25 Jun
2015
25 Jun
'15
5:15 p.m.
From: Doug Ingraham: Thursday, June 25, 2015 4:10 PM
On Thu, Jun 25, 2015 at 10:22 AM, Vincent Slyngstad
wrote:
I've been thinking lately that whole Omnibus cards could be generalized
that way.
The only other concern I've had during my
thought experiments
along this line related again to the current/power involved. The
device is likely to become difficult to cool if you achieve a 4X
volume reduction.
The easy way to do this is to make one board with a small CPLD connected to
all the pins and program it to match the logic of the card you are
emulating. That way you can have a couple of hundred boards made up for
you at a reasonable cost that are all the same but ends up with different
functionality. Just stick a label on the handle to tell what the card was
programmed as. I don't think you would have heat issues unless
you actually tried to use
the original circuits.
I had assumed, since the subject contains "built from individual transistors",
that something akin to the original straight-8 circuits was what was being
discussed.
Straight 8 signals typically run 8 mA when low and 10 mA when high,
and that's from the -15V supply, per signal. I estimate that's a few
hundred watts for the whole thing. Reducing the supply voltage to
-5V would presumably cut the power (and hence the heat) to a third,
by eliminating most of the waste heat from all the pull-downs.
The Straight 8 logic uses pulses for some things
instead of levels making
it not really compatible with more modern logic. At least not a direct
replacement. The later models would be better targets. An I for example
might be the best choice.
I like the 8/I too, though it's not "built from individual transistors".
You can't shrink the size of the Front Panel
because the switch spacing is
already just a little narrow for people with large fingers. It would be
better to make it a little oversize in fact. I don't have large hands and
it would still be better for me if the spacing was slightly wider.
I completely agree, at least if you're actually going to use the darn
thing a few hours at a time. Some models of the PDP-11 did use much
smaller (still available) switches, but fitted them with honking paddles
to make them more comfortable to use.
Vince