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How to Create a POV Virtual Pennant
My brother-in-law is a classic Chicago kind of guy, a sports fan born and bred. So for Christmas this year, I decided to make him something that would help him celebrate his favorite team.
I created a virtual pennant that uses POV (persistence of vision) to draw "GO CUBS" in the air as you wave it. The pennant consists of a blue baton with five LEDs in a row near the top. Wires lead out from the bottom of the baton to a black box with an on/off switch. Inside the box, there's an Arduino board running a program that causes the LEDs to blink in a particular sequence.
When the pennant is waved back and forth, the eye and brain conspire to "fill in the gaps" between the millisecond-long blinks, resulting in the illusion of letters hanging in the air.
I've started writing a detailed how-to to share with others who might want to build their own POV pennant. I'll be submitting it to MAKE and/or Instructables.com, and publishing it here as well.
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Comments
C. J. Newton
January 19, 2009 at 4:53 AMCan you make one big enough to be seen from a long way away?
Corey Ehmke
January 19, 2009 at 5:14 AMIt actually looks clearer the further away you are. But the answer is yes, the letters could be twice their current size-- probably up to about 4" tall.
Kenward
January 19, 2009 at 3:06 PMVery cool! At one point in the video it looks like CUBS is going backwards. Is that an artifact of the speed at which you are waving it?
Corey Ehmke
January 19, 2009 at 3:37 PMMost POV devices spin, so you never see this backward effect. In this case, since the pennant is moving back and forth, when you move it from left to right the words are correct, and they reverse when going in the other direction. The only workaround I could think of would require blacking out the LEDs altogether for a certain period of time, but that would require more precise timing of the waving to have any effect at all.
jhaneyzz
January 23, 2009 at 2:01 AMYou could add two momentary contact switches that are actuated by contact with the top (or bottom) of the "wand" contact with either switch would reverse the "polarity" of the logic and change the drawing direction.
jhaneyzz
January 23, 2009 at 2:03 AMI forgot to add that the above comment would assume that you house the wand in an enclosure (like your logic housing) and pivot the wand via a contact point in the unit.
Corey Ehmke
January 25, 2009 at 3:25 AMI like the idea of the user waving the pennant naturally. I think the problem could be solved by integrating an accelerometer that would detect the direction of the wave-- but that would raise the construction cost by about $16...
