TTL homebrew CPUs

[Chuck Guzis]

On 9 Jul 2007 at 23:23, woodelf wrote:

> But with a ka-zillion tunnel diodes you can build the fastest
> computer ever. Well that was what all the hype was about in the
> early 60's.
> Did anyone ever use Junction Fets in computer logic?

I doubt it--the transition seemed to be from bipolar to MOS in 
integrated circuits.  JFETs in digital logic seem to have been 
bypossed.

I've still got my GE tunnel diode (and SCR and Rectifier) manual.  
Lots of interesting circuits, but nothing that could have been 
constructed using other semiconductors at the time.  There are some 
logic circuits in the book, however.

Negistors, it turns out, are pretty easy to build.  There's a web 
site that describes how to make simple ones using a sheet of 
galvanized steel.  "Accidental" negistors by way of point-junction 
devices have probably been reported since the 1920s or earlier.

Another 2-terminal semiconductor that I like is the diac.  Can be 
used for relaxation oscillators, but up until a few years ago, I had 
one hooked in series with the line going to my answering machine.  
The moment the line is picked up at a phone anywhere within the 
house, the answering machine is electrically disconnected and doesn't 
interfere with the call.  Also useful for building simple relaxation 
oscillators--and, of course, triggering triacs.

Cheers,
Chuck




Cheers,
Chuck