TTL homebrew CPUs

[Ethan Dicks]

On 7/11/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> > And that 90V battery was probably the single biggest reason why I never
> > built one of those...

Me, either.

> Back when I built mine, 90V batteries were still fairly easy to obtain.
> Nowadays, I'd probably go to the local 'pound shop' and buy 10 cheap 9V
> batteries and link them in series. The current drawn is so low that even
> cheap-n-nasty 9V batteries would last quite a time.

Certainly, that works, but I'd be curious what the lifetime would
be... years?  under a year?

I would think that the shelf-life would be a significant component in
the lifetime calculation, not merely current draw.

I can see how one could make some sort of snap-together 3D battery
sculpture to make a 90VDC brick, but would doing so create some sort
of safety issue?  (discounting grabbing the most negative and most
positive terminals thereby attaching yourself to 90VDC - that is an
implicit safety issue that would still be there if you could find an
old 90V dry battery).

> IMHO it's cheating to use a step-up switching regulator IC. If you've got
> one of those, you can get a 555 timer ;-)

There are plenty of 1970s designs for those - I have them in the Sams
"555 Timer Cookbook", and, I think, in "Don Lancaster's TTL Cookbook"
(he dips into 555 designs as they interface to TTL circuits).  I don't
think there are any listed designs that go up that high there, but
extending what's there isn't too difficult.  One doesn't need a 90VDC
1A power supply for blinking nine neon bulbs.

I may have to dig around my junk box for some bulbs...

-ethan