At 01:49 PM 4/23/2004 +0100, you wrote:


>But note the limitations of this method which were explained in the [EE:]
>tagged thread.  This will draw extra current all the time, and your LED must
>have a forward voltage of less thasn 2.5volts (immediately ruling out
>blue/white/purple LED's).

It's pretty marginal with the typical red/green LED as well. As the sum
of the two Vf's approaches the power supply voltage, the "extra current"
approaches infinity as does the sensitivity to small changes in the power
supply voltage (and on resistance of the PIC port).

Example, the sum of Vf's at 10mA for HE red and GaP green is 4.1V
typical at 10mA, 5.1V maximum at 20mA.

If the OP wants to try it out for a hobby application, try around 200/240
ohms in series or 100/110 ohms in series.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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