seven segment display history

Chuck Guzis 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:

http://www.hq.nasa.gov/office/pao/History/alsj/a11/ap11-S69-
39815HR.jpg

(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

http://www.apolloarchive.com/apollo_gallery.html

Cheers,
Chuck




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