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From: "John Jardine"
Subject: Re: LED flickering problem
Date: Mon, 23 Dec 2002 17:03:30 -0000
NNTP-Posting-Date: 23 Dec 2002 16:50:25 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Spehro Pefhany wrote in message
> On Mon, 23 Dec 2002 14:33:19 -0000, the renowned "John Jardine"
> >Unless you have an incredibly high visual response speed, then a refresh
> >rate of even 20Hz would be sufficient.
> NO.. 20Hz is WAY too slow. Try it (with a numeric display) and see.
> But 80Hz is acceptably fast, with double that being pretty darn good.
> >Sounds like the LEDs when in the 'on state, are not being given enough
> >current to produce the intense, short, bright, flash needed to give the
> >human eye a perception of continuity.
> Drive current doesn't matter other than to establish brightness level,
> there is no effect that is as you describe. The only flicker effect in
> the human eye that I'm aware of is the better perception of flicker
> in the periperal vision. Not a factor here.
> >I.e. As you say, when static, the current is as it should be. But ...
> >being scanned, the current needs to be a lot higher to give more light
> >to balance the shorter time they are 'on'. Essentially the current needed
> >high enough to burn out the LEDs in the static unscanned condition.
> It shouldn't be that high with conservative design practices- under
> typical room-temperature conditions.
> Best regards,
> Spehro Pefhany
> "it's the network..." "The Journey is the reward"
> email@example.com Info for manufacturers:
> Embedded software/hardware/analog Info for designers:
Yes, 20Hz is *very* slow but look at the early calculators where they used
every trick in the book to get the power consumption down. A lot of them
visibly flickered even when viewed straight on and these operated in the
20Hz area. The interupt servicing is a good idea but what drove me was
"I am sure this is not insufficient current problem coz if it is static, the
LEDs are fine".
I would have expected him to mention a very high static brightness as if it
was a problem but he didn't, which is why I pointed up the 'burn out'
I reckon Timptt is seeing "normal" brighness under static conditions.
Hopefully he may report back with his solution but from past observation I'd
say we're all plaiting fog ;-)
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