Hi James.

I'd guess a "High Brightness" red - the highest brightness available
in the size you can squeeze in. But optimum colour will vary with
viewing conditions. The resistor value may be able to be changed from
4k7 to increase the current if you know the forward voltage drop of
the LED. I'm (again) guessing that the max current is 1mA. So if you
have a white LED with a 3.4V voltage drop, the minimum resistor value
would be (5-3.4)/1mA =3D 1.6k - a 1k8 would be a good fit.
Eyeballs are most sensitive to green, so it might be worth looking at
those ones as well.

 I guess (again!!)  you can't flash it to make it more visible - you
used to be able to get leds with a built-in flash circuit. Not sure if
they are still around.

RP

On 6 September 2012 12:25, James Newton <jamesnewton@massmind.org> 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
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
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