24 May
2005
24 May
'05
2:31 p.m.
From: "James Fogg" <James at
jdfogg.com>
I seem to recall that neon's behave as diodes. I might be wrong.
Hi
As tunnel diodes maybe but not your general purpose diode.
They used the negative resistance characteristics of the neon
lamps to create a 2 state circuit. The difficulty was that
not only did this region drift with aging but it was also
effected by the occasional radioactive particle.
The negative resistance region is small as well, making
it difficult to make circuits that worked.
For logic functions, diodes in general lack the ability
to invert. This is critical for any computing of reasonable
complexity.
Dwight
The site
that had some scanned pages from a book, about using neon
bulbs as logic elements. I planned to read it later, and then lost
it. Anyone seen that site?
You mean the stuff in this zip file?
http://computer-refuge.org/classiccmp/neon_lamp_logic/lamp.zip 
24 May
24 May
5:07 p.m.
For logic functions, diodes in general lack the
ability
to invert. This is critical for any computing of reasonable
complexity.
Although the HP9100 kept the number of inverters as low as possible. OK,
it uses the Q and Q/ outputs of all the 40-odd flip-flops, and I think
there may be the odd inverter on the sideboards, but the main gating
board contains no transistors at all -- just 1000-ish diodes.
-tony
6:55 p.m.
>From: "James Fogg" <James at
jdfogg.com>
>
>I seem to recall that neon's behave as diodes. I might be wrong.
As has been pointed out, and in the whole, neons and diodes are different.
However (and this may be what you are thinking of), they do share a somewhat-similar
heavily-non-linear switching characteristic (switch from high-resistance to low-resistance
at some threshold voltage) which makes them both usable for constructing logic gates: the
circuit of a neon AND or OR gate looks identical to a diode AND or OR gate, with a 1-1
correspondance between diodes and neons. (Other circuit parameters like operating voltages
and resistances differ though.)
The negative-resistance characteristic of neons that Dwight mentions makes it possible to
use them as storage elements also, in different circuit configurations.
HP used them for both purposes in some equipment in the 50s/60s. The HP524C counter uses a
couple of neons for an AND/OR function in the 10MHz counter stage. The HP3430A digital
voltmeter (and other equipment which used the same counting modules) used neons for
storage (4-bit latch) (Tony described the latter some months ago).
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ard＠p850ug1.demon.co.uk -
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