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'POV - was Multiplexing Seven Segment Displays [OT]'
1997\09\16@120050 by mikesmith_oz.nosp*m

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face
On 16 Sep 97 at 10:49, Martin R. Green wrote:

> Sounds like you are one of those rare souls with a very short
> retinal persistence.  I find no noticeable flicker, or "strobe", on
> any LED displays where all characters are scanned on less than
> 1/30th of a second.
>  You are a prime example of doing "worst case" design, and going for
>  a
> 1/40th or 1/50th of a second full scan.

Supermaket ones drive me crazy.

>
> I have heard of people that get headaches watching commercial movies
> because the 1/24th of a second frame rate flickers dramatically to
> them.

Um, maybe, I don't go often.  I recall sitting thru the entire
StarWars trilogy (when it was first released) - it wasn't my head
that ached - bit lower.

What scan rate do you run your monitor at? (vertical) - Mine's going
nicely at 85 - thats nice to look at straight on.
MikeS
<mikesmith_oz@nosp*m.relaymail.net>
(remove the you know what before replying)

1997\09\16@173357 by Herbert Graf

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-----Original Message-----
From: Mike Smith <mikesmith_oz.nosp*spam_OUTamTakeThisOuTspamRELAYMAIL.NET>
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU <PICLISTspamKILLspamMITVMA.MIT.EDU>
Date: Tuesday, September 16, 1997 12:03
Subject: POV - was Multiplexing Seven Segment Displays [OT]



{Quote hidden}

   Same here, some microwaves aren't great either.

>> I have heard of people that get headaches watching commercial movies
>> because the 1/24th of a second frame rate flickers dramatically to
>> them.
>
>Um, maybe, I don't go often.  I recall sitting thru the entire
>StarWars trilogy (when it was first released) - it wasn't my head
>that ached - bit lower.

   I don't really notice it much in movies, except when there is panning
going on, then it is REALLY bad.

>What scan rate do you run your monitor at? (vertical) - Mine's going
>nicely at 85 - thats nice to look at straight on.

   My monitor only runs at 60, I guess I am one of the lucky ones that
notices it, but it doesn't effect me much, I often am infront of this screen
most of the day. TTYL

1997\09\16@181931 by John Payson

picon face
> >> I have heard of people that get headaches watching commercial movies
> >> because the 1/24th of a second frame rate flickers dramatically to
> >> them.
>
>     I don't really notice it much in movies, except when there is panning
> going on, then it is REALLY bad.

Modern movie projectors flash the screen twice for each frame (resulting in
a 48hz flash rate); 8mm projectors flashed 3x/frame (resulting in a 54Hz
flash).  For stationary pictures, the double-flash helps reduce flicker.  It
has the annoying side-effect, however, that moving images appear "doubled"
and blurry.  If you focus on any light object as it travels across the screen
(and track it with your eye) you'll notice that you see "two" of them while
they are moving.  The same thing also happens on scrolling displays which are
scanned more than once per scroll (the worst is displays that scroll a line at
a time at about 20-30fps); anyone driving scrolling displays with a PIC (or
any other CPU) should keep that in mind.

'Multiplexing Seven Segment Displays [OT]'
1997\09\17@161102 by Martin R. Green

picon face
Actually, I'm convinced that figuring out the optimum refresh rate for a
given screen size and resolution is a black art, too complex for us mere
mortals.  If it looks good to you, the rate must be OK.

As far as lightbulbs go, they are not really affected by flicker because
the hot filaments have a very long persistence.  Fluorescent lights,
however, do pulsate in time with the AC frequency.  This is why those
strobe rings on  LP turntables don't work with incandescent light.  You
need fluorescent or neon illumination to set the turntable speed with this
method.

CIAO - Martin R. Green
.....elimarKILLspamspam.....bigfoot.com

----------
From:   Eric van Es[SMTP:EraseMEvanesspam_OUTspamTakeThisOuTILINK.NIS.ZA]
Sent:   Wednesday, September 17, 1997 3:45 PM
To:     PICLISTspamspam_OUTmitvma.mit.edu
Subject:        Re: Multiplexing Seven Segment Displays

Martin R. Green wrote:

{Quote hidden}

Do you need higher refresh rates, because the monitor has a large area
to refresh?The 7seg would be very small...

> A 50Hz scan should be sufficient for a LED bar, but there is no reason
> you
> can't go to 100Hz if you want.

After all the lightsbulbs in SA all run off 220V 50Hz. Only sometimes
you detect a flicker - usually when there's a power dip. I suppose it's
because the filament does not dissipate its rated power and
illuminescence....

Cheers!

--
Eric van Es               | Cape Town, South Africa
@spam@vanesKILLspamspamilink.nis.za | http://www.nis.za/~vanes
LOOKING FOR TEMPORARY / HOLIDAY ACCOMODATION?
http://www.nis.za/~vanes/accom.htm

1997\09\18@030444 by Pasi T Mustalahti

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On Wed, 17 Sep 1997, Martin R. Green wrote:

> As far as lightbulbs go, they are not really affected by flicker because
> the hot filaments have a very long persistence.
PTM: Try this first. Take a Oskilloskope and a LDR. Speak after that.
I Tried myself with pulps with various wattage, with series resistors,
with series diodes and TRIACS.

Fluorescent lights,
> however, do pulsate in time with the AC frequency.  This is why those
> strobe rings on  LP turntables don't work with incandescent light.  You
> need fluorescent or neon illumination to set the turntable speed with this
> method.

PTM: Try first, speak after that.

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1997\09\18@101537 by Martin R. Green

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Pasi, I'm not sure what your point is here.  Are you saying that I'm wrong?
You don't need to check the light output with an LDR and a scope.  All
that will tell you is what the light is doing, not what effect it has on
the human eye.  And I speak based on past experience with stroboscopic
effects of various light sources.

Also, I'm talking about normal lightbulbs hooked up to straight mains
power.  Why are you introducing all sorts of variables like resistors,
diodes and triacs?  Read the original thread.


Martin R. Green
spamBeGoneelimarspamBeGonespambigfoot.com

----------
From:   Pasi T Mustalahti[SMTP:TakeThisOuTptmustaEraseMEspamspam_OUTUTU.FI]
Sent:   Thursday, September 18, 1997 3:02 AM
To:     RemoveMEPICLISTspamTakeThisOuTmitvma.mit.edu
Subject:        Re: Multiplexing Seven Segment Displays [OT]

On Wed, 17 Sep 1997, Martin R. Green wrote:

> As far as lightbulbs go, they are not really affected by flicker because
> the hot filaments have a very long persistence.
PTM: Try this first. Take a Oskilloskope and a LDR. Speak after that.
I Tried myself with pulps with various wattage, with series resistors,
with series diodes and TRIACS.

Fluorescent lights,
> however, do pulsate in time with the AC frequency.  This is why those
> strobe rings on  LP turntables don't work with incandescent light.  You
> need fluorescent or neon illumination to set the turntable speed with
this
> method.

PTM: Try first, speak after that.

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PTM, pasi.mustalahtiEraseMEspam.....utu.fi, EraseMEptmustaspamutu.fi, http://www.utu.fi/~ptmusta
Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk                    OH1HEK
Lab.engineer (PC support) Computer Center                       OI7234
Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
--------------------------------------------------------------------------

1997\09\19@022506 by Pasi T Mustalahti

picon face
On Thu, 18 Sep 1997, Martin R. Green wrote:

PTM: Sorry, I was in a hurry and didn't select my words. (english is not
my native language:)
I mean that I made some years ago some experiments with various light
sources. I wanted to have as clean light as possible. I was disapointed
with bulps. There came very annoying 100 Hz ripple. (we have 240V 50Hz)
Then I made another try with a diode in series with a bulp and got 50 Hz
half vawes as I expected. Only that their 'duty cycle' was less than 50%
because it took time for the filament to warm up. This 50 Hz is twice the
frequency that is needed in movies to make flickerfree picture. Still it
made an awfull flicker.
I continued my expertiments with a capasitor. In parallel connection with
a bulp and a diode in series with them I got a little better results =
cleaner light. With a triac and thyristor -power (zero point) I got very
much flicker.

The cleanest light I got when I connected three bulps in three phase line.
Another good method was using higher frequency. That was however
impossible those days, because we needed rather high power.

These stroboscobes in the LP players have very often been just ordinary
bulbs with rather thin filament (low power, 220V). I have myself use
normal 220V/60W when I check the speed of small synchron motors.
I know that fluorescent tubes are forbidden when you work with electric
tools. It does make sense.

{Quote hidden}

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Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
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