TTL homebrew CPUs

dwight elvey dkelvey at hotmail.com
Tue Jul 10 00:02:28 CDT 2007




>From: "Chuck Guzis" <cclist at sydex.com>
>
>On 9 Jul 2007 at 18:45, Dave McGuire wrote:
>
> >    Relaxation oscillators are fun.  I like the UJT version as well,
> > though UJTs are getting harder to find than they once were.  I have
> > two or three 2N2646 UJTs left.
>
>I've still got about a dozen tunnel diodes sitting unsued in my desk
>drawer.  One of these days, I'm going to do something with at least
>one of them.
>
>Cheers,
>Chuck

Hi
For those that want to play with the concept of a Tunnel Diode, one
can make a almost TD using two junction fets. You need a p and a
n channel fet. Place them such that the sources are crossed to the
gates. They will then act like a TD except that they will completely
turn off as the voltage increases. For the smaller TO-92 type fets,
they'll peak at around 1 to 1.5 milliamps. They will oscillate up to
a couple hundred Hz.
I built a FM jammer with a small trim cap, two fets, a coil, variable
resistor , bypass cap and a 9 volt battery.
For logic functions, they can be made into a stable two state element
by stacking 2 of these. One will have the higher voltage across it
while the other will have the lower voltage.
If you really want them to act like a TD, place a resistor in parallel
to give the final slope. It doesn't make them any better at doing
fun things but is closer the a real TD.
Dwight

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