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Date: Mon, 21 Jun 99 17:42:54 -0500
From: <dechaze@cardell.com>
To: <lancair.list@olsusa.com>
Subject: Re:annunciators
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>>
Robert N295P(?) asks about availability of LED annunciators...

I have 5 of these in my 360 panel to handle the 3 gear lights, hydraulic pump
transition and header tank overfill.  I have not been satisfied with them
because the LEDs seem to burn out quickly.  Lancair avionics put these in, at my
request, for aesthetics.  I believe the story goes that the factory decided to
remove a resistor in each unit in order to increase the brightness of the LEDs. 
Perhaps the LEDs are not liking the increased voltage they are seeing.  They
sent me spare LEDs which I'm led to believe will be less bright but should
survive.  The factory tech told me I was the first guy to get these installed
and that the factory is not happy with how these units have turned out.  In any
event, I'm now beginning to look for another way to get the job done, perhaps
with real lamps that would fit in the same openning.  Seemed like a good idea at
the time...  Can anyone shed some, um, light on annunciators, (i.e. LEDs vs.
lamps) and perhaps sources?

Best Regards,
Ed de Chazal


[Look in either the Mouser or DigiKey catalog, they have pages of 
LED indicators in all sorts of colors.  If you're worried about intensity
there are many super-bright and ultra-bright LEDs available, but don't
forget to put the current limiting resistor in series with the + side
of the LED.  (Using the current and voltage requirements of a typical
super-bright whose current requirement (If)=25ma and forward voltage (Fv)
requirement is 1.75v, the formula to calculate resistor size is:
(source voltage - Fv) / If.  Using a typical charging system that operates
at 13.6v you would see that (13.6-1.75)/.025 = 474ohms.  Using a 500ohm
resistor for this particular LED would be just fine.)

LED's are really pretty hearty devices when used properly (consider the
several that are on the front of your computer... if you keep your system
on all the time those things will run 24/7/52 for years without fail.)
They are also nice and cool and consume only a fraction of the current
that an incandescent lamp does.  Needless to say, I'll be using all
LEDs on my panel.  Installed with a proper bezel they are readily visible
under all ambient lighting conditions.  Just my $0.02.

   <Marv>     }



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