a problem.

Having just built one of these for a pilot for a local TV quiz 
show, let me give you a few more ideas:

On a "real" game show, these circuits usually have three states:  
off, ready, and selected.

In the "off" state, none of the lights are on, and none of the
contestants' buttons are enabled.  The contestants can press
their buttons all they want, but their light won't go on.

Usually after the first half of the question has been read, the
judge puts the circuit into the "ready" state.  This turns on a
light that tells the contestants it's OK to press their buttons.
The next player to press his button gets his light turned on.  A
player cannot be "first" by simply holding his button down; he
must press the button once AFTER the "ready" light goes on.

The "selected" player (his light goes on) is first player to
press his button after the READY light goes on.

All of the lights are cancelled and the circuit goes back into
the "off" state when the judge pushes a "cancel" button.

To get an idea of how this kind of circuit works, watch either
"Jeopardy" or "Trump Card".  Notice how the contestants sometimes
seem to be pressing their buttons before the host finishes
reading the question.  On Trump Card you can sometimes see the
Ready light go on (it's a tiny white light on the right side of
the host's podium).

The extra state is needed in a real game to prevent people from
signaling too early or from keeping their finger on the button.
Allowing ties is not a good idea, unless the game specifically
allows two people to signal at the same time.  Your circuit will
need to have some way of randomly arbitrating between a tie.

Please contact me if you're interested in the designs of these
circuits.
--
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Marc J. Balcer	[balcer@siemens.siemens.com]
Siemens Research Center, 755 College Road East, Princeton, NJ 08540
(609) 734-6531