-----Original Message-----
From: Olin Lathrop [mailto:olin_piclist@embedinc.com]=20
Sent: 21 October 2010 13:48
To: Joe P. Farr
Subject: Re: [PIC] Convert number to bit position

Joe P. Farr wrote:
> Depending on how your configure your LEDs, one advantage of=20
> multiplexing could be a power saving as only one LED's on at a time

No, it doesn't work that way.  To achieve the same average brightness,
the single on LED has to be run at much higher current.  For example, if
10mA continuous results in the desired brightness but the LED will only
be on 1/4 of the time, you then need 40mA when it's on.

This is actually worse than the steady case for three reasons:

1 - The higher current causes more heat losses in the LED due to its
resistance.  Or put another way, the voltage accross the LED will be
higher at 40mA than at 10mA even if the average brightness is the same.

2 - There is a upper limit on instantaneous LED current.  This imposes a
lower limit on the duty cycle.

3 - You have to make sure you flash fast enough to appear steady to a
human observer.


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