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From: DBG@SLACVM.SLAC.STANFORD.EDU
Newsgroups: comp.theory.cell-automata,sci.electronics
Subject: Re: John Conway's "Life"/Pseudo-Neural hardware implementation
Message-ID: <90309.124445DBG@SLACVM.SLAC.STANFORD.EDU>
Date: 5 Nov 90 20:44:45 GMT
References: <1990Nov1.185409.25802@bradley2.bradley.edu>
Distribution: usa
Organization: Stanford Linear Accelerator Center
Lines: 36

I built a Life implementation in hardware in 1970-71, using a TV display
(black and white) for output and a homemade trackball for input.
The game topology was spiral-wound torus, i.e. the right-hand neighbor
of the bottom right cell is the top left cell. This made it easy to do
all the cell storage in shift registers. I had 19 rows of 25 cells, and
could do a generation in 1/60 second but had a variable hold-off to slow
it down and even stop it. The shift registers had taps in 9 places to
allow counting neighbors, and one extra row-long appendage register to keep
the previous state of the row just updated. Neighbor counting was done with
current summing resistors and comparators, taking advantage of some
nonlinearity in the obvious simple circuit (8 resistors plus diodes
connected to one summing resistor) to spread the 2 and 3-neighbor cases
over the lion's share of the available voltage, so the comparators were
trivially easy.
Oscillators looked very smooth because there was no time-sharing
interference as on the computerized versions of the day, and glider
arrays could fly around and around wrapping forever.
I was in touch with Gardiner (Scientific American) and about to publish
info on it, when I took bad advice and decided to keep it secret so I could
get patents and make a fortune selling it. Dumb idea, as there is no
violence and no simple competitive aspect to keep people interested; the
only market was a very tiny intellectual one, and at that time one would
have had to put a coin slot on it to make it commercially feasible.
My patent application would have been several months after the
Sanders/Magnavox (Using TV for Game Status Display) one, close but useless.

The circuit is either trivially obvious from the above discussion or
completely obsolete because none of the logic devices I used are commercially
available anymore, so don't bother to ask for it. It's not the way you'd
do it anymore--though I suspect it's a better approach than building
discrete physical cells and connecting them together!!!
-- David B. Gustavson, Computation Research Group, SLAC, POB 4349 MS 88,
    Stanford, CA 94309   tel (415)926-2863  fax (415)961-3530
-- What the world needs next is a Scalable Coherent Interface!
-- Any opinions expressed are mine and not necessarily those
   of the Stanford Linear Accelerator Center, the University, or the DOE.