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From: mark@mips.COM (Mark G. Johnson)
Newsgroups: sci.electronics
Subject: Re: Game Arbitration Circuit
Message-ID: <43859@mips.mips.COM>
Date: 6 Dec 90 19:19:30 GMT
References: <1310039@hpcilzb.HP.COM>
Sender: news@mips.COM
Reply-To: mark@mips.COM (Mark G. Johnson)
Organization: MIPS Computer Systems, Inc.
Lines: 66

In article <1310039@hpcilzb.HP.COM> 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.


Here's a suggestion for a gameshow "who hit the button first"
circuit.  It makes a couple of assumptions, namely

     (1) There are no ties.  If more than one player hits
         his/her game button, the first one wins.
     (2) There are three players.
     (3) A solution using 2 chips is OK.
     (4) Switches are SPDT but not debounced.

The logic uses 4000-series CMOS style parts, mostly because they
are cheap and plentiful.  The ICs are U1==CD4043 quad RS latch
($0.63 from DigiKey) and U2 = CD4023 triple NAND3 gate ($0.36).

There are three players labelled A,B,C and one Emcee [Art Fleming]
labelled MASTER.  Each player has a SPDT switch; player A's
switch is connected like this:

        +5.0V ----o
                    /-------> "ButtonA"
          GND ----o/

Player B's and C's buttons are wired the same way, with outputs
ButtonB and ButtonC.  The Emcee's button is used to reset the
circuit (shutting off the LED's) and its output is "MASTERclear".

Player A's LED is attached to the following circuit

                      -------------         LED
                      |           |         |  /|      470 ohms
     ButtonA ---------| R       Q |----+----| < |-----/\/\/\----- +5.0V
                      |           |    |    |  \|
                +-----| S         |    |
                |     |   1/4 U1  |    |
                |     -------------    +------> "QA" to other ckts
                |
                |            (----------
                |          (    4023   |-------< QB
                +--------O(     NAND   |-------< QC
                           (    gate   |-------< MASTERclear
                             (----------

Player B's LED is attached to an identical circuit except that ButtonB
goes in on the left and QC,QA,MASTERclear feed the NAND gate.  Similarly
for player C, ButtonC goes in on the left and QA,QB,MASTERclear feed
the NAND gate.

To use the ckt, the Emcee presses and releases MASTERclear.  This
turns off all three LEDs.  Then after a question, one or more players
hit their buttons.  Whover hit first, has their LED light up.

Note: you will want to finagle around with the value of the resistor
      to adjust the LED brightness and to ensure good I-win-you-lose
      functioning of the NAND gates.

Now someone can translate this into GIF and someone else, into
PostScript.  :-)
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086
	(408) 524-8308    mark@mips.com  {or ...!decwrl!mips!mark}