Homebrewing a digital computer

From: ajp166 <ajp166_at_bellatlantic.net>
Date: Sun Nov 12 17:58:34 2000

From: Frank McConnell <fmc_at_reanimators.org>
>
>(He's keeping the display digits though.) Each digit is a box with a
>bunch of tiny incandescent bulbs mounted in the back; each bulb
>illuminates one layer of plastic at the front; these layers are
>stacked and each has a digit (or other symbol, e.g. decimal point)
>etched in it (as a bunch of etched dots). There's a diagram on the
>side of each digit-box that indicates which bulb illuminates which
>digit or symbol.


These were common in the 60s. Driving nixies has one problem
you need a transistor that can handle at least 60-80V, early
transistors werent cheap (those that could). Also you needed
high voltage (170-220Vdc) for nixies, plus resistors for current
limiting all adding up to to a lot of space power and heat. Transistors
that could switch 100ma_at_6V were common and cheap so the
same diplay idea was used.

There were other reasons with respect to readability and diplay color
as well.

Another config that was used is a 7segment where each segment was
a wedge of plastic forming the bar and a lamp (or later led) behind it.
These preceded the LED based 7 segment at low cost.

For those that don't know there were also filliment based 7segment
displays (have a bunch) for the early growing display market. They
were aimed at the problem of good leds at that time being expensive
and not terribly bright. My first freq counter has four of these and
still works 27 years later.

>Anybody got any ideas about this thing? His speculation is that
>somebody didn't want to pay for nixies (but he's amazed at what these
>things must have cost to build in comparison), mine is that they
>wanted something nicer than a column of digits 0-9 with a bulb behind
>each.


You are closer to right.

Allison
Received on Sun Nov 12 2000 - 17:58:34 GMT