Thing-a-day, Day 1: Light Record

So, I signed up to participate in thing-a-day (my posts there). The idea is that you complete one (smallish) project per day, and blog about it. Since I am pretty close to doing that anyway, I didn’t think it would be much of a stretch. However, they stipulate that you don’t spend more than an hour on the project, which is going to be tough… I already broke with that protocol with this first project.
Anyway, this is what I thought of tonight. I call it a light record. I am using some photocells (hey, I have a lot of them!) to read the intensity of light that shines through a sheet of paper, upon which I have encoded an image using shades of grey. By spinning this paper around and shining a light through it, the image can be viewed on an oscilloscope. The circuit consists of two resistor dividers, one for each channel, made up of a photocell and a fixed resistor. When there is a large amount of light on the photocell, its resistance drops dramatically and the output voltage rises; when there is little light on the photocell, its resistance goes down and the voltage goes down as well. That’s it! There is a diagram here that attempts to do a better job at explaining the idea. (view the whole photo set)

Also posted at thing-a-day: http://www.thing-a-day.com/2008/02/02/day-one-light-record/
(The song is called Demozipan, featuring Bignose. It was found at http://freemusic.freeculture.org/ under a Creative Commons license. Thanks!)