On Sunday, June 29, 2008 9:23 AM [GMT-3=3DCET],
Olin Lathrop  wrote:

> Tom=E1s =D3 h=C9ilidhe wrote:
>> Exactly, I'll multiplex them one LED at a time. This way, I'll have no
>> need for drivers at all.
>
> Only if you can tolerate very dim LEDs.  If each LED will only be on for a
> short time, the current during that short time will need to be large to
> get the same average current.  For example, if you have 50 LEDs with
> never more than one on at a time and you want 10mA average for a LED that
> is lit, then you'd need 1/2 amp thru the LED during the brief time it is
> on.  You have to look carefully at the maximum instantaneous current spec
> for the LED.  You would probably exceed it with your propsed scheme.
>

...One tip.
  During the developing you would like to use a current limited power
supply.
I just forgot a flag in my sw and, after switched on, the micro hanged
(hung?) up in a column.
The green LEDs have turned into red and one of them puff-ed up.
When you are really sure your LEDs sequence is all rigth you can feed up the
circuit with more current.
An LM317 can do the job.

;)
Dennis


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