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