POVs: How To Get A Clear Image With A Single Pass
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POVs: How To Get A Clear Image With A Single Pass

by SamuelAaronWard on Sat Apr 11, 2009 6:18 pm


Okay, my POV is working pretty well now, but it still is not working the way I would like it to work. Let me explain...

As I understand it, persistence of vision works because there is some small time delay (nano or miliseconds) from the moment that light strikes the eye's retina and the signal is passed through the optic nerve until it reaches the brain. And because it is so much slower than the speed of light, a person effectively sees multiple successive images as a single moving image (like cartoon animation). I obviously have a very rudimentary understanding of this phenomena; and I'm only looking for a solution to my problem, so all the sharp-shooters out there can impress someone else with their brilliant explanation paraphrased from wikipedia. :wink:

Here's the problem: I would like to be able to give a single wave of my POV and easily see the entire message. Instead, what I see is a very brief and incomplete piece of the message. It's only when I affix my POV to my ceiling fan (or the rotating contraption I made today) that I'm able to see it a little better. Then by taking dozens of digital photographs, I'm able to get a couple decent pictures. I suppose that the shutter speed of my digital camera is just slow enough that I can capture about a second's worth of exposure - thereby getting a complete, fixed image of my message. ...But I want to be able to see this with my naked eye - not only with a camera.

I know that things like the metranome-style POV clocks work by showing the image multiple times and inverting the message horizontally on the reverse stroke of the metranome thingy. And I'm wanting to be able to see it with only one pass, which might be a tall order. I'm not sure. The only factors, as I can see, are the frequency of the flashing message and the speed of my waving of the POV. If it takes me .5 seconds to complete a single wave of the POV, then what would I have to do to the frequency of the flashing? Speed it up? Slow it down? And exactly what would I have to change in LadyAda's original MiniPOV ASM code?

I'm not very good with Assembly programming, so any suggestions would be appreciated!

Aaron :)
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Re: POVs: How To Get A Clear Image With A Single Pass

by Mrmadsci on Thu Aug 23, 2012 2:49 am

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Re: POVs: How To Get A Clear Image With A Single Pass

by mtbf0 on Mon Aug 27, 2012 10:39 am

well, the good news is that the minipov is programmed in c.

the bad news is that these things are just kind of hard to see when you're swinging your arm around. you've got times when your arm's accelerating and decelerating and there's just bad timing, when you begin swinging the thing in the middle of the message. or you blink.

in the source code file minipov.c, find the following line

Code: Select all | TOGGLE FULL SIZE
  OCR1A = (uint16_t)10000;

if you find that the letters in the display look compressed, because you're swinging the gizmo around too fast, try increasing the value 10000. if the the display appears stretched out, try decreasing it.
"i want to lead a dissipate existence, play scratchy records and enjoy my decline" - iggy pop, i need more
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Re: POVs: How To Get A Clear Image With A Single Pass

by adafruit_support_bill on Mon Aug 27, 2012 11:27 am

The other factor that influences the POV effect is the level of ambient light. You will get a much stronger POV effect in a darker environment.

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Re: POVs: How To Get A Clear Image With A Single Pass

by john444 on Mon Aug 27, 2012 1:06 pm

Hi Samuel,

ISTM you need something to iniate a single cycle of the message.
You might use a tilt switch (id 173) as a trigger.
I suspect that you could learn to trigger the POV at various positions of your 'wave'.
Implementing this suggestion in software will be left to others.

Good luck, John

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