Other than all the suggestions re: voltage drops, current, etc, I'll add=20
a couple things I've learned from trying to scrape max visibility=20
(rather than brightness) out of LED's while consuming the least amount=20
of power.  First is that it seems that the narrower the viewing angle,=20
the brighter the LED.  You can search digikey for LED's, sort by highest=20
brightness, and run down the list to see what test current they used to=20
get that brightness.  Second is to increase contrast, and that I do by=20
putting some color-matched acrylic over the front on the LED/electronics=20
(assuming you intended this to be on an open PCB).

Cheers,
-Neil.


On 9/5/2012 8:25 PM, James Newton wrote:
> I have a pin coming out of a chip that indicates an error condition. Pin
> will be at +5 or ground. (e.g. not a 3.3 volt system)
>
> The output requires at least 4.7K ohms resistance, or risk pulling more t=
han
> the iMAX rated current for that pin.
>
> PCB already done, no room for a transistor to amplify the output (next
> revision).
>
> So the question is this: What LED would you use to get the most noticeabl=
e
> indication from 5 volts through a 4K7?
>
> I'm thinking very small, but diffuse red.
>
> But then I notice the ones with the highest mcd rating are always clear..=
..
>
> Any experienced advice?
>
> --
> James Newton at massmind.org
> 1-970-462-7764
>

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.