From: Spehro Pefhany
Subject: Re: LED flickering problem
X-Newsreader: Forte Agent 1.92/32.572
Date: Mon, 23 Dec 2002 03:45:03 GMT
NNTP-Posting-Date: Sun, 22 Dec 2002 22:45:03 EST
On Mon, 23 Dec 2002 11:00:35 +0800, the renowned "timtt"
>I am working of LED display with microprocessor
>Given 5 I/O pins, transistors and D0-7, I controlled(refresh in a cycled
>order) 5 groups of LED(4 7-seg and 1 group of 8 ultra bright), but even the
>refresh rate is as high as 400 Hz(each refresh 80 times a second already),
>there is still flickering.
>I looked at the datasheet, though higher refresh rate, shorter duration of
>pulse needed, but seems that duty cycle must be larger than 20%(my
>understanding is no matter how high the refresh rate, it's still only 20%
>duty cycle, rite??) so the problem cannot be resolved unless some other
>brand LEDs are being used??
You can just increase the refresh rate to reduce flickering. It
doesn't matter if they are on 20% of 0.01 second or 20% of 0.001
second, they will appear as bright to the eye.
Though, at 80Hz, the flicker should be marginal unless there is
movement such as vibration.
>I am sure this is not insufficient current problem coz if it is static, the
>LEDs are fine. And I tried to drive it with signal generator, seems
>~50-60Hz, already no flickering percepted.
Maybe you have some other problem with your firmware. Put an
oscilloscope on the drive lines and see what's going on.
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