seven segment display history
cclist at sydex.com
Thu Feb 28 17:57:23 CST 2008
On 28 Feb 2008 at 15:26, Jules Richardson wrote:
> (I was just looking at a museum's mock-up of the Apollo mission control
> console, and the fake readout is made to look like a 7-seg display; I'm just
> surprised that the digital readouts weren't all Nixie-based back then)
7-segment displays go back to the 60's at least--I seem to recall
seeing a prototype 60's EL display using the technique. The RCA
Numitron was about 1970, but it was by no means the first.
I strongly doubt that 7 segment displays were used anywhere in the
Apollo program for a very good reason--their failure mode. If a
Nixie is bad, it doesn't light at all. If a single segment fails on
a 7-segment display, the result can be an ambiguous reading with no
indication of failure. For example, if the top segment fails,
there's no way to distinguish between a 4 and a 9 in most displays.
I think that the Apollo technology was neither incandescent 7-segment
nor Nixie gas tube. I suspect, rather, standard projection displays,
where a strip of film in the form of a loop is placed in front of a
light source. They were modular and very easy to replace from the
front of a panel.
See, for example, the following photo from the Apollo 11 mission:
(warning: it's big (558K). You can clearly make out the numeric
displays (and the half-filled ashtrays) on the ops consoles.
BTW, there are many very good photos at
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