19 Sep
2007
19 Sep
'07
10:37 a.m.
J. Peterson wrote:
Well, leave it to Don Knuth to dig up a much older
reference. While
browsing his web pages, I noticed a reference to patent 974,943 by F.W.
Wood, issued in 1910(!). It describes an electro-mechanical "Illuminated
Announcement and Display Signal" with a segmented display. Wood
actually uses eight segments (so his "4" has a slanted top), but other
than that, it's exactly the same design as the digits today's cheap
watches and calculators.
I could imagine there being an even older purely-mechanical analogue to be
honest; perhaps with segments that could rotate and were white on one side and
black on the other, against a black background.
It wouldn't be particularly complex to do (a few pushrods and a bunch 'o cams)
and would take up a lot less space than the 'reel of numbers + viewing window'
of the day. Not suitable for miniaturisation, but easily workable for large
display signs.
However, I'm not sure when the 'airport'-style displays with a reel of flaps
containing the digits (or letters) appeared; they'd be about as compact as a
mechanical seven-seg display, but with less maintenance requirement...
cheers
Jules