Dwight K. Elvey
dwight.elvey at amd.com
Wed Mar 9 11:24:33 CST 2005
>From: "Jim Battle" <frustum at pacbell.net>
>Ron Hudson wrote:
>> If the desert island has vines you could make a rope computer, as
>> described in a
>> Scientific American, I don't remember the issue.
>It was an april fool's issue, I believe. If memory serves, the island
>was called APRLFUL or something like that. The article showed how, with
>clever arrangements pullies, toggles, springs and such, inverters and
>simple logic gates could be produced. Entertaining enough.
>The problem with that "computer" is that the logic gates have no gain.
>Each gate has no power supply other than the mechanical power of the
>input signals (ropes getting pulled). For instance, say you pull an
>input rope of a NAND gate one foot (OK, let's keep it metric) ten inches
>:-) and the output rope moves nine inches, so the gain is 0.9. Put N of
>these gates in series and the output signal is (0.9**N) of the input
>signal. After half a dozen gates, very little is left at the output.
>The rope gates had a gain much less than 0.9 -- probably 0.5.
>It is the same reason why computers aren't built of of just diodes and
>resistors. You can have a gate or two in series, but then the signal
>needs to be reconditioned before being applied to the next stage.
Relays work great. They have a lot of gain. Maybe much more
than is needed for a computer.
I've always wanted to build a calculator using marbles that
are feed from a hopper and the addition of a manual lever
to work as a clock ( and additional power ).
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