27 Nov
2003
27 Nov
'03
3:52 p.m.
> > > Is it that easy to mod the TTY? Where
do you get the relay?
> >
> > The instructions for doing this are in at least one DEC printest,
similar
> > instructions are in the Intel MCS8i manual,
and doubtless elsewhere.
>
> I found them. I'd still need relay part number 4915. There are also
some
things called
"thyractors" called for.
IIRC, a thyractor is some kind of overvoltage clamping device. You could
probably replace it with a pair of zener diodes in inverse series, or
with a VDR. >
> > No idea where you'd get the relay these days. I wonder if you could
> > design a solid-state switching circuit that would work, with an
> > opto-isolator on the input
>
> Maybe, if I had specs for the relay. If I had the specs, I might even
be
able to tell
if I have a prayer of delivering sufficient drive current,
I have no idea what the official spec is, but the DEC cards didn't supply
that much current (I would guess at less than 100mA, but that is a guess). > though I'd still prefer to test on real
hardware before having a bunch
of
boards
manufactured.
Agreed.... Pity my ASR33 is almost impossible to get to, or I'd measure
the relay coil current for you (mine has an official DEC modification PCB
in it).
-tony