Front panel switches - what did they do?

[Brent Hilpert]

On 2016-May-24, at 11:58 AM, Swift Griggs wrote:
> On Tue, 24 May 2016, Marc Howard wrote:
>> Those aren't LED's on the Apollo display.  They are EL's (Electro 
>> Luminescent displays).  Each segment of each digit was controlled by a 
>> relay.  They astronauts eventually got use to the tinkling sound of the 
>> relays.
> 
> Is that the same as the EL that was used in the 1980's on lots of old 
> stereo gear ? Ie.. you'd hit rewind and some little backlit 
> glass-and-silkscreen template would say "Rewind" in blue or green or etc..
> 
> I LOVE the way that looks. That's one of the reasons why I love the Amiga 
> CD32 (not that I own one.... yet). It looks like a hifi stereo component 
> from the 1980s. I have a Kenwood electronic EQ and spectrum analyzer that 
> has all kinds of EL elements on the front of it. I still use it daily. 
> It's awesome. 


You might be thinking of vacuum-flourescent displays, the green or green-blue displays prevalent on calculators, VCRs, microwave ovens, etc. in the 70-90's (sometimes with some red phosphor). The principle of VF displays is essentially that of a CRT: vacuum bottle with hot filament emitting electrons accelerated to an anode to hit a phosphor to emit light. 

EL (Electro-luminescent) is another technology that more-directly excites the phosphor with an AC supply. No vacuum bottle or hot filament. 
Nowhere near as prevalent as VF.