[sdiy] Leaving off a pot?

[scottnoanh at peoplepc.com]

For my Model 2 Klee sequencer, I'm using red LEDs and driving them with just
a little over 2 mA - the brightness is fine.  Not sure if I have low current
LEDs (bought bulk over a year ago), but 2 mA low current LEDs is what I'm
specifiying for it.

Cheers,
Scott

----- Original Message -----
From: "Seb Francis" <seb at burnit.co.uk>
To: "Sam Ecoff" <secoff at execpc.com>
Cc: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, October 08, 2006 7:55 PM
Subject: Re: [sdiy] Leaving off a pot?


>
> >> LEDs have a voltage drop that varies with the color.  So the resistor
> >> value depends in part on what color you choose.
> >
> > Wow. I had no idea. I actually thought of mentioning in my original
> > post that I was thinking of green, but I thought it didn't matter. So,
> > I'd need an LED whose forward voltage was rated at at least 10v, so
> > this should work, right?:
>
> No.  A normal green LED will have a voltage drop of about 2V  That means
> that 8V out of 10V will be dropped across the resistor.  This allows you
> to work out the current through the LED using simple Ohms law.
>
> I=V/R
> e.g.
> I=8V/1K
> I=8mA
>
> Probably a good starting point!  My advice: just try a 1K resistor and
> see how you like the LED brightness.  Different LEDs will have different
> brightnesses.  The voltage drop shouldn't vary very much for a green LED
> - all should be about 2V.
>
> Seb
>
>
>