Relay computers

[Adrian Vickers]

At 22:50 23/09/2004, you wrote:

>On Wed, 2004-09-22 at 11:17 -0700, Vintage Computer Festival wrote:
> > On Wed, 22 Sep 2004, Jules Richardson wrote:
> >
> > > Apologies if someone's mentioned this one before. Quite possibly the
> > > coolest gadget I've seen in a long time, though:
> > >
> > > http://www.cyberniklas.de/pongmechanik/indexen.html
> >
> > Awesome.  It would be great to get stuff like this exhibited at the VCF.
> >
> > The web page is pretty smart also.  What terrific technical and design
> > work.
>
>Amazing, huh? If I read that right, it's 52 relays though (I don't know
>any German) which makes it sound rather like a 'simple' relay control
>system rather than an actual relay computer. I fired off an email to
>them to see if they'll let me have a nose at the wiring diagrams.

I did some back-of-a-fag-packet calculations (i.e. they might be completely 
& utterly wrong, in which case I'd appreciate corrections) on a relay 
computer...

Assume you want a Z80-type CPU. This has ~8k gates. Typically, it seems to 
take 1 relay per input to implement any given gate. Now, I don't know how 
many "x-input" gates there are in a Z80, so I'll assume that - on average - 
it will require 3 relays/gate. Thus, we need ~24,000 relays to implement 
the Z80.

If each relay needs, say, 25mA @ 6v to operate, then the peak current draw 
of our R80 (as I shall call it) could be around 600A (I think). And that's 
before we've added memory, i/o, etc.

As for the heat/noise - well, IMHO it's worth building it just to 
experience that! Mind you, you'll need a lot of room: If you use 30mm by 
13mm relays, then the board space you need is at least 9.36 square 
metres... Still, if you assume that each board needs approx 40mm of space 
incl. airflow room, then you should be able to fit the R80 into 2 400mm by 
400mm by 2000mm cabinets (internal w/d/h)...

The relays I've been looking at typically quote around 25ms to operate 
(either way), so I don't see how you could clock the R80 at anything faster 
than around 40Hz; and you'd probably want to drop to 20Hz to be on the safe 
side. The same relays quote a typical lifetime of 10e7 operations; so at 
20Hz, your R80 should last a little under 139 continuous hours of operation 
before relays started failing...

Creating a screen driver should be interesting....

Question: Wouldn't it be easier to implement an OR gate with no relays at 
all (just two wires joining together)? Or would you need to use the relays 
to keep the output voltage/amperage regulated?


Cheers,
Ade.