Saturday, January 23, 2010

Playing with Persistence

Since my croquis class was unexpectedly canceled today, I found myself with a couple of hours of spare time. I've been wanting to build a POV-gadget (Persistence of Vision) since I first saw the one by ladyada ( and with nothing else to do, I started going through my electronic supplies.

The design is really basic. Take one attiny84, 8 LEDs and 8 resistors (to limit the current through the LEDs). The idea is to flash the diodes at 400Hz to create an image (using the persistence of human vision). The image will appear if you quickly move the LEDs (or yourself) back and forth.

I created an image in GIMP and used the "save as .h-file" to get a C-style array. It needed some minor post processing, like transposing, but it was fairly straight forward.

The C-code to control the LED's turning on and off is inspired by the ladyada implementation. It uses a timer interrupt every 1/400 second to set the LEDs to show the next column of the image. I'm using the internal RC-resonator on the avr chip since precision timing is not important here, so there is no need for a crystal.

So how did it come out? Well, it's kind of hard to get an image of it... but by rapidly moving the camera I managed to get a decent picture.

I'm such a h4x00r :)

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