Neon bulb logic elements link?

[Brent Hilpert]

> >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).