OT- sourcing small LED's

I want to put a tiny lightbulb inside a small measuring devise, I'd like
to use a housed LED with a soft flexible line going to a small battery
housing (2 AA's maybe). I've dug around google and found thousands of
things, but nothing like what I'm thinking of.

Anybody have any suggestions?

 

LEDs mostly come in standard packages (eg. 3mm diameter, 5mm
diameter). Check any electronics distributor for the typical
dimensions. You would do well to pick a standard type unless you have
huge quantities.

You can get battery holders with two flexible wires, but you will need
to join the two, and it would probably be wise to have a series
resistor (at a minimum), particularly if the cells are replaceable.

You will be limited in type and color of light with only two cells and
no sophisticated driver circuitry. White and blue leds have the
highest forward voltage.

Using a sophisticated driver chip ($$) and a tiny SMT inductor (or a
more complex but potentially cheaper discrete-based circuit), you can
drive even multiple white LEDs from a couple of cells, even NiMH or
NiCd cells.


Best regards,
Spehro Pefhany

 

I design these types of things on a daily basis...

Depending on actual size, an SMT led should work fine (Digikey -
www.digikey.com or Mouser www.mouser.com).

You MUST use a series resistor (calculate resistor value as follows):

+V(source) - Vf(orward) / I (current through led) = R i.e. 3V-2V (red
led typical) / .020=50 ohm resistor. A 1/8th Watt should be fine.

*Sometimes* you can get away without the resistor, but only for leds
that have a high Vf (like blue or white. White is a blue led with
phospher in it...). On cheap designs using red or green (not typically
blue or white) you can use one resistor for multiple leds, but the
leds should be matched pretty well or you'll get different
brightnesses from the leds (due to current hogging...).

You don't mention if this is for a backlight of a display or just
what, so hard to say what kind of dispersion you will need. If you
give a little more detail, I might be able to offer a more complete
idea of a solution.

Mike Tripoli

 

Thank you for the reply, this is for general lighting inside a 2" tall 1.5"
dia measuring tool base, the operator has to look inside a "window" to align
the product with a blade tip on the measuring devise. Presently we use a lot
of overhead lighting, but this causes a lot of shadows inside the tool base.
White or light blue would be preferred over any color.

I've got an LED probe light at home that's lasted for years, similar to item
#3954T1 here http://www.mcmaster.com/nav/enter.asp?pagenum=648 that's what
got me thinking about this...

Thanks again

I can send you an edrawing if you want to email me...

whit2

at

myway

dot

com

 

Send your edrawing to mtripoli - at - jfww dot com. Is color an issue?
With white leds, they can be tinted one way or another (towards yellow
or blue). You don't really notice this unless you have an array of
them, which in your case it doesn't sound like you do. Shoot me a
drawing and I'll have a look.

Mike Tripoli
www dot jfww dot com

 

You might also look a Lumex.com. They have lots of LEDs and
LightPipes, etc.

Later,

SMA