I have been intrigued by the idea of using UV LEDs to "write" on a phosphorescent surface ever since I saw this posted on the Make: blog. I already had a bunch of UV LEDs that I received when I thought I was ordering purple LEDs. And I previously built one of my POV boards with these UV LEDs. It worked great when swiping across the various glow-in-the-dark material samples I had been collected over the years. [Tokyu Hands in Shibuya, Tokyo, has a great selection.] But instead of me moving the LEDs, I wanted to move the vinyl. And I wanted to find an interesting way to do this.
A few months ago I purchased a roll of phosphorescent vinyl from H&H Sign Supply. One of the challenges is that the vinyl is not really that flexible. It is flexible enough to apply (it has an adhesive back), but you would not want to continuously bend it. This means a "conveyor belt" approach would probably wear out or be problematic in one way or another.
One day it dawned on me to use a ring. With a ring I could suspend it on the shaft of a motor. And a ring with a large diameter would give me a long surface. This length would give the glow time to fade before it comes around again.
So I took a 24" square of the vinyl and used a string and a pencil to trace two circles. I planned on sticking the vinyl on a piece of posterboard I had, but the posterboard was 22". So the outer diameter was 22" and the inner diameter was 14". The vinyl actually has a metal backing to reflect the glow, but this made it a little difficult to cut cleanly around the circle. Normally that would not matter too much, but you might notice in the video where the circle slows down. This is at the spot where there is a bump in the circle.
I had a motor from a cassette player I took apart long ago. Conveniently this motor had both a pulley on the shaft and two mounting screws attached to the motor. I drilled a hole in a 24"x12" board for the motor pulley and two more holes for the screws. (It may look like I planned to have a 22" circle on a 24" board, but that was just luck.) I attached the motor to the board so that pulley was coming through the hole and was now in front of the board.
On the front of the board I mounted the UV POV board I made. This was the board I made earlier for my hand-held UV POV tests. To mount it, I removed one of the little legs and used a spacer on the top of the board to give me the distance I needed. The goal was to get the LEDs close enough to the vinyl but press against it. Otherwise it would affect the rotation. Thankfully the board was light enough that only a single mounting screw was needed.
The board and the motor are powered separately. For the first attempt, I used two AA batteries to power the motor. This made the ring turn a little two fast. The meant that the glow was not fading enough before the ring made a full rotation. In the Flickr set there is a picture where you might be able to see this. (Also you notice that the images are closer together.) In the second attempt I used only a single AA battery. This made the motor turn rather slowly, which was what I wanted.
The board uses a PIC16F628 and a dozen LEDs. For the current tests, only 8 LEDs are used. The board is powered with 3 AAA batteries. In the picture below you can see a binder clip. This is keeping the battery holder from falling to the floor.
The designs are all created using the Animator LED Animation Application I wrote some time ago.
In the first test I thought the images were too close, and it was hard to figure out what was what. I used the editor to add space after each of the images. I also modified the program to run at about a third of the speed. Before I did this all of the glowing images were too skinny, since the ring was turning too slowly.
Overall I am pleased with the outcome. This was just my first prototype. Ideally I would like to find a way to build a more permanent version, especially one where I could display messages. Also it would be useful to control the motor with the microcontroller.
View all of the photos on Flicker TheVaporTrail
As covered on Hack A Day