[Elecraft] Re: PC boards for the K2 RIT-SPLIT LED Mod

[Floyd Sense]

I haven't had the opportunity to check out the recommended LED from Mouser,
but I did order a number of LEDs from Digikey the other day.  Here are some
things I learned after testing last evening.  I used a series pot to set the
current for each diode at 2.9 ma, trying to visualize how noticeable they'd
be looking through a front panel hole.

1. I found the 3mm LED size to have a wider viewing angle than a comparable
5 or 6mm LED.  The light source on those is located nearer to the front of
the LED.  I looked at yellow, red and green samples and the preferred the
yellow.  Digikey part numbers are: Yellow- HLMP1719-ND, Red- HLMP1700-ND.

2. LEDs with a transparent lens had a much narrower viewing angle, although
they were much brighter on axis than those with a diffused lens.  If your K2
will be on a shelf at eye level, a transparent lens will provide a much
brighter alternative.  If you look at your K2 at an angle, the diffused lens
will make the light much more noticeable.  I roughened up a transparent lens
unit with emory cloth just to see if the effect was mainly due to the
diffused lens and found that it was.

3. I checked one of the 28ma. Radio Shack LEDs I had on hand, running it at
2.9 ma.  There wasn't a great deal of difference between that LED and one of
the high efficiency ones in terms of brightness.

5. My favorite LED of the lot for this application is a diffused red high
efficiency unit with a lens diameter of only 1.8 mm, and that part of the
lens extends about 1.8 mm out from a larger square base.  The narrow round
part of the lens would fit into a panel hole of just over 1/16 inch pretty
well.  The Digikey part number for this LED is: 160-1084-ND.

73, Floyd - K8AC

----- Original Message ----- 
From: "Wayne Burdick" <n6kr@elecraft.com>
To: "Bill Flynn AI�C" <qthdotnet@itrweb.net>
Cc: <elecraft@mailman.qth.net>
Sent: Thursday, October 30, 2003 1:44 AM
Subject: [Elecraft] Re: PC boards for the K2 RIT-SPLIT LED Mod


> Bill,
>
> These LEDs may be *rated* at 10 or 20 mA, but how much they actually draw
is
> determined by the series current limiting resistor used. Example: if you
put a 3
> k resistor in series with an LED that drops 2 volts when forward biased,
then
> apply 5 V across them, only 1 milliamp will flow. The forward voltage drop
> changes only a few tenths of a volt over its normal operating current
range, so
> the current drain is determined almost solely by the resistor.
>
> The advantage of "Super bright" LEDs is that they're much more efficient
and
> will actually (in most cases) look much brighter at 1 mA than standard
LEDs.
>
> 73,
> Wayne
> N6KR