On 5/27/05, Wouter van Ooijen <wouter@voti.nl> wrote:
> > > 2 You think strobing a 7-seg is time critical?
> >
> > Indeed. You think it is not?
> 
> Indeed. There are somne timing-related aspects that might matter, but it
> does not matter whether the refreshing is done at 200 Hz or 10 kHz.


  Not exactly. Is not time critical indeed (from a software point of
view) but is hardware dependent by the:
1. numbers of digits
2. display quality ( the segment wiewing angle and the segment brightness)
3. segment curent flow 

A 10KHz refresh rate may cause a display to be hard wievable in intense light.
But of course you knew all these.

Vasile 

> 
> > One thing that I discovered when working with those 4-character
> > alphanumeric LED displays from HP (used on a high-end telecom product)
> > was that the slightest variation in refresh timing caused very visible
> > random brightness variations.
> 
> Which type of variation? I find it hard to believe that for instance a
> small change in the frequency is visible att all.
> 
> > All who saw it agreed that it was not
> > acceptable. This was on an 8051-clone, so I ended up doing a
> > "precision
> > reload" of the timer so that the only variation in display timing was
> > the 1 or 2 machine cycles of jitter in the interrupt latency (and zero
> > cumulative error).
> 
> The fact that that solved the probleb does not prove (at least not to
> me) that it was necesarry.
> 
> Wouter van Ooijen
> 
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
> consultancy, development, PICmicro products
> docent Hogeschool van Utrecht: www.voti.nl/hvu
> 
> 
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