29 Aug
2008
29 Aug
'08
1:12 a.m.
Ethan Dicks wrote:
I was recently watching "Goldfinger" and
oggling the countdown timer
on the bomb. I don't think I've ever seen that type of display
technology up close, but in principle, it shouldn't be hard to
replicate.
<http://www.vintagecalculators.com/html/calculator_displays.html#Incandescent>
I was thinking that some sort of modern CNC would make short work of
the digit faces - just CAD up some outlines and bang out a few sheets.
Alternately, a pantographic sign engraver might do the trick, with
suitable templates whipped up either by hand on on a CNC.
The compact design for the type marked "KGM M4" looks intriguing as
well - a few slits cut in an aluminum back, and a simple PCB layout
for the bulbs (though I must confess I was contemplating white LEDs
rather than bulbs for a variety of reasons, including longer life
and simpler drive circuits).
As for driving it, I was thinking about something like a '145 O.C.
decimal decoder (as found in Commodore PET keyboard circuits and KIM-1
memory decoder and LED decoder circuits) per display. They aren't
particulalty expensive, and all you'd have to do is pipe in 4 bits and
let the '145 do all the work.
Nixies and other contemporary (and now faded) display technologies
are cool, but any of the glass-envelope types aren't exactly feasible
to reproduce in a home workshop.
Ha! .. funny you should notice that (see the comment at
http://www.cs.ubc.ca/~hilpert/eec/calcs/Canon130.html). I suspect (just a
guess) that the counter in the movie is a mocked up General Radio instrument,
as they made counter instruments using their own version of that type of display.
Rick Bensene's site has some good pictures of the internals of the Canon
version (http://www.oldcalculatormuseum.com/canon161.html).
This idea was discussed on the list sometime ago, and I did a quick experiment
with some plexiglass, forming the digits with a sequence of 'dots' formed by
the end of a drill bit in the plexiglass, and white LEDs, but it was only
moderately successful. I think I was using too-thick plexiglass, and also
concluded that one would need several LEDs per digit, making it quite
expensive, but this was a couple of years ago and white LED's were pricey.
IIRC, the light dispersion of LEDs was part of the problem (that is, they don't
disperse enough compared to incandescents).
Trying to get all the LEDs arrayed around the plexiglass edges with appropriate
light shielding may become an issue. Arrays of bare LED die would be nice..
One of the nice things about using LEDs is heat dissipation wouldn't be an
issue as it was for the original designs with incandescents (note the aluminum
bulb enclosures).
A more considered effort than what I attempted may well be more successful..