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)

A light shines down onto a spinning disc, which has desgins printed on it in shades of gray.  The designs actually correspond to x and y coordinates for an image, which can be viewed using an oscilloscope.

Also posted at thing-a-day:
(The song is called Demozipan, featuring Bignose. It was found at under a Creative Commons license. Thanks!)

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2 Responses to Thing-a-day, Day 1: Light Record

  1. steve says:

    neat idea. i have a song on a paper album here, which plays very much like a vinyl record. i figure if you printed it out on paper, and setup your rotating table to read outwards as it spins, you could get the song to play.


  2. mahto says:

    Hey Steve, I like your record project! I would imagine that actually getting a physical player to follow the audio track might be difficult. Have you tried to make a physical player for them?

    Also, any ideas on what the bandwidth of the paper media/sensing head provides?

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