Spacewar! (was Re: Laser display...)

From: Tom Jennings <tomj_at_wps.com>
Date: Sun Feb 20 18:16:05 2005

On Sun, 20 Feb 2005, Jim Beacon wrote:

> You can also get some useful digital functions from analogue circuits -
> Tektronix time mark generators use a non-retriggerable monostable to achieve
> a divide -by-10 function with 4 tube elements (two of those are diodes) -
> how many transistors would we use to build this in bistables?

Then there's the phantastron circuit, with which you can count a
pre-determined number of pulses, with one tube! It's a bit flakey
the more pulses you want to count... 2, 3, 4 is about it.
Basically it charges up a capacitor, uses positive feedback and
peculiar tube cahracteristics.

Fred Williams (aka FC Williams), of "Williams Tube" fame, came up
with the name. Apparently he was quite a guy. I've always wanted a
T-shirt with this picture of him I have, in a suit and holding up
a CRT to eye level with a big grin while giving a talk, with a
quote of his under it:

         "Cheap memory is not fast, and fast memory is not cheap!"

Took a long time for him to become wrong.

> built a protoype divider using a single thyratron to achieve a similar
> division ratio with a total component count of 6 - though you could consider
> the thyratron a true digital device, the details are here
> www.g1jbg.co.uk/thyrdiv.htm

Cool! You're in good company! :-)
Received on Sun Feb 20 2005 - 18:16:05 GMT