How can a tic-tac-toe machine be wired from only a power source, wire, nine toggle switches and eighteen...
competition/games/tictactoe.machine New
New entry, edited from material collected for the archive and not yet in a released version.
Problem
How can a tic-tac-toe machine be wired from only a power source, wire, nine toggle switches and eighteen light bulbs? Many years ago I saw an article in a magazine that showed how to make a machine that played tic-tac-toe using only a power source, wire, nine toggle switches and eighteen light bulbs (no relays or other electronic components). The machine (playing "O") would play against a human opponent (playing "X"). The human opponent would always have to move first by flipping the toggle switch in the lower left corner. This would light the "X" bulb in the lower left cell and also light the "O" bulb in the center square. As long as the human opponent played intelligently (i.e., played legally and blocked any two-in-a-rows), the machine would play properly and ensure a draw (except after the human's final move, then two bulbs would be on in one cell, perhaps indicating the draw). Can someone reproduce how the machine was wired? The toggle switches were all single pole-single throw (SPST). -- Carl G. <cginnow@mindspring.com>
Show solution
Given that restriction, four of the remaining spaces are pretty easy:
Top Left: X in Top Left, O in Middle Left
Middle Left: X in Middle Left, O in Top Left
Bottom Middle: X in Bottom Middle, O in Bottom Right
Bottom Right: X in Bottom Right, O in Bottom Middle
Two of the remaining ones are just slightly more difficult:
Top Middle: X in Top Middle, O in Middle Right
Middle Right: X in Middle Right, O in Top Middle
The last one is problematic. To force a draw, one of the Middle
spaces must be played. But perhaps one has been played already?
It turns out this isn't a problem -- the Top Right space may only be
played as the second or the last move. If the O is placed in Bottom
Middle or Middle Left, a conflict occurs. So the machine must be
wired to place an O in Top Middle or Middle Right.
Top Right: X in Top Right, O in Top Middle
OR
Top Right: X in Top Right, O in Middle Right
This implies that at least two of the switches must be of the DP
variety, the rest may be simple SPST switches.
The last two (given):
Bottom Left: X in Bottom Left, O in Center
Center: Master switch
-- Matthew T. Russotto <russotto@pond.com>
[ Editor: Carl G. then added that the toggle switches were all SPST, and
that he had built one using only SPST switches. ]
Remember I said that the top right square may be the second move or
the last. If it is the second, it should light the top middle or
middle right. Unfortunately, that square is also lit by another X,
and with SPST switches, that X will get lit also in a straightforward
configuration. The only way I see around this is to resort to
series-parallel configuration
GND--TRX--TRSW+-MRO--V
+
GND--TMX--TMSW+
or
GND--TRX--TRSW+-TMO--V
+
GND--MRX--MRSW+
TRX: Top Right X light
TRSW: Top Right Switch
MRO: Middle Right O Light
TMSW: Top Middle Switch
TMX: Top Middle X light
TMO: Top Middle O light
V: Switched power
GND: Ground
This implies that all the other switches should be wired in series,
e.g.
V--CO--BLSW--BLX--GND
rather than
V--BLSW+-BLX-+GND
+-CO--+
so the brightness is consistent.
-- Matthew T. Russotto <russotto@pond.com>
The person who designed the tic-tac-toe machine had a very simple
solution to the top-right square problem. I will let you think about
what it may have been (it didn't require a series-parallel
configuration) and then, if you request it, I will give you their
solution. From a practical viewpoint, I think your solution of using a
couple of DPDT switches would have worked just as well if not better.
-- Carl G. <cginnow@mindspring.com>
[ Editor: the designer's own solution was not among the collected
postings. ]