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How did you calculate "total persistence"?
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How did you calculate "total persistence"?

by sagebrush on Tue Apr 14, 2015 4:17 am

Bit of a random question. I'm building my own spokepov-type thing using the little 8x neopixel sticks, and I'm wondering how you got the figures of 7/12/15 mph for "total persistence" with 1/2/3 units? What did you define total persistence as and where did that figure come from? 15 miles an hour with a 700c rim is only about 3 revolutions per second, which doesn't seem like enough to have the entire wheel appear lit simultaneously. I'd have thought you needed at least 10-15hz to get persistence, like a video. (I have not seen a SpokePOV in person).

BTW, thanks for posting the SpokePOV code...looking through it helped me write a much more efficient program for my own system :)
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Re: How did you calculate "total persistence"?

by adafruit_support_rick on Tue Apr 14, 2015 11:47 am

I don't think anybody calculated it. I think it's just empirical observation.

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Re: How did you calculate "total persistence"?

by sagebrush on Sun Apr 19, 2015 2:21 am

Ah, ok, thanks. I thought about it over the last couple of days and realized it's probably got much more to do with the "clearing time" of your retina than how quickly you can perceive a change in the image. The dazzle/afterimages from a bright light definitely persist in my eyes for at least a third of a second, which is enough to hit the described performance.

Thanks! Onwards to 3D-print the housing for the neopixel sticks...
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Re: How did you calculate "total persistence"?

by adafruit_support_rick on Sun Apr 19, 2015 10:32 am

Neopixels aren't recommended for POV applications, since the PWM frequency is only 400Hz.
https://learn.adafruit.com/adafruit-neo ... view#faq-6

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