Re: ATM DIY LED Flashlight Conversion

[Dennis Hoofnagle <dhoof@az.com>]

I converted a couple small solar rechargable yard lights to chart viewing
lights using red LED's.  

As was suggested before, I used the original filiment bulb base by breaking
off the glass bulb (use caution as suggested before) but I preferred to keep
the insulating filler in the metal base below the glass bulb to help
insulate my LED lead (the longer lead which is the anode (+)) as it is fed
through to be soldered at the center contact of the base.  Therefore...no
heating required except to use a soldering iron to remove the solder
connecting the filiments to the base edge and center contact point and
solder the LED leads.

I used Radio Shack's "Jumbo Super Bright" LED's.  (Cat. No. 276-086).
Maximum ratings for these are 2.5 volts at 30mA.  These have an incredible
luminous intensity of 5000mcd (at 20mA)  (Compare that value with the LED's
you were planning to use and you'll find that with this bulb you CAN look
for lost parts on the ground!)  Also, these bulbs are Jumbo, meaning that
when mounted in the old bulb base, it is an almost exact replacement for the
size of the glass bulb. (which should help the flashlight reflector function
as designed).

For intensity control I settled for a Radio Shack Potentiometer of 5k ohms
(Audio Taper) Cat. No. 271-1720.  At that time I was unable to find one that
included an off switch but since the lamps I was converting already had a
on-off switch I settled for these.  With this "pot" I'm able to smoothly
adjust the intensity from very dim to far brighter than you can comfortably
look at. I suspect for a flashlight a slider style "pot" would be preferable
such as I've seen for volume controls on small portable radios.

Another interesting advantage of this particular application was that the
batteries are "C" cell rechargables connected to solar panels for recharge
during daylight hours.  These rechargable batteries are rated at 1.2 volts
vs. the 1.5v of your typical "Duracell".  So I can use the LED rated at 2.5
volts WITHOUT a limiting resistor.  I notice that a AA size rechargable I
have here is rated at 1.25 volts so two of them would just reach the max
tolerable for the LED without a limiting resistor.  Of course, in my
application, the "pot" is acting as a limiting resistor, but necessary only
for my comfort because I can't stand the light at it's brightest! So if you
wished to use rechargable batteries with the LED I've used, you could
probably forget about adding additional resistance in series unless, of
course, there was a real risk you might put in standard batteries by mistake.

I hope this info is helpful for the TN starting this thread.  I've deleted
the original submissions so I don't remember who it was!

Dennis Hoofnagle
Bellingham, WA