piclist 2002\10\29\165925a >
Thread: Direct LED connection?
www.piclist.com/techref/displays.htm?key=led
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face BY : Russell McMahon email (remove spam text)



> I inadvertently connected an LED directly to RC5 with no current limiting
> resistor.  It is flashing brightly at 1 Pulse Per Second.  The PIC port
can only
> source about 25 mA and that's about right for a bright LED.  Other than
the
> current draw is there any down side to driving the LED directly?

'tis somewhat naughty and you really should check the current to be certain.
This will change with LED type also - eg white LED at 3.5v odd is much nicer
to PIC than red LED at rather less forward drop.

Doing this risks holding the PIC pin at near mid rail where interesting
internal effects may happen. While this is normally more of a concern for
inputs it's not overly wise here.

All that said - this definitely works OK in practice SOMETIMES. YMWV. If
this is for a one off non mission critical application for fun and you don't
mind it self destructing and size is all critical (eg in a brooch or badge
etc) then do it. Otherwise, addition of a resistor is recommended.



       Russell McMahon

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