Author Topic: Any Response Delay's ?  (Read 1536 times)

Offline Nightowlz1966

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Any Response Delay's ?
« on: May 15, 2013, 11:37:46 AM »
Hey Everyone
I am asking this question ahead of time here.
I am thinking about using the Falcon to do pixels on my house.
I haven't played yet with the config or the falcon yet but my
Hypothetical Question is.
If I outline house in pixel and have strings of say 200-250 pixels (with power injection of corse)
and I do an ALL ON command for a single color on the strand is there going to be any
noticeable delay from the start to the end of the strand in response ?
Brian Flanders
Sharpsburg Ga. http://christmasonthecreek.com http://www.facebook.com/ChristmasOnTheCreek I Thought I Had More Extension Cords

Offline David Pitts

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Re: Any Response Delay's ?
« Reply #1 on: May 15, 2013, 12:03:46 PM »
I do not think you will see any delays.
PixelController, LLC
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Offline Zeph

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Re: Any Response Delay's ?
« Reply #2 on: May 20, 2013, 05:54:42 PM »
Mos 2811 based pixels use the high speed mode of 800kbps.  Each pixel takes 24 bits which comes out to 30 usec. 

For 250 pixels in sequence, there will be about 7.5msec (249 * 30 us) of delay between sending the first and last pixel data from the controller to the first pixel.  (there woujld also be a much smaller delay of about 75 usec propagation delay (249 * 300 nsec) before the last pixel's data is delivered to it).

The actual time that the new values are displayed will depend on the pixels latching the data after a timeout, which is probably somewhat inexact (probably an RC timer?), but that is just noise in the timing without a difference from beginning to end of string.

It will also depend on when the next PWM cycle starts; the chip is spec'd at a minimum of 400 cycles/sec, so there could be up to another 2.5 ms to wait before the pixel begins displaying the new RGB levels, but that will be randomly distributed among the pixels and doesn't depend on the length of the string.

Overall, this should mean about  7.5 ms delay in the average start time at the end of the string, compared to the beginning, with potentially a few ms of pixel to pixel time variability which doesn't depend on distance.  I don't think that's likely to be visible to the eye.

If running at 400 Kbps, the delay rises to 15ms, still probably hard to detect visually.  It would be interesting to put the 250th pixel rignt next to the first one and see if one can detect a difference even under optimal conditions, but I really doubt it would be visible if they were separated.

Offline David Pitts

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Re: Any Response Delay's ?
« Reply #3 on: May 20, 2013, 06:06:02 PM »
Thanks Zeph for your input. As always very detailed and precise. 

Offline JonB256

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Re: Any Response Delay's ?
« Reply #4 on: May 20, 2013, 08:29:06 PM »
The synch between video and audio (at 30 frames per second) is frequently off by 33 msec (one frame). Lip movement to voice is probably the easiest thing to detect when "off."  Personally experience when editing video is that you can be off by one frame and nobody notices. Two frames and most people will (66 msec).  Three frames and everyone becomes a critic (99 msec - this is 1/10 of a second).

Offline Nightowlz1966

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Re: Any Response Delay's ?
« Reply #5 on: May 20, 2013, 09:31:16 PM »
Thanks everyone for the responses on being able to see delays. I guess I am just going to have to play and see what I see  ::)

 

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